Number One Circuits

Decibels Meter Circuit Using LM324

2009-12-09T14:48:00.000-08:00

This decibels meter circuit responds for sound pressure levels from about 60-70 dB(Decibels). That sound is picked up by an 8 ohm speaker, amplified with a transistors stage and LM324 op-amp section.

For audio signal input source, a dynamic microphone can be used but a small speaker was more sensitive. The remaining three sections of the IC LM324 quad op-amp are used as volts comparators and drive three indicator LEDs or incandescents which are spaced about 3dB apart.

An additional transistor is needed for incandescent lights as shown with the lower lamp. I used 12 volt, 50mA lamps. Each light represents about a 3dB change in sound level so that when all 3 lights are on, the sound level is about 4 times greater than the level needed to light one lamp.

The sensitivity can be adjusted with the 500K pot so that one lamp comes on with a reference sound level. The other two lamps will then indicate about a 2X and 4X increase in volume. In operation, with no input, the DC voltage at pins 1,2 and 3 of the op-amp will be about 4 volts, and the voltage on the (+) inputs to the 3 comparators (pins 5,10,12) will be about a half volt less due to the 1N914 diode drop. The voltage on the (-) comparator inputs will be around 5.1 and 6.5 which is set by the 560 and 750 ohm resistors.

When an audio signal is present, the 10uF capacitor connected to the diode will charge toward the peak audio level at the op-amp output at pin 1. As the volume increases, the DC voltage on the capacitor and also (+) comparator inputs will increase and the lamp will turn on when the (+) input goes above the (-) input. As the volume decreases, the capacitor discharges through the parallel 100K resistor and the lamps go out. You can change the response time with a larger or smaller capacitor.

This decibels meter circuit requires a well filtered power source, it will respond to very small changes in supply voltage, so you probably will need a large filter capacitor connected directly to the 330 ohm resistor. I managed to get it to work with an unregulated wall transformer power source, but I had to use 4700uF. It worked well on a regulated supply with only 1000uF.

Source: Decibels Meter Circuit with LM324

Digital Sound Level Meter

2009-12-09T14:31:00.000-08:00

This circuit is a digital sound level meter with a LCD screen, capable of displaying 80 characters (4 rows with 20 characters on each). You can build this LCD display. It also provides more debugging information, such as the minimum and maximum analog-to-digital samples that were measured during each period.

Analog Amplifier Circuit
This is a simple model for the NPN bipolar junction transistor (BJT), biasing, how to calculate gain, and adding more gain at higher frequenies with a technique called "bypassing".

In the sound meter schematic, the 100K potentiometer is adjusted until the transistor's collector current is approximately 100 microamps (10-4 amps). This is measured with a voltmeter across RE until the voltage is approximately 0.33 volts. Please watch the video for a full explanation of the transistor model and how we build up to this circuit.

Source Code
Microcontroller are based around an Atmel ATmega168 series microcontroller (MCU). These are powerful, industrial grade MCUs, and we help you build a full system around them. This microcontroller has a CPU, permanent storage (flash memory), temporary storage (static RAM), and inputs and outputs.

You can download the source code here. Start with the standard NerdKits microcontroller project and Makefile (included with the kit) and plug in this source code.

Source: Piezoelectric Sound Meter

Regulated Power Supply 20A

2009-12-08T07:50:00.000-08:00

A heavy duty 13.8V regulated power supply is a fine thing to have in the shack, but unless you acquire one secondhand, is an expensive little beastie to buy. This means building one should be considered, not only for the cost savings, but also because you can brag about it on air to your mates. Of course, careful consideration must be given to the properties of the completed supply, and after talking to a few of my friends who have built their own and fallen into all the traps, here are the printable ones : RF proof, easy to make, commonly available parts used, but above all CHEAP.

The details published provide a transformer and rectifier structure capable of providing 8 amps DC continuously (and short current peaks up to 20 amps). This is sufficient to adequately power SSB transceivers with 100W PEP outputs, BUT WILL NOT power a transceiver providing a continuous carrier of greater than about 40 watts.e.g. AM, FM, continuous key down morse, single tone SSB testing etc. Demanding a continuous output of more than 8 amps will result in the transformer secondary overheating, with a possible fire risk. The reason we can get away with a supply with an 8 amp continuous rating is simply that speech is very "peaky" data, and so SSB has the odd high power peak but a very low average power level (usually about 20 -30% of peak value). It is on this basis that transformer and heatsink sizes are usually selected for domestic hi-fi equipment.

The winding resistances of the transformer have been very carefully chosen to avoid excessive current peaks which will cause failure of the 35 amp bridge rectifier. If you wish to use a transformer with higher current ratings to make a continuously rated 20 amp supply, you MUST use more heavily rated diodes with peak repetitive surge current ratings of around 800 amp.

The second part of the circuit (filter caps and regulator) will supply 20 amps continuously and can be used unchanged in a heavier duty supply. The transformer, rectifiers, and regulator circuit all generate large amounts of heat, and fan cooling MUST BE PROVIDED for safe and satisfactory operation.

Source: THE SSB20 POWER SUPPLY-20 AMPS

Variable Power Supply 12V

2009-12-08T07:16:00.000-08:00

Here's a 12V variable power supply circuit. Features: 1.3-12.2 V, 1 A, over-current protection. It's a simple but reliable device based one of the oldest integrated voltage regulators of them all - the LM723.

Power Supply Configuration
R2 sets the output voltage. The maximum current is determined by the value of R3: the over-current protection circuitry inside the LM723 senses the voltage across R3 and starts shutting the output stage off as soon as this voltage approaches 0.65 V. This way the current through R3 can never exceed 0.65/R3, even if the output is shorted.

C3 and C4, both ceramic, must be placed as close as possible to the integrated circuit, because the LM723 can be prone to unwanted oscillations. It is not an overkill to solder them directly (and very carefully) to the pins of the IC. All other connections should also be kept short.

The LM723 works with input DC voltages from 9.5 to 40 V and the IC itself can source some 150 mA if the output voltage is not more than 6-7 V below the input. When an external pass transistor is used (in the usual emitter-follower mode), the base-emitter junction of T1 represents a significant resistance and the integrated circuit's output stage is relatively lightly loaded. All the current drawn by the load passes through T1 and it dissipates an amount of power that is directly proportional to the current and the difference between the input and the output DC voltage.

The plastic box is only 160x140x60 mm, yet everything found its place in it somehow. Both meters are second-hand items, but properly shunted, with new face plates and freshly calibrated dials.

Power Supply Specification
Output (approximate values):

Vmin = (R4 + R5) / (R5*1.3)
Vmax = (7.15 / R5) * (R4 + R5)

Imax = 0.65/R3

Max. Power on R3: 0.42/R3

Min. Input DC Voltage (pin 12 to pin 7): Vmax + 5

Power Supply Parts List
B1 40V/2.5A
C1 2200uF (3300uF even better)
C2 4.7uF
C3 100nF
C4 1nF
C5 330nF
C6 100uF
D1 Green LED
D2 1N4003
F1 0.2A F
F2 2A M
IC1 LM723 (in a DIL14 plastic package)
R1 1k
R2 Pot. 5k
R3 0.56R/2W

R4 3.3k
R5 4.7k
S1 250V/1A
T1 2N3055 on a heatsink 5K/W
TR1 220V/17V/1.5

Source: Small Variable power Supply

High Voltage Power Supply for Geiger Tubes

2009-12-08T06:40:00.000-08:00

These power supply circuits are generating 500 volts but they may be modified to supply a couple of hundred to nearly 1000 volts by changing the zener diodes. These circuits generate high voltages and can cause dangerous shocks! Do not build these devices unless you are experienced and qualified to work on high voltage devices
.
The difference is subtle; the feedback signal increases the voltage on the base of the 2N4403 to stop the oscillator instead of stealing current from the capacitor on the emitter. The result is much lower power dissipation when there is little or no load on the high voltage. The new circuit draws less than 1/2 mA when operating at 9 volts without a load using a 1:1 600 ohm audio isolation transformer.

The 3 volt circuit may be modified in the same way but make sure to switch to a MPSA18 (or a similar very high gain transistor). The 120 volt zeners are also an improvement over trying to grade ordinary diodes; grading is just too much trouble! A 1N5273A is a typical type to try. Remember, this circuit can only supply a few microamperes so an ordinary 10 megohm voltmeter will load the output too much. (500 volts/10 megohms = 50 uA.)

Note
With some transformers and zeners, the circuit will work better if the 10 megohm resistor is moved up to be in series with the diodes (see next schematic). It is a good idea to add a resistor in series with the diodes anyway, perhaps 100 k, to prevent damage when probing around. When operating properly, the current should drop down to below 1/2 mA with no load. The series 10 megohm resistor will make gas discharge devices work well in place of the zeners, too (neon bulbs, for example). Also try a .1 uF capacitor from base to emitter of the MPSA18. This capacitor modification combined with the series 10 megohm allowed a single Lumex gas discharge tube to regulate the output voltage of the circuit at 600 volts while drawing only 300 uA, unloaded.

The transformer in the prototype is a small isolation transformer with opposite ends of the primary and secondary connected together to boost the output voltage. Other transformers will also work, including tiny audio interstage transformers, as long as the impedance is relatively high on both windings. If you don't get a high voltage, try reversing one of the winding connections. If the current doesn't cut back with no load, try the techniques mentioned in the note above. The circuit will work without the secondary connection simply by connecting the collector of the MPSA42 directly to the first .02 uF cap. and diode and leaving the secondary winding disconnected. Using the two winding voltage boost is recommended when attempting to run the circuit on a lower supply voltage.

Source: High Voltage Generator for Geiger Tubes

Infrared Thermometer Module-MLX90614

2009-12-07T21:07:00.000-08:00

The MLX90614 Infrared Thermometer Module is an intelligent non-contact temperature sensor with a 90° field of view and a serial interface for easy connection to host microcontrollers. The MLX90614 sensor is designed for non-contact temperature measurements of objects placed within the sensor’s cone of detection. The sensor is comprised of an integrated ASIC and infrared sensitive thermopile detector. The sensor communicates with an SX20AC/SS-G coprocessor over a digital SMBus, which Parallax has programmed to simplify an otherwise fairly complex communication protocol.

Features

Outputs continuous data flow with an active alarm running in background
16-bit digital temperature output data, ranging from -70°C to 380°C
Auto-baud detection (2400, 4800, 9600, 19.2K, 38.4K) for microcontroller-to-MLX90614 communications
SIP module format fits easily in breadboards or through-hold prototype areas
Multiple modules can be connected from a single I/O processor pin for serial data flow
Module can act as a stand alone sensor for alarming control
Sleep setting for low power consumption
Starts up active without pre-programming using preset writeable defaults
90° Field Of View (10° FOV version available)

Infrared Thermometer: BASIC Stamp PIN Connections

With a temperature range of -70°C to 380°C, auto-baud detection and a programmable alarm setting, this module becomes very useful in many applications such as surface temperature measurement, human/animal presence detection or HVAC. Up to 100 modules can be connected on the same bus making multi-zone temperature measurement easy.

Source: MLX90614 infrared thermometer module

Rotary Phase Converter Schematic

2009-12-07T19:46:00.000-08:00

With the discussion before on the static phase converter, there isn't much to explain about the rotary phase converter. The rotary converter is nothing more than a second motor in the circuit which is acting as a generator. With the static converter, the tool's motor performed this function, but at the cost of some loss of power. With the rotary converter, the idler motor is under no physical load, but it cleans up the signal a little. If you examine the drawing below compared to the first drawing, the only difference is that we added the idler motor.

The output of the rotary phase converter is closer to being a true 3-phase source than the static converter. This provides more power to the tool motor, and also brings it up to speed faster. The rotary converter is best served when you have a motor which is started and stopped frequently, and you need the full power of the motor. Furthermore, a single rotary converter can drive several different 3-phase tools.

Setting up the rotary phase converter is the same as the static converter described above. The only decision to be made is the size of the idler motor. The idler motor needs to be larger than the largest tool which will be operated.

Since the static converter will provide a motor with 80% of it's normal operating power, and the rotary phase converter uses a static phase converter as a starter, your idler motor should be 125% of your tool(s) motor size. That is, if your tool is a 5 horsepower motor, your idler should be between 6 and 7 horsepower. It is always better to err on the high side, so I would use a 7 horsepower idler motor. If the converter will operate more than one tool, make sure the current rating of the idler motor is 125% of the sum of the tool motors.

Source: Phase Converters (Rick Christopherson)

3 Phase Converter-Miller System

2009-12-07T19:34:00.000-08:00

This phase converter could prove useful for anyone who wanted to run three phase motors or build a balanced phase rotary converter for running three phase powered equipment off of a single phase source. It’s also known around my parts as a Miller system.

This is not the crappy low power, low efficiency, weak starting phase converters that you buy from the dealers. This is a well proven good high powered high efficiency design that can make most unmodified three phase motors run on single phase with both full starting torque and normal running power and efficiency.

I have built dozens of them and many are in daily usage applications and have given years of uninterrupted service working as both motors, phase converter power sources, and a few are now in dual use applications where they do double duty as a motor driving a mechanical load and as a balanced phase source rotary converter that runs additional loads.

The run circuit
The two motor run capacitors go from each supply line (L1 and L2) to the third phase line L3. That creates two basic LC tank circuits which use the rotors spinning motion to create a simple phase shifting autotransformer effect in the motor itself once it’s up to speed. This is what makes it possible for the motor to run up to its full working power rating. This is also how the three phase windings are able to work at the proper phase angle relationships to each other so as far as the physics are concerned the rotating magnetic field sees three sine wave power sources with a 120 degree phase angle separation between them.

If the voltage is higher than around 115% of the incoming line voltage the capacitor values need to be bigger. If it’s lower than 90% of the incoming line voltage they need to be smaller. And always keep them equal. This is keeping the LC tank circuits tuned to near the line frequency and is what keeps the current loads between each phase balanced using that phase angle shifting autotransformer effect.

Source: 3 Phase Converter Schematic (Miller System)

Build Your Own Gauss Meter

2009-12-07T11:10:00.000-08:00

Have you ever wanted to find out how strong a magnet really was, or how the strength of the magnetic field varied as you changed the distance from the magnet or the temperature of the magnet, or how well a shield placed in front of the magnet worked? Voltmeters are fairly inexpensive and easy to find, but where do you purchase a Gaussmeter (also known as a magnetometer). I built a hand-held Gaussmeter for measuring the polarity and strength of a magnetic field. It uses a linear Hall effect device and some op-amps and resistors and things from Radio Shack.

Here's a schematic of the Gauss meter circuit (using the 3503 Hall-Effect Device):

With no magnet near the Hall device, measure and note the output voltage reading. Call this V0. It should be about 2.50Vdc.

Now, with a magnet near the Hall device, you will see the output voltage change. If it is a South pole, the voltage will increase. If it is a North pole, the voltage will decrease. Call this voltage reading V1. We will say that the sensitivity of the Hall device is 2.50mV/G as found on their data-sheet. Call this k. Therefore, the Magnetic Flux Density you are measuring from that magnet can be calculated as:
B = 1000*(V0-V1)/k, in Gauss.
Please note that with a calibrated Hall device, you would be given actual data measurements for the V0 value and for the k value.

For example, suppose you measured 2.48Vdc for V0 and 1.32Vdc for V1.
Then B = 1000*(2.48-1.32)/2.50 = 464Gauss, North pole (because it is positive).

For another example, suppose you now measured 4.56Vdc for V1 with the same Hall device.
Then B = 1000*(2.48-4.56)/2.50 = -832Gauss, South pole (because it is negative).

See how easy that is? You can make your own plot using Excel so you don't have to calculate all the time. If you're taking measurements, just write down the output voltage and do the calculations later.
You can simply use it to tell you if you have a North if the output voltage decreased from V0, or a South pole if the voltage increases from V0.

Here are some photos of this simple, inexpensive Gauss meter.

Assembly was easy and exciting, and here is what I've found so far (NOTE: You may know all of this already):

Pickup covers do affect the magnetic field that the strings vibrate in. The most pronounced drop in gauss is over the slug polepieces. The adjustable polepieces have significantly more power than covered ones.
Strat magnets can have a significant difference in gauss in the same pickup.
All magnets are not the same, and PAF pickups have a significant difference in gauss from pickup to pickup.
The Dimarzio PAFs have almost exactly the same magnetic characteristics of a Gibson PAF.

Download Gaussmeter Circuit Documentation

About

2009-11-25T02:10:00.001-08:00

About The Author

I'm just a Blogger to spend my spare times

Contact

2009-11-25T02:09:00.001-08:00

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If you have any questions regarding the content in this weblog, about the products that are mentioned, or just any questions at all don’t hesitate to contact me at the following email address: 1stcircuits@telkom.net.

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2009-11-11T07:57:00.000-08:00

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