electronic-4y

Trip circuit to touch a base NE555

2014-11-30T07:32:00.002-08:00

This circuit is used to trigger a relay with a 12 V the touch of the hand. He uses the ability of
conduction of the skin. Once again the master of the house is the indestructible NE555 timer; in this circuit is mounted conventionally monostable configuration.

Attach it to the handle of the door and that it protects the entrance to your studio, your bedroom or even your secret drawer. When he touches the handle, the key lock ... the intruder receives the ringing of the alarm siren in the ears (controlled by relay) and prefers to slip: 90 dB of a mermaid that makes very sore eardrums and then think it will round up the world! This type of connection is also perfect to surprise
the guest at a party in his honor when he touches the handle, a light string lights and, why not, a welcome message, good party ... is reproduced! But you can also use it to start with a simple touch of the hand, a pre recorded message. Or to protect against the fridge kind of nocturnal predators (no, not necessarily children ...) as soon as the nocturnal visitor touches the handle opening, a small alarm (more discreet than for real thieves) sounds, and
puts in trouble, facing his vice bulimic! But stop there the enumeration of these applications suggestions because we are certain that you will find many others.

The wiring diagram:

To operate the circuit, Figure 1 shows the circuit diagram, a 9V battery is sufficient (but a 12 V - car battery or 230 V - both will do). The NE555 was mounted in monostable configuration: its output pin 3 remains in the condition it is in the power until the voltage on pin 2 (normally it is that of food) goes down below 1/3 of the supply voltage.

The timer begins for a given time T by the formula:
T = 1.1 x R2 x C2
The voltage on pin 2 goes down when we touch with hand the wire connected to the trimmer R1: this action
determines a connection to the earth through our body. The capacitor C1 initially charged by the supply voltage, discharges through R1, in series with the resistance of the body, towards the earth and the voltage on pin 2 drops to 0 V.

The consequence is that a voltage pulse is formed on pin 3, for a time T that impulse drives the base of the transistor TR1 becomes conductive and supplies the winding of the relay. In parallel with this coil we set up an LED DL1, without forgetting its R5 current limiting resistance, too, when the relay glue, the LED lights.

The DS1 LED is connected in parallel with the relay coil, but it is as celleci protection against surges. Indeed, in a solenoid, whenever a voltage change occurs, a sign inverse electromotive force takes place and without the diode which cancels, wherein the transistor is damaged it will discharge.

The practical realization:

First realize (Method of blue film) from the scale drawing 1: 1 in Figure 2b the single sided printed circuit or get it. When you're looking at, first press (with a small hammer and by relying on a metal plate drilled a hole) the stud welding going trigger wire to the touch. Insert the media also 2 x 4 pins of the integrated circuit, but insert it at the end. Then insert all components, you then solder on. Start Up
by inserting the five resistors, capacitors and two polyesters two electrolytic capacitors carefully observing the polarity of these: the - sign is screen printed multiple times
along the corresponding housing of the "leg" negative. The - C1 and C3
go to the ground strip which forms an L on the left side of the circuit. Continue inserting the transistor
TR1, benchmark-keyed (pin its metal housing) oriented in the right direction: towards mass L. track Solder the LEDs in the AK holes (in the relay), taking care that the polarity:
the anode A into hole A and cathode K in the K hole; knowing that the longest leg of an LED is the anode. If you think you should deport this LED for your personal application, extend its legs with plastic-coated copper wire: black for the cathode K - and red for anode A +. The flat surface of the transparent housing of the LED corresponds to the cathode K, as shown in Figure 2a, but it is difficult to see. Insert the two trimmers and over and finally the two terminals. Flip the board and solder all the pins and tails all components carefully. Also solder the pin. Cut the remaining lengths. Make sure the welds (shiny, without short circuit between tracks or pads or cold solder joints) before inserting the NE555 in its holder, landmark-keyed U oriented C4.
Component side, now screw the two son going to 12V (or
in decision-9V) in the bottom terminal, red + left and the black - right. Into the terminal screw top three son, connected to the relay outputs, they are used to control the load (the siren for the applications we considered at the beginning of the article). For all this use 2a and
3 but also the wiring diagram in Figure 1 and the list of associated components. So you will not go wrong. These tips are for beginners, since the purpose of this triptych is primarily didactic.

List of components:

R1 ...... 1M trimmer
R2 ...... 220 k trimmer
R3 10k ......
R4 ...... 1k
R5 ...... 1k
C1 ...... 10 uF electrolytic
C2 ...... 4.7 nF polyester
C3 ...... 100 uF electrolytic
...... C4 100 nF polyester
DS1 ... 1N4007
DL1 LED ....
TR1 .... NPN 2N2222A
IC1 NE555 .....
RL1 .... 12V relay 1 contact
Other:
1 3-pin terminal block
1 2-pin terminal block
Note: resistors are quarter-W.

The setting of trimmers:

Turn their axes far left (counterclockwise) and far right (clockwise) and then adjust them mid Feed the race circuit with a 9V battery or 12V (battery or power adapter small constant) .dropoff window As long as you do not touch the TEST wire (yellow Figure 2a), nothing happens; from
you touch it, the relay trips and LED lights. After some time, precisely adjustable with the trimmer R2 TIME, the relay turns off. R1 SENSITIVITY trimmer serves him to adjust the trigger touch sensitivity of the circuit. If you find that from time to time the relay trips without reason, act on the axis of R1 to stabilize the relay.

An Automatic Sealed Lead-Acid Battery Charger

2012-03-15T16:09:00.003-07:00

This nifty charger is just what you need to keep your SLA batteries up to snuff

The K2 uses a Power-Sonic PS-1229A 12-V, 2.9-Ah sealed lead-acid (SLA) battery. SLAs are commonly called gel-cells because of their gelled electrolyte. As with all things, to obtain maximum service life from an SLA battery, it needs to be treated with a certain degree of care.
SLA batteries must be recharged on a regular basis; they should not be undercharged or overcharged. If an SLA battery is left unused, it will gradually self-discharge.
Although my SLA battery experiences related here are linked to my K2 transceiver, you can think of the K2 simply as a load for the battery. The comments pertaining to the SLA batteries and chargers apply across the board and the charger described here can be used with any similar battery.

Using a Three-Mode Charger
My first attempt at keeping my K2’s SLA battery healthy was to purchase an automatic three-mode charger. I soon discovered that most three-mode chargers work by sensing current and were never intended to charge a battery under load.
Three-mode chargers begin the battery charging process by applying a voltage to the battery through a 500-mA current limiter. This stage is known as bulk-mode charging. As the battery charges, its voltage begins to climb. When the battery voltage reaches 14.6 V, the charger maintains the voltage at that level and monitors the battery charging current. This is known as the absorption mode, sometimes called the overcharge mode. By this time, the battery has achieved 85% to 95% of its full charge. As the battery continues to charge with the voltage held constant at 14.6 V the charging current begins to drop. When the charging current falls to 30mA, the three-mode charger switches to float mode and lowers the applied voltage to 13.8V. At 13.8 V, the battery becomes self-limiting, drawing only enough current to offset its normal self-discharge rate. This works great until you attach a light load to the battery, such as turning on the K2 receiver. The K2 receiver normally draws about 220mA. When the charger detects a load current above 30 mA, it’s fooled into thinking that the battery needs charging, so it reverts to the absorption mode, applying 14.6V to the battery. If left in this condition, the battery is overcharged, shortening its service life.

UC3906-IC Chargers
Chargers using the UC3906 SLA charge-controller IC work just like the three-mode charger described earlier except that their return from float mode to absorption mode is based on voltage rather than current. Typically, once the charger is in float mode it won’t return to absorption mode until the battery voltage drops to 10% of the float-mode voltage (or about 12.4V). Although this is an improvement over the three –mode charger, it still has the potential for overcharging a battery to which a light load is attached.
First, let’s look at the situation where a UC3906-controlled charger is in absorption mode and you turn on the K2 receiver, applying a load. The battery is fully charged, but because the load is drawing 220mA, the charging current never drops to 30mA and the charger remains in absorption mode, thinking that it is the battery that is asking for the current. As with the three-mode charger, the battery is subject to being overcharged.
If we remove the load by turning off the K2, the current demand drops below 30mA and the charger switches to float mode (13.8 V). When the K2 is turned on again, because the charger is able to supply the 220mA for the receiver, the battery voltage doesn’t drop, so the charger stays in float mode and all is well.
However, if the transmitter is keyed (increasing the current demand), the charger can’t supply the required current, so it’s taken from the battery and the battery voltage begins to drop. If we unkey the transmitter be fore the battery voltage reaches 12.4 V, the charger stays in float mode. Now it takes much longer for the charger to supply the battery with the power used during transmit than it would have if the charger had switched to absorption mode.

Fig: 1

C1, C2 - 2200 µF, 35 V electrolytic
C3, C6, C7, C8 - 0.1 µF, 50V metallized
C4, C5 22 µF, 25 V tantalum
D1 - 400 V, 4 A bridge rectifier
D2 - 1N5245, Zener diode, 15 V, 500 mW
D3 - Bicolor LED, red/green
D4 - 1N5820 Schottky diode
F l - 250 mA slow-blow fuse
J1 - 2-pin header, PC mount
J2 - 2-pin connector, PC mount
J3 - 3-pin connector, PC mount
Q1 - 2N4401 NPN transistor
R1 - 1 kΩ 1 W, 5%
R2 - 240 Ω
R3 - 2.4 Ω 1 W, 5%
R4 - 2.2 kΩ
R5 - 12 kΩ
R6 - 150 Ω

R7 - 1 MΩ
R8 - 3.6 kΩ
R9, R10 10 kΩ
Rll - 100 Ω 1/4 W, 1 %
R12-16.2 k" 1/4 W, 1%
R13 - 20 kΩ, multiturn pot
R14, R15 - 680 Ω
T1 -15 V/666 mA
UI - LM137 - T voltage regulator, TO-220 case
U2 - LM555 - timer
U3 - LM78L12 voltage regulator, TO-92 case
U4 - LM358 - dual opamp
U5 - LM336, 2.5 V voltage reference, TO-92 case
Misc: PC-boeard(3); TO-220 heat sink; five 1/4 inch #4-40 stand-offs; two fuseholder clips, PC mount; two-pin shunt; two-pin connector housing; three pin connector housing four housing pins; enclosure

SLA batteries must be recharged on a regular basis.

Let’s key the transmitter again, but this time keep it keyed until the battery voltage drops below 12.4 V. At this point, the charger switches to the absorption mode.
When we unkey the transmitter, we’re back to the situation where the charger is locked in absorption mode until we turn off the receiver.

Why Worry?
So, why this concern about over-charging an SLA battery? At 13.8 V, the battery self-limits, drawing only enough current to offset its self-discharge rate (typically about 0.001 times the battery capacity, or 2.9 mA for a 2.9 Ah battery).
An SLA battery can be left in this float charge condition indefinitely without overcharging it. At 14.6 V, the battery takes more current than it needs to offset the self-discharge. Under this condition, oxygen and hydrogen are generated faster than they can be recombined, so pressure inside the battery increases. Plastic-cased SLA batteries such as the PS-1229A have a one-way vent that opens at a couple of pounds per square inch pressure (PSI) and release the gases into the atmosphere.
This results in drying the gelled electrolyte and shortening the battery’s service life.
Both undercharging and overcharging need to be avoided if we want to get maximum service life from the battery.
Continuing to apply 14.6 V to a 12-V SLA battery represents a relatively minor amount of overcharge and results in a gradual deterioration of the battery.
Applying a potential of 16V or excessive bulk-charging current to a small SLAbattery from an uncontrolled solar panel can result in serious overcharging. Under these conditions, the overcharging can cause the battery to overheat, which causes it to draw more current and result in thermal runaway, a condition that can warp electrodes and render a battery useless in a few hours. To prevent thermal runaway, the maximum current and the maximum voltage need to be limited to the battery manufacturer’s specifications.

Design Decision
To avoid the potential of overcharging a battery with an automatic charger locked up by the load, I decided to design my own charger, one that senses battery voltage rather than current in order to select the proper charging rate. A 500-mA current limiter sets the maximum bulk rate charge to protect the battery and the charger’s internal power supply. Like the three-mode chargers, when a battery with a low terminal voltage is first connected to the charger, a constant current of 500mA flows to the battery. As the battery charges, its voltage begins to climb. When the battery voltage reaches 14.5 V, the charger switches off. With no charge current flowing to the battery, its voltage now begins to drop. When the current has been off for four seconds, the charger reads the battery voltage.
If the potential is 13.8V or less, the charger switches back on. If the voltage is still above 13.8 V, the charger waits until it drops to 13.8 V before turning on. The result is a series of 500-mA current pulses varying in width and duty cycle to provide an average current just high enough to maintain the battery in a fully charged condition. Because the repetition rate is very low (maximum of one current pulse every four seconds) no RFI is generated that could be picked up by the K2 receiver. Because the K2’s critical circuits are all well regulated, slowly cycling the battery voltage between 13.8 V and 14.5 V has no ill effects on the transmitted or received signals.

Thermal runaway can warp electrodes and render a battery useless in a few hours.

As the battery continues to charge, the pulses get narrower and the time between pulses increases (a lower duty cycle). Now when the K2 receiver is turned on and begins drawing 220mA from the battery, the battery voltage drops more quickly so the pulses widen (the duty cycle increases) to supply a higher average current to the battery and make up for that taken by the receiver. When the K2 transmitter is keyed, it draws about 2 to 3 A from the battery. Because the charger is current limited to 500mA, it is not able to keep up with the transmitter demands. The battery voltage drops and the charger supplies a constant 500mA. The battery voltage continues to drop as it supplies the required transmit current. When the transmitter is unkeyed, the battery voltage again begins to rise as the charger replenishes the energy used during transmit. After a short time, (depending on how long the transmitter was keyed) the battery voltage reaches 14.5 V and the pulsing begins again. The charger is now fully automatic, maintaining the battery in a charged condition and adjusting to varying load conditions.
The great thing about this charging system is that during transmit the majority of the required 2 to 3 A is taken from the battery. When you switch back to receive, the charger is able to supply the 220mA needed to run the receiver and deliver up to 280mA to the battery to replenish what was used during transmit.
This means that the power source need only supply the average energy used over time, rather than being required to supply the peak energy needed by the transmitter. (You don’t need to carry a heavy 3-A regulated power supply with your K2.) As long as you don’t transmit more than about 9% of the time, this system should be able to power a K2 indefinitely.
Have you ever noticed that sometimes when your H-T has a low battery and you drop it into its charger you hear hum on the received signals? This charger’s power supply is well filtered to ensure that there is no ripple or ac hum to get into the K2 under low battery voltage conditions.

Circuit Description
The charger schematic is shown in Figure1. I’ve dubbed the charger the PCR12-500A, short for Pulsed-Charge Regulator for 12-V SLA batteries with maximum bulk charge rates of 500mA.
U1, an LM317 three - terminal voltage regulator, is used as a current limiter, voltage regulator and charge-control switch. A 15-V Zener diode (D2) sets U1 to deliver a no-load output of 16.2 V. R3 sets U1 to limit the charging current to 500mA. When Q1 is turned on by the LM555 timer (U2), the ADJ pin of U1 is pulled to ground, lowering its output voltage to 1.2 V. D4 effectively disconnects the battery by preventing battery current from flowing back into U1. A Schottky diode is used at D4 because of its low voltage drop (0.4 V).
An LM358 (U4A) operates as a voltage comparator. U5, an LM336, provides a 2.5-V reference to the positive input (pin 3) of U4. R11, R12 and R13 function as a voltage divider to supply a portion of the battery voltage to pin 2 of U4A. R13 is adjusted so that when the battery terminal voltage reaches 14.5 V, the negative input of U4A rises slightly above the 2.5-V reference and its output switches from +12 V to 0 V. When this happens, the 1-MΩ resistor (R7) causes the reference voltage to drop a little and provide some hysteresis. The battery voltage must now drop to approximately 13.8 V before U4A turns back on.
U4B is a voltage follower. It pulls the trigger input (pin 2) of U2 to 0V , causing its output to go to 12 V. U4B’s output remains at 12 V until C5 has charged through R6 (approximately four seconds) and the trigger has been released by U4A sensing the battery dropping to 13.8 V or less. While the output of U2 is at 12 V, emitter/base current for Q1 flows via R5 and Q1’s collector pulls U1’s ADJ pin to ground, turning off the charging current.
The output of U2 also provides either +12 V or 0 V to the bicolor LED, D3. R14 and R15 form a voltage divider to provide a reference voltage to D3 such that D3 glows red when U2’s output is +12 V and green when U2’s output is at 0 V. When ac power is applied but U1 is switched off and not supplying current to the battery, D3 glows red. When U1 is on and supplying current to the battery, D3 is green. As the battery reaches full charge, D3 blinks green at about a four-second rate. As the battery charge increases, the on time of the green LED decreases and the off time increases. A fully charged battery may show green pulses as short as a half-second and the time between pulses may be 60 seconds or more.
T1, D1, C1 and C2 form a standard full-wave-bridge power supply providing an unregulated 20 V dc at 500mA. U3, an LM78L12 three - terminal regulator, provides a regulated 12-V source for the control circuits.
Note that the mounting tab on U1 is not at ground potential. U1 should be mounted to a heat sink with suitable electrically insulated but thermally conductive mounting hardware to avoid short circuits.
Suitable mounting hardware is included with the PC board .

Other Bulk-Charge Rates
The maximum bulk-charge rate is set by the value of R3 in the series regulator circuit. The formula used to determine the value of this resistor is R ohms = 1200/ImA.
T1 must be capable of supplying the bulk charge current and U1 must be rated to handle this current. The LM317T used here is rated for a maximum current of 1.5 A provided it has a heat sink sufficiently large enough to dissipate the generated heat. If you increase the bulk-charge rate, you’ll definitely need to increase the size of the on-board heat sink. Mounting U1 directly to the housing (be sure to use an insulator) may be a good option.

Transformer Substitution
I selected T1 because of its small size and PC-board mounting. You can substitute any transformer rated at 15 or 16 V ac (RMS) at 500mA or more. You may find common frame transformers to be more readily available. You can mount such a transformer to an enclosure wall and route the transformer leads to the appropriate PC-board holes.

Construction
There is nothing critical about building this charger. You can assemble it on a prototyping board, but a PC board and heat sink are available.
The specially ordered heat sink supplied with the PC board is 1/4-inch higher than the one identified in the parts list and results in slightly cooler operation of U1. The remaining parts are available from Digi-Key.
Be sure to space R1 and R3 away from the board by 1/4 inch or so to provide proper cooling. R13 can be a single-turn or a multi turn pot. You’ll probably find a multi turn pot makes it easier to set the cutoff voltage to exactly 14.5 V.

R13 Adjustment
To check for proper operation and to set the trip point to 14.5 V dc, we need a test-voltage source variable from 12 to 15 V dc. A convenient means of obtaining this test voltage is to connect two 9-V transistor-radio batteries in series to supply 18 V as shown in Figure 2. Connect a 1-kΩ resistor (R2) in series with a 1-kΩ potentiometer (R1) and connect this series load across the series batteries with the fixed-value resistor to the negative lead. The voltage at the pot arm should now be adjustable from 9 to 18 V. During the following procedure, be sure to adjust the voltage with the test supply connected to the charger at J2 because the charger loads the test-voltage supply and causes the voltage to drop a little when it’s connected.
Remove the jumper at J1 and apply ac line voltage to the unit at J3. Turn R13 fully counterclockwise. D3 should glow green. Connect the test voltage to J2 and adjust R1 of Figure 2 for an output of 14.5 V.
Slowly adjust R13 clockwise until D3 glows red. To test the circuit, wait at least four seconds, then gradually reduce the test voltage until D3 turns green.
At that point, the test voltage should be approximately 13.8 V. Slowly increase the test voltage again until D3 turns red. The test voltage should now read 14.5V.
If it is not exactly 14.5V, make a minor adjustment to R13 and try again. The aim of this adjustment is to have D3 glow red just as the test voltage reaches 14.5 V.
To test the timer functioning, remove the test voltage from J2 and set it for about 15V. Momentarily apply the test voltage to J2. D3 should turn red for approximately four seconds, then turn green. The regulator is now calibrated and ready for operation. Remove the test voltage and ac power and install the jumperat J1.

Figure 2—Test voltage source for the

battery charger. (The component

designation for the push-button switch

differs from QST style.)

A Suitable Enclosure
I used an 8×3×2.75-inch LMB Perf-137 box (Digi-Key L171-ND) to house the charger. An alternative enclosure is the Bud CU482A Convertabox, which measures 8×4×2 inches (available from Mouser). If you use the Convertabox, be sure to add some ventilation holes directly above the board -mounted heat sink. The LMB Perf box comes with a ventilated cover. If you are inclined to do some metal work, you could build your own enclosure using aluminum angle stock and sheet and probably reduce the size to perhaps 8×3×2inches.
If you use a PC-board-mounted power transformer, watch out for potential shorts between the transformer pins (especially the 120-V ac-line pins) and the case. If you use a metal enclosure, connect the safety ground (green) wire of the ac-line cord directly to the case.

Operation
It is very important that this charger be connected directly to the SLA battery with no diodes, resistors or other electronics in between the two. The charger works by reading the battery voltage, so any voltage drop across an external series component results in an incorrect reading and improper charging. For example, the ElecraftK2 has internal diodes in the power-input circuit, so it’s necessary to add a charging jack to the transceiver that provides a direct connection to the battery. Now I can leave my K2 connected to the charger at all times and be assured that its internal battery is fully charged and ready to go at a moment’s notice.

Multi-Purpose Car Scrolling Display

2012-03-04T08:48:00.006-08:00

In this article, we guide you through the construction of the Car Scrolling Display.
We also show you how to install the software driver that’s used to communicate with the display via a USB port on a Windows PC.

All the parts for the Car scrolling Display are installed on two pc boards – a main board coded 786 (134 × 86mm) and a display board coded 787 (124 × 75mm). These two boards are stacked together with a red Perspex window and are secured using nylon spacers, washers and screws.
Note that there is no wiring between the two boards. The display board simply plugs into the main board via connector CON6.
Note also that the display board is smaller than the main board. That’s been done so that when the two boards are stacked together, the screw terminal blocks on the main board are exposed for easy access.

Main board assembly
Fig.6 shows the assembly details for the main board. Begin by checking the board for cracks in the tracks or any shorts between adjacent tracks.
This is easier to do before installing the parts and can save you trouble later.
Once you are convinced that the pC board is OK, start the assembly by soldering in the 10 wire links. You must do this first, as two of these links (lK5 and lK6) are underneath the 40-pin IC socket.

These links should be installed sing tinned copper wire. You can straighten this link wire by first clamping one end in a vice and then pulling the other end with pliers to stretch the wire slightly. After that, it’s simply matter of cutting the links to length and using pliers to bend their leads own at right angles so that they fit the PC board.
There are 24 resistors on the main C board, and they can be soldered in next. You must make sure that the correct value is used at each location. The color code table shows how to decipher the values, but it is also prudent to check each one with a multimeter before it is soldered in place. Note that the 10Ω resistor must be rated at 1W.
Once the resistors are in, the diodes can be installed. There are eight diodes in total, of four different types.
Begin by installing 16V Zener diode ZD1. Refer to the component overlay for its location and orientation! Remember that the cathode of a diode is normally indicated by a stripe.
The signal diode (D7, a 1N4148) is used for ICSP (in-circuit serial programming) and is installed near CON5 (the ICSP header). You only really need it if you intend to program the microcontroller (IC1) in circuit; otherwise it can be left out.
Diodes D5 and D6 are next on the list. Note that these were shown as 1 N 5 8 1 9 Schottky types on the circuit diagram (Fig.3) last month, but in practice, 1N4004 diodes will do, and that’s what are now specified in the parts list. Be sure to install them with the correct orientation.
By contrast, diode D4 must be a 1N5819 Schottky type (as originally specified). This can now be installed, followed by the five remaining diodes, which are all 1N4004s.
The four transistors can now all go in. These are all BC337 NPN types and each must be correctly oriented, as shown in Fig.6.
Now for the capacitors. The ceramic and the 100nF monolithic capacitors are not polarized and can go in either way around. However, the electrolytic capacitors are polarized, so be sure to install them as indicated on the overlay.
Note particularly that all the electrolytic capacitors must have their leads bent by 90° so that their bodies lie horizontally on the PC board – see photo.
Do not mount them vertically; if you do, they will interfere with the bottom of the display board when the boards are stacked together.

Once you’ve installed the capacitors, you are ready to install the connectors and the IC socket. Install the 40-pin IC socket first, making sure that it is oriented correctly with its notched end as indicated. Note that the IC is not installed in the socket just yet. That step comes later, after some preliminary checks of the supply rail.
Install the right-angled 6-pin ICSP header (CON5) only if you intend to program the microcontroller. Note that you will need to cut away the plastic locating guide on this connector if you intend to use the PicKit2 programmer from Microchip. In addition, CON5 should be mounted about 2mm above the PC board in order to ft the PicKit2 programmer.
The rest of the connectors are screw terminal blocks CON1 to CON4. These consist of 2-terminal and 3-terminal blocks, which are combined by sliding their dovetailed ends together.
As shown, CON1 and CON4 are each made by sliding two 2-terminal connectors together, while CON3 consists of two 3-terminal connectors. CON2 is a single 3-terminal connector.

Making up CON6
CON6, a 27-way connector is made by frst cutting a 40-pin IC socket into two 20-pin sockets. You can use a small fne-toothed hacksaw to do this job.
As shown on Fig.6, CON6 is split into three parts. The first is a 14-pin connector; the second is a 5-pin connector and the last is a 7-pin connector (note: pin 15 is not used). You make these by first cutting one 20-pin connector into 14-pin and 5-pin connectors. The 7-pin connector is then cut from the remaining 20-pin connector.
Regulator REG1 can go in next. As shown, this device is mounted horizontally with its leads bent down by 90°, to go through their matching PC board holes. In addition, the regulator must be fitted with a small U-shaped finned heatsink, and this is sandwiched between the regulator’s tab and the PC board.

Secure this assembly to the PC board using an M3 × 10mm screw, lockwasher and nut before soldering the regulator’s leads. If you solder the leads first, the soldered joints may crack as the mounting screw is tightened down.
Note that we specified an LM-2940CT-5 low drop-out regulator in the schematic (Fig.3), you can also use a common (and much cheaper) 7805 regulator in its place, if you wish.
The only drawback here is that using the 7805 means that you will have to power the circuit from a 12V supply. By contrast, the LM2940CT-5 will work with supply voltages down to as low as 9V.
The LM2940CT-5 also contains in-built reverse polarity protection, but we don’t use it in this circuit. That’s because reverse polarity protection is provided by diode D1.
Construction of the main PC board can now be completed by installing the 20MHz crystal. It’s non- polarized, so it can go in either way around.

Display board assembly
Fig.7 shows the parts layout on the display board. Begin the assembly by installing the 21 wire links (LK1 to LK21). Some of these links are quite long and run close together, so it’s important that they are straight before they are installed (stretch the link wire to straighten it).
The resistors can go in next. Note that the 3.3Ω resistor must be rated at 0.5W, while the others are all rated at 0.25W.

Now solder in the two 16-pin IC sockets. These must be oriented with their notched ends as shown on Fig.7.
Note that although these sockets are optional, we do recommend them.
They make it much easier to replace the ICs, if necessary.
The next step is to install six 7-pins socket strips to accept the dot-matrix LED arrays. These are made by cutting three 14-pin IC sockets in half and then cleaning up the edges using a small file. That done, the sockets strips can be soldered in place.
These sockets are used simply to space the LED arrays off the board, so that they later sit close to the red
Perspex front panel. They also make it easier to replace a module in the unlikely event that it fails.
You can now install the two ICs in their sockets, making sure they are correctly oriented. Don’t get these two ICs mixed up – IC2 is the 74HC595 shift register, while IC3 is the ULN2003 Darlington array.
The three LED modules can also be installed in their sockets, each with pin 1 at bottom left. Pin 1 of each module is indicated by a digit on the side.
Once this is done, you can solder in the 15 BC327 transistors. Be sure to orient them as shown and push them down onto the board as far as they will comfortably go before soldering their leads.
Next, solder the two capacitors in place. The 100nF monolithic type is not polarized, but the 470μF electrolytic is, so take care when installing it.
The three pin connector strips that make up CON7 can now be installed.
These are made from a 32-way strip that’s cut into three pieces of 14, 7 and 5 pins. As shown in the photo, these are installed from the component side of the PC board.
Now install the USB type B socket. It sits vertically on the PC board and only fits one way around. Its two tabs can be bent fat against the underside of the board to secure it in position before soldering. Solder its four pins and both tabs to the PC board.
The last thing to do is to solder in the LDR. This should be installed about 10mm above the PC board, so that it later sits just below the front panel.
That completes the assembly of the two PC boards. The next step is to make the front panel.

Fig.8: follow this drilling and cutting diagram to make the front panel. It’s made from 3mm-thick red Perspex measuring 124mm × 75mm.

Preparing the front panel
The front panel is made from a single piece of red Perspex measuring 124 × 75mm (ie, the same dimensions as the display board). Fig.8 shows the cutting and drilling details. There are four 3mm-diameter holes for securing it to the display board, plus a larger (13mm) hole for pushbutton switch S1.
In addition, you need to make a square cut-out to provide access to the USB socket.
Once you’ve cut and drilled the panel, fit the pushbutton switch in place and wire it back to the display board using two 60mm lengths of hook-up wire. The front panel is then fitted with four M3 × 12mm tapped nylon spacers, plus four nylon washers which are secured using M3 × 25mm nylon screws – see Fig.9.
The display board can now be fitted in position over the nylon screws.
Another four nylon washers are then fitted, after which another four M3 × 12mm nylon spacers are wound on.

Preliminary tests
Before attaching the main board, it’s a good idea to carry out a power supply check to confirm that the +5V supply rail is correct. Note that this should be done with microcontroller IC1 OUT of its socket.
First, connect a 12V battery to the power input terminals of CON1 (pin 4 is the +12V input, pins 2 and 3 are ground). Apply power and check the voltage at pin 1 of CON3. If it’s close to +5V, then everything is in order. Note that this voltage can normallyrange from 4.9V to 5.1V. A voltage above 6V or lower than 4.5V indicates that there is a problem and you should disconnect power immediately.
Assuming that the +5V rail measures. OK, you can now disconnect power and install IC1 in its socket. Note that this IC must be programmed with the firmware hex file. If you are building this project from a kit, it will be supplied preprogrammed.

Final assembly
Having checked that the +5V rail is. OK, it’s time to complete the assembly.
This simply involves plugging the display board into the main board and then securing the assembly using four M3 × 6mm nylon screws.

Switch on
Once the assembly has been completed, apply power (ie, via CON1).
You should now see a message scroll past on the LED display modules.
Among other things, this default welcome message should show the firmware version.
If you see this, then everything is working correctly and you can proceed to the next section, which explains how to install the software driver on your PC. If not, you should refer to the troubleshooting panel.

Driver installation
The USB device interface for the Car Scrolling Display uses the generic Microchip driver for Windows. Before communicating with the display using the PC host program, you will need to install this driver. This section explains how to install the driver in
Windows XP, although other versions of Windows will be similar.
The first step is to download the Microchip installer (MCHPFSUSB_Setup_v1.3.exe) from the EPE website and run it. Note that you should use version 1.3, as older or newer versions may not be compatible. The installer program will typically put the driver in the C:\MCHPFUSB\Pc\MCHPUSBDriver\Release folder.
Next, connect the Car Scrolling Display to your computer using a USB cable. Windows will recognize the device as a ‘Display’ and then the ‘Found New Hardware’ Window will appear as shown in Fig.10. Select the ‘No, not this time’ option and click ‘Next’. You will now be presented with a new dialog window. Select ‘Install from a list or specific location’ and click ‘Next’ again to bring up the dialog shown in Fig.11. Select ‘Search for the best driver in these locations’ and enable the ‘Include this location in the search’ box.
Now click the ‘Browse’ button. In the ‘Locate File’ window that appears, navigate to where the MCHPUSB files were installed (normally C:\MCHPFUSB\Pc\MCHPUSB Driver\Release) and select ‘mchpusb.inf’.
Click ‘Next’ and Windows will then install the driver.
If the driver is installed correctly, the ‘Microchip Custom USB Device’ entry should now be visible if you go into Device Manager (Control Panel >System ¬> Hardware tab ¬> Device Manager Button) – see Fig.12 (provided the device is connected).

Using the host software
Once the driver has been installed successfully, you control the Car Scrolling Display using the PC host program cardisplay.exe. This program allows you to change all settings and to do data logging. It is also used for calibration.
Once you’ve connected the Car Scrolling Display’s inputs to the sensors you are interested in monitoring, you can then use a laptop in your car to perform the calibration (you only have to do this once) or change any other system settings (such as the display brightness).

You can also use a laptop in your car to do real time data logging of the signals. Of course, you will need someone else to do the driving while you do this!
To install the PC host program, you first have to download the compressed file ‘cardisplay.zip’ from the EPE web-site (www.epemag.com). You’ll find it in the downloads library section.
Extract the files in the zipped archive to a folder on your hard drive.
There should be at least two files:
1) cardisplay.exe – this is the executable command line program
2) cardisplay.map – this file is used internally by the host program. It must be in the same folder as cardisplay.
exe for the program to recognize it.
Note that the map file is produced by the C compiler of the firmware. It contains memory mapping information for the firmware produced by the linker. When and if the firmware is updated, the map file will also change and this new file must be copied to the folder containing cardisplay.exe in order for it to work correctly.
So, installing the PC host program is easy – just copy the cardisplay.exe and cardisplay.map files to your chosen folder. Once that’s done, you simply go to a command prompt to run the program using your chosen command line option.

45-second Voice Recorder Module

2012-02-27T12:17:00.004-08:00

Here’s a voice recorder design that can be set up easily to record two, four or eight different messages for random-access playback or a single message for ‘tape mode’ playback.
Also, it provides clean and glitch-free line-level audio output suitable for
Feeding an amplifier or PA system. It can be powered from any source of 9-14V DC.

SOLID-STATE voice recorders are popular projects. They can be used in all sorts of applications where messages or sounds need to be recorded and played back reliably under either manual or micro control.
Such projects often have annoying limitations – for example, they can only be used to record and play back one long message or a number of short messages in sequential ‘tape recorder’ fashion. Such design limitations are often unnecessary, because the recorder chips used are typically capable of recording and playing back up to eight messages in ‘random access’ mode.
Another common limitation is that the playback sound quality can be fairly noisy, and each message played might be accompanied by an irritating ‘click’ at the start and finish.
Reader feedback revealed another limitation: older modules have been designed to operate from a 6V battery, whereas many people wanted to use a nominal 12V DC source.
Design concept
It was with these limitations in mind that we decided to develop the sound recorder module described here.
It’s based on the HK828 chip, with the rest of the circuit designed to al-low flexibility in terms of message storage and to provide much cleaner and click-free playback audio. Finally, the circuit can run from any source of
DC between 9V and 14V.
The HK828 chip has the ability to store single or multiple messages with a total length of between 40 and 60 seconds, depending on the sampling rate and the voice quality you want.
In this recorder module, the chip is teamed up with a low-cost electret microphone insert to allow easy message recording, plus an LM358 dual op amp IC, which allows the recorded messages to be played back as a line-evel audio signal, available for feeding an external amplifier and speaker.

Getting the message
We’ve given this module a set of ‘jumper links’, so that it can be easily configured to record and play back messages in any of four modes: either two, four or eight messages in random access mode, or one or more messages in sequential access ‘tape mode’. Another link allows the HK828 chip’s message start ‘beeps’ to be enabled or disabled, as you wish.
All message selection, record and play functions are controlled externally, via connections to a row of screw terminals along the side of the module.
All functions are enabled by switches or logic signals.
This makes it easy to record or play back messages using a set of pushbuttons and a switch or under the control of a PC, microcontroller or security system if you prefer.

How it works
The HK828 chip forms the functional heart of the recorder module, therefore you need to have a rough idea of what goes on inside this chip in order to understand how the recorder works. Fig.1 shows the chip’s basic architecture.
First, the chip includes a high-gain microphone preamp so that it can be driven directly by a low-cost electret microphone insert. An automatic gain control (AGC) circuit follows the preamp, to ensure that good quality recordings can be made without any need for manual gain adjustment, despite input signal level variations.
The output of the AGC circuit is not connected directly to the chip’s recording circuitry, but is brought out to the ‘Aout’ pin instead. This is linked to the ‘Ain’ pin by the user, to record messages from the microphone.
This arrangement allows the chip to be used to record from line-level signals in other applications.
Since the main part of the HK828 records by a process of sampling the audio signals fed into it via the Ain pin, it needs to pass these signals through a low-pass filter befor the sampling. This is done to prevent distortion caused by sampling aliases, hence the 'anti- aliasing' filter between the ‘Ain’ input and the sample and hold circuit block.
Now, although the audio is sampled inside the HK828, this is done using an analogue sample-and-hold system, rather than the more common digital sampling system. It stores the samples in an array of 262,144 (256K) Flash EEPROM analogue storage cells, each of which can store any of 256 different voltage levels. This gives the equivalent of 8-bit digital recording.

Fig.1: the block diagram of the HK828 voice recorder chip.

While the recording process relies on audio sampling, the audio is not stored digitally, but uses an analogue sample-andhold system.

The analogue samples are stored in the cells of a 256K Flash EEPROM. Each analogue storage cell can store any of 256 different voltage levels, making it equivalent to an 8-bit digital recording.

Sampling rate
The capacity of the storage array means that the HK828 can store a total of 256K samples. How long a recorded message this gives depends on the sampling rate that’s used.
For example, if the sample rate is 8000 samples per second, 256K samples will correspond to a total message length of just over 32 seconds (262,144/8000). However, if you sample at 4200 samples/second, the 256K samples will give a total message length of just over 62 seconds (262,144/4200).
The recording band width or 'fidelity' is directly proportional to the Sampling rate.
So, if you sample at 4200 samples/second, the recording bandwidth will be just over 2kHz, whereas sampling at 8000 samples/second gives a bandwidth of just on 4kHz.
Choosing the sampling rate is therefore a compromise: the lower the sampling, rate the longer the recording time, but the lower the audio and width.
Conversely, the higher the sampling rate the higher the bandwidth, but the shorter the recording time.
The HK828 chip has an internal sampling rate clock oscillator, as well as an input for an optional external clock.
Either clock signal can be fed to the sample and hold circuit via the multiplexer (MUX), to control the sampling.
The frequency of the internal oscillator is set by varying the value of an external resistor connected between the ‘OscR’ pin and ground. This circuit uses a 47k�� resistor, which sets the sampling rate to about 5800 samples/second. This gives a message recording time of about 45 seconds and a bandwidth of about 2.9 kHz, for reasonable voice-quality recording.
As shown in Fig.1, the recording and playback of samples in the storage array is controlled by analogue write and read circuits, along with the message control and message decoding circuits.
When a message is being played back, the signals pass through another low-pass filter to remove sampling noise, and are then fed to the inbuilt output amplifier.
The rest of the circuitry inside the HK828 chip is used for overall device control, mode switching and so on.

Circuit details
The complete circuit details for the Multi-Message Voice Recorder is shown in Fig.2.
As shown, signals from the electret microphone insert are coupled into the MICin input of the HK828 (pin 17) via a 100nF coupling capacitor. Another 100nF capacitor is used to tie the preamp’s second MICref input (pin 18) to ground, to provide maximum gain.
The 4.7μF capacitor and 220kΩ resistor connected between pin 19 and ground are used to optimise the chip’s AGC attack and decay characteristics for speech. The amplified audio from the mic preamp and AGC circuit appears at pin 21 (Aout), which is coupled directly to pin 20 (Ain) via another 100nF capacitor.
As mentioned earlier, the internal sampling oscillator frequency is set to 5.8 kHz by the 47 kΩ resistor connected to ground from pin 7 (OscR).
Setting the HK828 into record or playback modes is achieved by an external switch or logic signal connected to the RecEnable terminal, which connects to the chip’s RE pin (27).
The terminal is pulled to ground for record mode or allowed to rise to logic high level (+5V) for playback mode. Note that when the terminal is pulled down to ground for record mode, this also allows transistor Q1 to draw base current and turn on – allowing current to flow through LED2, the record mode indicator.
Link LK1 is used to enable or disable the HK828’s message-starting ‘beep’, by changing the logic level at pin 11 (‘Beep Enable’). Similarly, links LK2 and LK3 are used to set the desired message recording and playback mode, as shown in the small table on the circuit diagram.

Message recording
To record a message in one of the random access modes, all that needs to be done is to pull down the RecEnable line to force the chip into recording mode, and then pull down one of the message-select lines (eg, M1Enable or M2Enable) using an external pushbutton or a logic signal from a PC or microcontroller.
The message select line must be held down for the duration of the message recording; recording ends when the line is allowed to rise high again.
To play the recorded message, the RecEnable line is allowed to rise high again, and the message select line for the message you want to replay pulled down again for about 400ms.
The playback audio emerges in push-pull (ie, anti-phase) fashion from pin 14 and pin 15 of the HK828, the SP+ and SP– pins, and is connected to a 100�� load resistor. The signals are fed via 100nF capacitors to a balanced-to-unbalanced matching stage using IC2b, one half of an LM358 dual op amp.
This effectively adds the two signals together, and cancels out the ‘common mode pedestal’ signal that appears with them on both outputs.
As a result, the output audio signal at pin 7 of op amp IC2b is clean and ‘glitch free’. This is then passed through op amp IC2a, connected as a voltage follower/buffer and then fed to the line-level audio output socket.
All of this part of the circuit operates from +5V DC from REG1, an LM78L05 regulator. We are able to use a low power regulator because the total current drain is quite low: about 4mA in standby mode, rising to about 45mA when a message is actually being played or recorded.
There’s one remaining point which should be mentioned about the circuit.
You’ll note that the HK828 chip is provided with a ChipEnable pin (pin23), which in this circuit is pulled down to earth via a 47kΩ resistor – so the chip is enabled by default.
However, the ChipEnable line is also brought out to a terminal, to allow you to apply a logic high (+5V) to this line if you want to disable the chip for any reason. You might want to do this if you have a microcontroller or PC controlling a number of the modules, in which case it will need to be able to select between them using their ChipEnable lines.

Construction
All of the components used in the components used in the Voice Recorder module fit on a compact PC board, coded 797, measuring 119mm × 57mm. This board is available from the EPE PCB Service.
The board can be mounted inside a standard UB3-size plastic box.
Since all of the screw terminals and connectors are along one side of the board, they will all be accessible via a slot or series of holes along that side of the box. Only three holes will be needed in the box lid: two 5mm holes for LED1 and LED2, and a larger hole to allow sound to reach the electret mic insert.

The location and orientation of all components on the board can be seen in the overlay diagram of Fig.3, and also in the matching photo of the module.
Start board assembly by fitting the four screw terminal blocks, then the DC input and audio output sockets. Follow these with the two IC sockets, the three 2-pin headers for links LK1 to LK3 and the short wire link, which fits just near the end of the 28-pin IC socket. After this, you can fit the resistors and smaller non-polarized capacitors.
Next come the 4.7μF tantalum and the electrolytic capacitors, which are also polarized, so make sure you fit them with the orientation shown in the diagram.
Now you’ll be ready to fit the semiconductor parts. These are also polarized, so make sure you follow the diagram carefully as a guide to their orientation. Fit diode D1 first, then transistor Q1 and the two LEDs, followed by regulator REG1.
Now fit the electret mic insert. This has only two wire leads, but it is polarized, so do check the back of the insert to make sure which lead connects to the metal body of the insert. This is the negative lead, which must be connected to the ‘earthy’ outer pad under the board. The other lead is the positive lead.
Finally, plug the LM358 op amp IC2 into its 8-pin socket and the larger HK828 chip IC1 into its 28-pin socket.
Make sure they’re both orientated as shown in Fig.3. Your Multi-Message Voice Recorder should now be complete and ready to go.

Trying it out
To check that your recorder is working correctly, first decide which message mode you want to use it in, and then place jumper shunts on link headers LK1, LK2 and LK3 to set the module for that mode of operation.
(Use the Table in Fig.2 as a guide.)
Connect a small toggle switch and one pushbutton switch (for each message you want to select) to the appropriate screw terminals of the module, as shown in Fig.4. For now, switch the toggle switch off, which corresponds to message playback mode.
The audio output of the module can now be connected to the line input of any suitable audio amplifier. Then you can connect its DC power input to a source of 9V to 14V DC.
At this stage, neither of the LEDs should light, but you may hear a small turn-on ‘plop’ from the speaker connected to the external amplifier. If you wish you can use a digital multimeter to confirm that the supply voltage at pin 8 of IC2 is very close to +5V, relative to the module's earth terminal.
Now switch the external toggle switch on, pulling the RecEnable line down to earth potential. This should switch the module into Record mode, so LED2 should begin glowing.(If it doesn't begin glowing, you either have the DC power polarity reversed, or LED2 fitted to the board the wrong way around.)

Record/replay
Next, press one of the message select pushbuttons – say MSG1 in Fig.4. While
holding it down, begin talking into the electret mic to record your test message.
As you speak, you’ll notice that the green Strobe LED (LED1) is flashing.
Keep talking until you reach the end of your message or until LED1 stops flashing (which indicates that recording has stopped automatically, because you have reached the end of that segment of the HK828's memory). Then release the pushbutton.
To replay the recorded message, turn the toggle switch off to swing the module into Play mode and brifly press the message pushbutton again, but this time only briefly because in Play mode, the message buttons only trigger the replay operation.
Your recorded message should then be replayed through the external amplifier and speaker. If it does your Multi-Message Voice Recorder is working correctly and should now be ready for use.
Changing message length
As mentioned earlier, the total message length stored in the HK828 chip’s memory is determined by the sampling rate, which is set by the resistor connected from pin 7 of the chip (OscR) to ground.
The 47kΩ value shown for this resistor in the circuit and overlay diagram gives a sampling rate of 5800 samples/second, resulting in a total message length of 45 seconds and an audio bandwidth of about 2.9kHz.
We picked this as a reasonable compromise between message length and recording quality, but you can experiment with the value of this resistor to try longer/shorter recording times and narrower/wider audio bandwidth.
For example, if you change the resistor value to 82kΩ this will lower the sampling rate to about 4200 samples/second and gives a total recording time of just on 60 seconds. However, the audio bandwidth will also drop to around 2 kHz, so the played-back message(s) will sound rather 'muffled' a bit like talking through a wet sock!
On the other hand, if you lower the resistor value to 24KΩ, this will increase the sampling rate to about 8000 samples/second and drop the recording time to just on 32 seconds.
However, the recording quality will increase to about 4 kHz.
So, experiment by all means, and settle on the resistor value you decide gives the best combination of total message length and acceptable audio quality for your application.

Changing message mode
As noted earlier, header links LK2 and LK3 on the board can change the module’s message access mode.
For example, with a jumper shunt fitted to LK2 but removed from LK3, the module will be able to record and play two messages (each using half the HK828’s memory space).
You’ll only need two external pushbuttons to select one of these messages:
MSG1 and MSG2, along with the Record/Play toggle switch.
If you want to record and play four messages, remove the jumper shunt from LK2 and place one on LK3 instead. You’ll now need four external pushbuttons as well as the Record/Play toggle switch: MSG1, MSG2, MSG3 and MSG4. Note that in this case, each message will be able to use one quarter of the HK828’s memory.

Leave the jumper shunts off both LK2 and LK3 if you want to record and play any of eight short messages (each using one eighth of the HK828’s memory).
You’ll now need all eight external pushbuttons MSG1 to MSG8, along with the Record/Play toggle switch.
The last option is to fit jumper shunts to both LK2 and LK3, which sets the module for ‘tape mode’ operation.
In this mode, you normally only need one external pushbutton (MSG1), because the HK828 records and plays back either one message or a sequence of messages, using all of its memory space.
That’s it then – an easy-to-build solid-state Multi-Message Voice Recorder module that can be used for all kinds of applications, especially those involving sending pre-recorded messages over an amplifier or PA system under the control of a PC or microcontroller.