SCHEMATRONICS

RF Sensing Alarm

noreply@blogger.com (Go2Media) — Fri, 31 Oct 2008 05:40:00 +0000

RF sensing alarm is a device that would alert when it detects a continuous RF transmission that lasts more than 5 minutes. The device would have to be broadband (HF/VHF/UHF), be sensitive enough to detect a 5W transmission from inside the shack using a telescopic antenna, and produce a sound loud enough to alert me anywhere in the house.

The RF sensing alarm would also have to be self-contained, which means without any hookups to my radios. After a bit of reading and thinking, I came up with a solution that meets all the initial objectives. Here's circuit in detail.

The circuit shown above may look scary for some of you, but it is not. It can be broken down into four stages. Let's look at them one at a time. The first stage acts as a RF sensor circuit. It is made of U1C, one of the four operational amplifiers of a LM324 chip, and its associated input circuitry. U1C is used as a voltage comparator. Note that the two U1C inputs (plus and minus) have similar DC circuits connected to them. The plus input has R7, R8 and D3, and the minus input has R6, R10 and D5. In these two circuits, D3 and D4 are partly biased (about 200 mV of forward voltage) in order to better exploit the variation of voltage versus current that the diode produces. This translates into increased RF sensitivity.

More circuit description in detail

Simple Oxygen Sensor Simulator Circuit

noreply@blogger.com (Go2Media) — Sun, 13 Jul 2008 23:08:00 +0000

This electronic circuit is an oxygen sensor simulator built on a prototype board. Note the cigarette lighter plug used for power source. The adjustment knob is at the left, and the switch is on the right. The red indicator LED is in the middle. Only use red, because the voltage drop of the LED is part of the circuit!

The schematic diagram for the simulator. Closing the switch engages the simulator. Turning the knob clockwise simulates a lean condition, turns the LED off, and the car should start running rich to compensate. The big "V" is a digital voltmeter(not shown in the pictures). Using a smaller value for C1, perhaps 4.7 uF, will make the circuit oscillate faster and might be more like a real oxygen sensor(a new sensor switches more often than an old one).

The adapter cable. Note the connector recycled from an old oxygen sensor. Hard to see under the black tape: 100K resistor.

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ESR Meter

noreply@blogger.com (Go2Media) — Thu, 10 Jul 2008 16:27:00 +0000

The ESR Meter is basically an AC Ohmmeter with special scales and protective circuitry. It provides a continuous reading of series resistance in electrolytic capacitors. It operates at 100 kHz to keep the capacitive reactance factor near zero. The remaining series resistance is due to the electrolyte between the capacitor plates and indicates the state of dryness. Capacitor termination problems also show up plainly due to the continuous ohmic reading.

The ESR meter uses 8 operational ainplifiers. An op-amp is an idealized basic amplifier with two inputs. The non-inverting input (+) has an in-phase relationship with the op-amp output, and the inverting input (-) an out-of-phase relationship. Op-amps are usually used with negative feedback and reach a stable operating condition when their two inputs are equal in voltage.

Op-amps IA & 1B form a regenerative 100 kHz oscillatnr circuit. Capacitor C1 is the basic tiining capacitor and RI is selected to set frequency. Diodes D2 & D3 clip the bottom and top of the output waveform so that the output level and frequency are resistant to battery voltage changes.

The oscillator output of op-amp 1B drives 10-ohm source resistor R8F. The test-capacitor, thru the test leads, couples this 100 kllz signal to 10-ohm load resistor R9F. The amount of voltage developed here is indicative of the capacitors ESR value. (The 10-ohm resistors determine the basic iieter scaling.)

Capacitor C3 blocks any DC voltage present on the test-capacitor. Diodes D4 & D5 protect the ESR Meter from any initial charging current to C3. Resistor R7 discharges C3 after test.

A DC operating bias of 0.55 V is established by diode D1 for the oscillator stage and for all subsequent stages, which are DCcoupled and operated class A. DC bias from D1 and ESR signal from R9F are combined at the input of op-amp 1D. Both voltages are amplified by 1D, 1C, & 2A. Each of these three stages has an amplification factor of about 2.8 due to the ratio of output-voltage to feedback~voltage at the (-) input, which is determined -by feedback resistors R13F & R14F, etc.

Op-amp 2D is configured as a peak-to-peak detector. when the in-corning AC signal goes more positive than the normal bias level of about 0.77 Volt, the output of 2D also goes positive. But it must go positive enough to overcome the voltage drop across diode D6 before a fully equalizing positive voltage can be fed back to the -(-) input thru R20 to stabilize the op-amp.

-Capacitor C4 is charged to the peak value of the AC signal and accurately represents the peak of the incoming AC signal. The voltage drop across the diode becomes almost inconsequential due to the feedback process, and the circuit works down to a few mV.

A similar action occurs during the negative peak, using D7 & C5.

Resistor R21 provides a constant minimum amount of negative feed--back around op-amp 2D. The negative feedback increases the op-amp bandwidth which, most importantly, keeps the amplifier input-to-output phase-shift low enough for proper circuit operation.

The two outputs from the peak-to-peak detector are connected to two high-input-impedance unity-gain DC amplifiers, which drive the 1 mA meter movement differentially.

Source

A Tiny and Accurate pH-meter

noreply@blogger.com (Go2Media) — Sun, 06 Jul 2008 01:08:00 +0000

This electronic circuit is a tiny pH-meter. It is very tiny: 11cm2 including the PSU circuit! The schematic is shown below. It is basically a simple gain/offset circuit with a high impedance input (several giga-Ohm) and frankly the explanation could stop here: anyone with an background in electronics can understand this. But I started to write a webpage about this, so let's try to do it right and describe the schematic.

Juste because it's damn small does not mean that you have to settle down for second best when it comes to performance. The repeatability is around 0.01 pH and the accuracy, while depending on how well you will calibrate it, is around 0.02 pH. The main characteristics are:

very small footprint (11cm2)
very lightweight
pluggable module for easy replacement
requires only an external transformer and a display unit to work
slope/offset settings
repeatability 0.01 pH
accuracy 0.02 pH
low power
low-cost single-sided PCB
total unit price (including case and display unit): less than 100 euros.

The circuit input is pin 15 of K1. The probe signal enters IC1 via an RC circuit designed to allow only relatively slow signal variations (and avoid getting parasite HF signals). IC1 is a CMOS op-amp and thus has a very high impedance. The gain of IC1 is adjusted with the potentiometer R14. C2 is there for the amplifier stability. The R5/R11 circuit is the adjustment of the amplifier offset which is necessary for a high-precision application like this (see calibration below).
Once the signal has been amplified it enters an offset circuit built around IC2. IC2 is a more classic TL081 op-amp commonly found in audio devices, among others. The offset is defined by two potentiometers R12 and R13. The first one is on the PCB and the second one on the front panel. This improvement on the original design (single pot) allows the range swept by R13 to be symmetric, albeit smaller than without R12. It can be skipped if you wish (those small SMD trimmers can be damn expensive...). The circuit is designed to provide an average offset of 2V.
After the offset circuit the signal passes through a voltage divider before reaching the display unit. The divider roughly changes the signal range to something that is acceptable for the display. The real setting will be done on the display itself which contains a multiturn trimmer to precisely adjust its input gain.
The voltages for the signal evolve in the circuit as follows:

Before IC1: -0.414/+0.414V (this might depend on the electrode used and its age, hence the gain/offset control)
After IC1: -2/+2V
After IC2: 0-4V
After the voltage divider: 0-140mV (roughly)
After the on-display trimmer: 0-140mV
On the display: 0.00 - 14.00 pH (the display measures mV but the decimal point is placed accordingly to show a 0-14pH range)

As you can see the electrode voltage is symmetric and must undergo a linear transformation to fit the 0-14 pH range. This is all very classic stuff... Note that even if the supply rails are at +/-5V the circuit can cope with a 0-4V signal because the output swing is almost equal to the rails (no 0.7V drop, more around 0.3V IIRC).
A little remark concerning the integrated power supply circuit: it is a very small circuit that supplies a maximum of 50mA. Be careful of you want to add a power LED or something like that as it might be too much for the circuit. Check the total power used by the circuit before adding extras.
PCB
The PCB is very small and you are advised to build it with through-hole mounting components if you're not familiar with SMDs. That means start the PCB design from scratch. I personally think that it looks much cooler with a small footprint... No other special remarks concerning the PCB, except that the PCBs that were manufactured were slightly different (see the photos below). This is actually also true for the schematic. No functional difference, but I changed from Protel to Eagle for designing the circuit so I had to reenter the schematic and PCB manually. Hence some differences in layout but this is not a big deal.

Component list
This is the list of components used in this circuit. I only mention the display and probe at this time as the other components are generic. Maybe more info will follow in the future.

A little link to the display unit used in this project. I chose this one because it has a nice 'pH' unit that can be activated on the display.

Another link to the probe used with this circuit (IIRC). Most probes should work but I only tested the circuit with this one.
Construction

Random remarks: start with the smallest components, go slow, don't forget to set all the solder bridges correctly on the display unit (what you want is a 0-200mV range, an appropriately set dot and 'pH' shown as the unit). Check your cables,... before powering up.

The cabling diagram of K1 is:
* 1: AC 1
* 2: GND
* 3: +5v OUT (to display)
* 4: SIGNAL OUT (to display)
* 5: R13 / 2
* 6: R14 / 1
* 7: -5V OUT
* 8: R14 / 3
* 9: AC 2
* 10: GND (from transformer)
* 11: GND (to display)
* 12: GND (to BNC input)
* 13: R13 / 1
* 14: R14 / 2
* 15: INPUT

Source: ©Damien Douxchamps

I2C Temperature Sensor

noreply@blogger.com (Go2Media) — Tue, 01 Jul 2008 07:12:00 +0000

The electronic circuit is Temperature Sensor with I2C program. It is a circuit that plugs into the link port of a TI-85, TI-83, or TI-92 calculator and displays the temperature on the screen. Currently, there is only software for the TI-85, but I plan to write some for the TI-92 also. The sensor circuit draws power from the link port, so there is no need for any external batteries. The overall size of the unit will depend on the size you make it. Mine is about .75" by .5".

Parts

Two small switching diodes. I think that just about any kind will work.
I used 1N914 ones.
One small electrolytic capacitor. I tried 2.2uF, 10uF, and 100uF, and all of them worked.
An LM75CIM-5 integrated circuit (IC) made by National Semiconductor. For a more detailed description, you can read the data sheets on it onNational's WEB page at www.national.com and also check theirdistributors. It is a surface mount chip, so it is pretty hard to workwith.
A 2.5mm stereo plug and cord. You can buy one, but I just cut a calculator link in half.
A kit that allows you to etch your own boards. You can buy these at Radio Shack for about $15 and they can be used more than once. You canalso use another method, but I found this to be the cheapest for workingwith surface mount devices.
Construction Materials. Just general things like a soldering iron,solder, etc.

Directions

Come up with some way of using the surface mount IC. I etched my own PCB for it.
Solder all the parts for the circuit on the board or however you chose to make the circuit. Be sure to follow the schematic for this step. And make sure the red and white wires are connected correctly accordingto the schematic. The only part you don't have to follow is how youconnect the A0-A2 pins. You can find out what pins these are in the data sheets available on National's WEB page www.national.com read the next couple sections of these plans. If you connect them differently, you will have to change the chip ID which is explained below.

Software
The software I wrote to control the I2C Temperature Sensor is very simple to understand. Simply run the ZShell program and it will display the temperature on the screen in both Celcius and Farenheit. If an error message appears on the screen, this section will help you.

The program continuously updates the temperature about twice every second. To exit the program, simply press [EXIT]. There is also a feature that can be activated by pressing [F5]. This will allow you to change the chip ID that is set by the A0 to A2 pins on the IC. If this is set wrong, it will display an error on the screen. After pressing [F5], you can change the ID number by pressing [UP] and [DOWN]. Then, simply press [ENTER] and it will bring you back into the program. This also allows you to have up to 8 chips in the same circuit if you change around the circuit a little bit and give each one a separate chip ID set by the A0 to A2 pins. If changing the chip ID does not get rid of the error, make sure the plug is plugged into the calculator all of the way. If the error is still there, check over your construction of the circuit. If you have an error and change something external, either plugging in the cord or fixing something on the circuit, be sure to restart the program or alter the chip ID to restart the program.

Source Copyright Ed Plese, Jr.

Fluid Level Detector With LM903

noreply@blogger.com (Go2Media) — Fri, 27 Jun 2008 18:36:00 +0000

The LM903 uses the thermal-resistive probe technique to measure the level of nonflammable fluids. A low fluid level is indicated by a warning lamp operating in continuous or flashing mode. All supervisory requirements to control the thermal - resistive probe, including short and open circuit probe detection, are incorporated within the device. The circuit has possible applications in the detection of hydraulic fluid, oil level, etc., and may be used with partially conducting fluids.

Circuit Operation
A measurement is initiated when the supply is applied, provided the control input pin 7 is low. Once a measurement is commenced, pin 7 is latched low and the ramp capacitor on pin 12 begins to charge. After 25 ms when switch-on transients have subsided, a constant current is applied to the thermo-resistive probe. The value of probe current, which is supplied by an external PNP transistor, is set by an external resistor across an internally generated 21V reference. The lamp current is applied at the start of probe current.

35 ms after switch-on, the voltage across the probe is sampled and held on external capacitor C1 (leakage current at pin 1 less than 1 nA). After a further 1.5 seconds the difference between the present probe voltage and the initial probe voltage is measured, multiplied by 3 and compared with a reference voltage of 850 mV (externally adjustable via pin 16). If the amplified voltage difference is less than the reference voltage the lamp is switched off, otherwise the lamp commences flashing at 1 Hz to 2 Hz. 10 ms later the measurement latch operates to store the result and after a further 8 ms the probe current is switched off.

A second measurement can only be initiated by interrupting the supply. An external CR can be arranged on pin 7 to prevent a second measurement attempt for 1 minute. The measurement condition stored in the latch will control the lamp.

PROBES
The circuit effectively measures the thermal resistance of the probe. This varies depending on the surrounding medium (Figure 1). It is necessary to be able to heat the probe with the current applied and, for there to be sufficient change in resistance with the temperature change, to provide the voltage to be measured.

Probes require resistance wire with a high resistivity and temperature coefficient. Nickel cobalt alloy resistance wires are available with resistivity of 50 mXcm and temperature coefficient of 3300 ppm which can be made into suitable probes. Wires used in probes for use in liquids must be designed to drain freely to avoid clogging. A possible arrangement is shown in Figure 2.

The probe voltage has to be greater than 0.7V to prevent short circuit probe detection less than 5V to avoid open circuit detection. With a 200 mA probe current this gives a probe resistance range of 4X to 25X. This low value makes it possible to use the probe in partially conducting fluids.

Using resistance wire of 50 mXcm resistivity, 8 cm of 0.08 mm (40 AWG) give approximately 8X at 25ßC. Such a probe will give about 500 mV change between first and second measurements in air, and 100 mV change with oil, hydraulic fluid, etc., in the application circuit. With an alarm threshold of 280 mV (typ) lack of fluid can readily be detected. As the probe current, measurement reference and measurement period are all externally adjustable, there is freedom to use different probes and fluids.

Another possibility is the use of high temperature coefficient resistors made for special applications and positive temperature coefficient thermistors. The encapsulation must have a sufficiently low thermal resistance so as not to mask the change due to the different surrounding mediums, and the thermal time constant must be quick enough to enable the temperature change to take place between the two measurements. The ramp timing could be adjusted to assist this. Probes in liquids must be able to drain freely. (Datasheet)

Scriptable Thermometer and Vending Machine

noreply@blogger.com (Go2Media) — Tue, 27 May 2008 21:56:00 +0000

A unified thermometric controller that can be programmed with simple scripts, integrating the "classic" thermometer/controller pair.

You can build a variety of simple machines with the same hardware and a different script : a charting thermometer, a vending machine that dials your number when empty, a leavening cell

* thermometer with 1°F (0.5C) resolution

* four switch inputs, four relay outputs

* only an handful of cheap parts

* graphic LCD display

* script interpreter built-in, can run ASCII programs (basic-like)

* 6KB non volatile script memory

* full screen editor built-in

* modular C source code (need a graphic LCD driver?)

* Two applications provided:

CHARTING THERMOMETER

Load this script to make Scriptherm draw temperature graphs

SMS PHONE-MAIL ENPOWERED VENDING MACHINE

Load this script to control a refrigerated vending machine that sends you a SMS phone mail message when empty

Downloads: the contest entry with project all circuit details and source code; from the National Semiconductor's web site, or the PDF schematic only.

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River Level Monitoring System - RiverSpy2 #2

noreply@blogger.com (Go2Media) — Tue, 27 May 2008 21:36:00 +0000

How to get started

As you can see from the picture at part #1, the original system was prototyped using veroboard. If you are not familiar with electronics, you will find it easier to build using a printed circuit board (pcb). The layout files are given below. You can order from within the expresspcb program. The MiniBoard service at expresspcb costs US$83 for 3 boards, including a courier service to Ireland. You only need one pcb per gauge but it is not possible to order just one pcb. (If you have a spare pcb, please send it to Daithi Power, Electrical Engineering Dept, University College Cork, Ireland) Alternatively, if you have pcb making facilities of your own, use the express pcb software to print overlays and make a pcb yourself. The right hand side of the pcb snaps off to make the sensor board. The larger left side is used to make the controller board. The controller board measures 3" by 2.5". The sensor part is 0.8" by 2.5".

To assemble and test the circuit, you will need the following tools
* Soldering iron, solder and a small wet sponge to clean the iron
* A small pliers and a snips
* Multimeter for measuring voltages and testing connections

Electrical schematic is here

Bill of materials is here

PCB silkscreen is here

PCB layout is here View and order PCBs using the free software at www.expresspcb.com Three mini-boards cost $51 + shipping.

Assembly drawing of the layout

Sensor
Start with the pressure sensor end. Its the section in the dashed box on the first page of the schematic. Pictures of the construction are shown here. You will need a soldering iron, fine solder, a piece of vero board, a snips and a volt meter. Order the pressure sensor (26PCBFA6D), the INA122, and a small aluminium box from farnell. You will also need a 4m length of 1/4" plastic tubing and a long length of 3 core cable. The length of cable depends on the distance from the sensor to the solar panel at the river bank. Measure the distance with a throw-bag rope and add a few metres. I used shielded cable but ordanary house wiring cable should do fine. Solder the circuit together, power it with a 9V or 12V battery and measure the output using a volt meter. It should read about 0.1V normally and increase when you suck on the tube. If all is ok, put it in the box. You will have to drill holes in the box for the tube and cable. Use a separator to create a cavity for the open end of the sensor as shown in the pictures. Test the circuit again and then fill it with epoxy. Make sure nothing is shorted to the side and that epoxy doesn't get into the open end of the sensor. Test it again while the epoxy is wet by connecting a battery to the far end of the cable. If something has shorted, you will still have a chance to move things around. If all is ok, stick on the lid and let it dry. After it has cured, drop it in a barrel of water and pow er up the far side of the cable with your battery. If the signal voltage reads somewhere around 1.5V per metre of water, pat yourself on the back.

Before I potted the sensor with epoxy, I screwed the box to one end of a 0.5m length of stainless steel. At the other end of the steel, I drilled some 10m holes to allow me to bolt the sensor to the side of an existing stick gauge at the river bank. The distance between the sensor and 10mm holes allowed the sensor to be mounted under the water without having to drill any holes under water. The system should be installed while the river is at a very low level to ensure the s ensor always stays under water.

Pictures of sensor construction
Datasheets for the components can be found at Honeywell , Texas Instruments and Farnell

Controller
Order the controller components and solder them in. The PIC, PT6102 and the INA122 can be obtained as free samples. Look at the Bill of Materials to get order numbers for the rest of the components. Use an ic socket to mount the PIC. The Batt and Phone connectors have extra holes to either use terminal blocks or "Molex" connectors. I find Molex very convenient but if you don't have a crimping tool, go for the terminal blocks. Once assembled you will need access to a PIC programmer such as the ICD2. If you have no way of prorgamming it, send me a PIC and I'll program it for you. Program the PIC using the hex file below and the MPLAB softwar e that you can download from Microchip. During programming, the ICD2 needs to be connected to, and configured to use, an external 9V supply. If you're stuck, send me a PIC and I'll program it for you. Next power up the system using a 12V supply or a battery. The LED should toggle on and off every second.

Hex file for programming PIC is here

Phone

So far, I have built systems using the Siemens M35 and the C45. Any old Siemens phone should do but the connectors on the later ones have gotten smaller so it won't be as easy to solde r on the wires. The battery is removed from the phone and it is powered directly by the controller. The AT language used to talk to the internal modem is much the same for all Siemens phones. I have put some pictures of wiring an M35 here . The wire needs to be very fine. I used "wire-wrap" wire. It helps to put some solder on the wire before soldering to the phone. In the pictures shown, the red and black wires are soldered directly to the phone pcb. It is also possible (and easier) to solder them to the contacts that would normally press against the battery. Siemens also make a range of GSM modems su ch as the TC35. These are made for telemetry applications and would be easy to wire up but would cost you a lot more that an old phone.

Phone connector pin-out here

Pictures of phone wiring here

Installation
A picture of an early RiverSpy rev 2.0 controller is shown below. The latest version is a bit larger and uses through hold components instead of surface mount to make it easier for an inexperienced person to assemble. I'll put up some pictures of the latest rev later.

Terminal block for solar panel or external 12V supply
Molex Connector forattery (paralleled with connector 1)
Debugging interface can be used to monitor phone communications using a pc serial port
ICD2 interface for programming the PIC
Molex connector to mobile phone
Molex connector to underwater sensor

The controller, battery and phone should be mounted in a waterproof box. A plastic box allows optimum phone coverage but if vandalism concerns require the use of a metal box, then an external antenna or the phone may be required. A frame should be contructed to mount the solar panel and the box. To optimise solar energy in winter, the solar panel must face south, have a clear view of the sky and be inclined at 70 degrees to the horizontal. Once all of the components have been connected together, configure it as per the installation manual given below.
Send me an email if you need some help.

Installation manual is here

Debugging

I have also put up a schematic of a small circuit that I use for debugging here . All it does is convert a 5V-0V signal to a +12V-12V signal suitable for connecting to the serial port of a pc or laptop. It listens in on the communications between the control board and the phone. I normally connect it to the RX (receive) line of the PIC. RX and GND are at pins 5 and 6 of the connector J4. RX carries the data going from the phone to the PIC. The phone should echo the characters sent from the PIC to the phone so you should see both sides of the conversation. If this is not working, it can also be connected to the TX (transmit) line but this only shows the characters sent by the PIC. The characters can be displayed on the pc using hyperterminal set at COM1, 9600,N,8,1, no flow control. A similar circuit is included in a siemens pc data cable so if you have one of those, just disassemble the connector at the phone end and use that instead. The pinout of the phone connector is given here. Do not connect the TX of the data cable (pin6, RX of the phone) to the phone at the same time as connecting the TX from the PIC. (its like two people trying to talk using walkie talkies at the same time) Also note that pin 3 (Power) and pin 4 (Fbatt+) shown in the phone connector pinout are not the same as the positive terminal of the phone battery (BATT+).

Contacts
If you have questions, contact Daithí Power, visit page

River Level Monitoring System - RiverSpy2 #1

noreply@blogger.com (Go2Media) — Tue, 27 May 2008 21:29:00 +0000

System Overview
The diagram below gives an overall picture of the system. At the river end, the system is broken into two parts. At the bottom of the river, bolted to an existing stick gauge (or some other convienient location) is a differential pressure sensor. This sensor measures the difference in pressure between the athmosphere and the bottom of the river. To make this differential measurement , one side of the sensor is connected to a breather tube and the other end is open to the surrounding water. The pressure difference P=ρgh , where ρ is density, g is 9.81m/s2 and h is the height between the sensor and the surface of the water. The small signal voltage is amplified by an instrumentation amplifier chip.

The sensor board is connected to the controller board via a 3-core cable. One wire carries a 10V supply to the sensor board. Another wire carries the analog pressure signal back to the controller. The third wire is a ground. The controller board is mounted somewhere on the river bank, in a weather-proof box along with a 12V battery and an old mobile phone. A solar panel is mounted above the box so the location should have an unobstructed view of the southern sky. If vandalism is a concern, the system should perhaps be mounted on top of a tree or a high pole.

Every 15 minutes, the controller board powers up the sensor board and reads the signal once per second for thirty seconds. The measurements are averaged so that the reading is not affected by surges in the water level. Once the reading has been taken, it is stored in memory and the system goes into a low power mode until it is time to take the next reading. Once a day at 09:00, the 96 measurements taken the previous day are collated into a single sms message and sent to an email gateway. The email generated is read by a server which updates the wap and web sites.

The phone that I used is an old Siemens M35, but I think that the command set is the same for all of the M,C and S 25 and 35 phones. The phone does not contain its own battery. (The batteries in those phones were fairly bad anyway) Instead it runs from a supply taken from the 12V battery via a dc-dc converter.

When the system receives a phone call, it examines the caller id to see if an administrator is calling. If it is an admin, the system allows the remote phone to ring once and then hangs up. An sms is sent to the administrator containing the most recent level, the level from 30min previous, the level from 60 min previous and the current state of the 12V battery. If the caller id is not that of an admin, the system will answer the call and give a series of beeps to indicate the most recent level.

Controller board, phone, battery and solar panel mount
The photo below shows the original RiverSpy system with a controller prototyped on veroboard. RiverSpy 2 is laid out on a printed circuited board. The layout file is at the bottom of this page.

When admins ring the phone, the system declines the call and sends back a text of the level now, 30 mins ago and 1 hour ago. When others ring the phone, the system answers the call and gives a series of beeps to indicate the current level.

Next Page

VO Fuel Controller

noreply@blogger.com (Go2Media) — Tue, 27 May 2008 21:23:00 +0000

A small circuit to avoid cross contamination of diesel and VO in dual tank vehicles. This is a schematic for a vegetable oil fuel controller, the function is to enforce that VO goes back to the VO tank and diesel goes back to the diesel tank.

Notable Parts:
* K1 is the return fuel line relay
* K2 is the send fuel line relay
* S1 is the primary switch
* S2 is the bypass switch
* S3 is the purge button
* S4 is the On/Off switch
* LED1 is the return line indicator
* LED2 is the send line indicator (download schematic)

Usage
When the vehicle is warm enough so that it can run on vegetable oil turn on S1. The send line will immediately switch to VO and the return line will stay on diesel for a user specified amount of time. To determine correct timing switch your engine to VO and time how long it takes for the diesel to be purge from the system. Now you set the time in the circuit by changing R1 to the correct value based on 1.1 * R1 * C2. To make it easier, I set C2 at 1000µF, so if you want about 45 seconds use the closest value below 45Kohms (45,000 ohms). In the circuit as set up above R1 is 39K ohms giving a timing of just under 45 seconds (1.1 * 39 = 42.9).

When you are a few minutes from home turn off S1 and press S3. By turning off S1 you will switch the send line back to diesel and by pressing S3 you will keep the return line on VO for a user specified amount of time. To set timing use the same value resistor for R4 as you did for R1.

If you stop for a short period of time and the engine is still warm enough to run on VO when you restart it then either switch on S2 for a minute or so or press the purge button. In either case you will bypass the on-delay timer and keep the VO going to the VO tank.

Caveats
Do not expect exact timing from this circuit because capacitors are not perfect and voltage leakage will increase the time to some extent. When I timed the above circuit I found that it varied approximately 2 - 5 seconds (though I used a stopwatch and might have hit the start early or late, so YMMV). The timing can also be affected by length of time of discharge of the capacitors. If you turn off the circuit and turn it on again pretty quickly the timing can be much shorter than expected. I do not consider this an issue because the time it takes for the vehicle to cool down should be well longer than the time it takes for the capacitors to discharge. If this does become a problem use a lower value capacitor and a higher value resistor, for instance you can use a 220uF capacitor and a 180K ohm resistor to get approximately the same amount of time but the timing errors I initially stated may become more noticeable.

Modifications
If you want the circuit to be more automated so you can just switch it on when you turn on the vehicle and it will wait until temperatures are high enough before switching from diesel to VO, just add a thermostat into the circuit directly before S1. Use a NO (normally open) thermostat set to close it's contacts when the desired temperature is reached.
Parts List

* (1) 7805 voltage regulator
* (2) 1N4148 diodes
* (2) SPST switch
* (1) DPST switch
* (1) N/O momentary push button switch
* (2) LM555 timer
* (2) 1000uF polarized capacitors
* (1) 0.01uF non-polarized capacitor
* (3) 0.1uF non-polarized capacitors
* (2) LEDs
* (2) 500 ohm resistors
* (2) 100K ohm resistors
* (2) resistors chosen for timing value (R1 and R4)
* (2) solid state relays capable of handling the current your solenoid valves draw

All capacitors should be rated at least 25 volts, anything higher is fine.
Resistors should be rated for 1/4 watt.
7805 is a generic voltage regulator, if it says 78L05AZ or something it's still fine. visit page

Disclaimer & Terms Of Use:
This circuit is presented as is with no warranty of any kind, I can not be held responsible for any damages you incur either financial or otherwise. This design was created by Seth Koster and may not be used for profit. I hereby grant permission to use this circuit for personal use. Be sure to keep a careful eye on the circuit for a while after you install it to ensure that it is working properly and you installed it correctly. Please use safety equipment when working on electronics!

Fluid Level Sensor

noreply@blogger.com (Go2Media) — Tue, 27 May 2008 21:14:00 +0000

This Fluid-Level Sensor circuit uses an AC-sensing signal to eliminate electrolytic corrosion on the probes. The AC signal is rectified and used to drive Transistor T1 that drives the relay. The relay is a 12-V type of your choice.

Transistor T1 can also be a TUP. Check out the TUP/TUN document for a large selection of European transistors and what this system is all about. Diodes D2 and D3 are both small signal diodes (1N4148). Diode D1 (1N4001) eliminates transients and possible sparking over the relay coil. Do not use a signal diode for this but a rectifier diode like the 1N4001 or other types of the 1N400x series. Resistor R2 controls the sensitivity. Also your choice. Select one between 10 and 22 Mega-ohm, or use a trim-pot.

The MC14093B is a CMOS quad 2-input NAND Schmitt trigger. The supply voltage can be between 3.0 and 18Vdc. It is pin-for-pin compatible with the CD4093. The capacitors are standard ceramic types but try others if you have them available. (download schematic)

Parts List:

R1 = 470K N1,N2 = MC14093B
R2 = 15M* T1 = 2N3906 (these will work also: PN200, 2N4413)
C1-C4 = 2N2 (2.2nF) (NTE159, ECG159, BC557, BC157, TUP)
D1 = 1N4001 Ry = Relay (12V or matching supply voltage)
D2,3 = 1N4148 Sensor = Stainless Steel probes, brass, chrome, etc.

Please note:
Unused inputs MUST be tied to an appropriate voltage level, either ground or +12V. In this case, tie input pins 8, 9, 12, and 13 to either ground or +12v. Unused outputs (10 & 11) MUST be left open. You can use them as spares when needed.
In regards to the sensor, use your imagination. Stainless steel would be preferred but try other materials too. Depending on what type of fluid you use it for you naturally would choose your type of sensor which would resist corrosion for that particular fluid. I often use chrome bicycle spokes with very good success. The 'Sensor' works via the capacitive method.

The "RESET" switch in the circuit is optional. The relay can be replaced with anything you like; buzzer, lamps, other relays, etc.

Below are a couple valuable comments from Dave Burton of Burton Systems Software:

Thanks, Tony, for publishing your Fluid-Level Sensor design. I'm using it to detect sewer line plugs (water backing up toward the access port), and hot water heater / clothes washer / AC condensate pump overflows/leaks (water on the basement floor). It works very well.

Also, it says "the 'Sensor' works via the capacitive method." But I don't think that is correct. It would be more accurate to say that, for detecting fluids that are perfect insulators, the circuit CAN be made to work by detecting an increase in capacitance when the fluid replaces air in an air gap in the sensor.

But for the more common case of fluids that are not perfect insulators (like water on my basement floor), the circuit works by detecting resistive conduction through the fluid. It is lowered resistance that is detected, not increased capacitance.

To detect insulating fluids via the capacitive method would require good sized plates separated by an air gap, and careful adjustment of the sensitivity via R2 to distinguish between the possibly small change in capacitance due to the presence of the fluid. The difference might be small because there is only a fairly small differences between the dielectric constants of air and some common fluids. E.g., air has a dielectric constant of 1, and typical oils have dielectric constants of 2 to 5. Note, too, that desire to get a measurably large amount of capacitance leads us to desire that the gap between the plates be small (because the capacitance is inversely proportional to the distance between the plates), but the gap cannot be too small, lest capillary action hold fluid between the plates even after the fluid level has dropped below our sensor.

But to detect dirty water or tap water you can use almost anything: even a pair of bare wire ends several am apart works just fine.

Also, one handy feature not mentioned in the article is that several resistive "sensors" can be hooked up together (in parallel) to detect fluid at any of several different locations. visit page

Honeybee Traffic Counter

noreply@blogger.com (Go2Media) — Tue, 27 May 2008 21:12:00 +0000

This electronic circuit is a counter for honeybee traffic. The circuit designed similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive. The low power circuit uses a slotted opto-sensor to detect the passing bees.

The counter circuit advances an electronic counting module whenever a honeybee passes through the sensor. The device only counts the number of bees going through the sensor. A different circuit would be needed to count the number of bees only going out or only coming into the hive.

Go to Honeybee traffic counter in detail

Pyroelectric Infrared (PIR) Motion Sensor

noreply@blogger.com (Go2Media) — Thu, 08 May 2008 03:03:00 +0000

Infrared radiation exists in the electromagnetic spectrum at a wavelength that is longer than visible light. Infrared radiation cannot be seen but it can be detected. Objects that generate heat also generate infrared radiation and those objects include animals and the human body whose radiation is strongest at a wavelength of 9.4µm.

The pyroelectric sensor is made of a crystalline material that generates a surface electric charge when exposed to heat in the form of infrared radiation. When the amount of radiation striking the crystal changes, the amount of charge also changes and can then be measured with a sensitive FET device built into the sensor. The ensor elements are sensitive to radiation over a wide range so a filter window is added to the TO5 package to limit incoming radiation to the 8 to 14µm range which is most sensitive to human body radiation.

This circuit is from the GLOLAB web page. The document referenced here includes an excellent design as well as an excellent tutorial on PIR devices. You've probably seen these devices in homes and businesses and maybe wondered what they were. Now you can find out what they are, how they work, and how you can build one. We've seen PIR sensors assemblies featured in some of the low-priced surplus magazines that come through so these systems should be very inexpensive to build.

Download Documentation Manual - Visit Page

Economy Radar Detector

noreply@blogger.com (Go2Media) — Thu, 08 May 2008 02:57:00 +0000

This circuit uses a 1458 dual op-amp to form a radar detector. C1 is the detector of the radar signal. The first op-amp forms a current-to-voltage converter and the second op-amp buffers the output to drive the piezo transducer. R5 sets the switching threshold of the second op-amp; normally it is adjusted so that the circuit barely triggers on background noise, then it's backed off a bit. The response of the circuit may be tuned by adjusting the length of the leads on C1. For typical road-radar systems, the input capacitor's leads should be about 0.5 to 0.6 inches long.

The circuit on the following link seems to be fake. Detection/reception on GHz range requires the employment of specialized point contact microwave diodes (usually cartridge type) placed inside the resonant cavities with feed horn connected to the opening of cavity. I am surprised what this "Economy radar detector" detects with the open long leaded capacitor which can never ever be a replacement of any diode. Detection of radar signals, specially the police radars for vehicle speed detection requires highly sensitive input stages as the incoming signal is usually in the range of micro watts or below depending on the distance of radar and vehicle due to the inverse square law.

Remote Telephone Ringer

noreply@blogger.com (Go2Media) — Wed, 07 May 2008 10:05:00 +0000

This remote telephone bell ringer allows you to use a large (and loud) external bell in place or in addition to the built in (and rather wussy) ringer in most modern telephones. This is ideal for large outdoor areas, noisy shops or those hard of hearing. Most any large bell can be used as the circuit can be easily adjusted for various supply voltages.

Parts List
C1- 0.47 300V Capacitor
C2 - 47uF 25V Electrolytic Capacitor
R1 - 1K 1/4W Resistor
R2 - 10K 1/4W Resistor
R3 - 1K Pot
R4 - 2K 1/4W Resistor
Q1 - 6A, 200V TRIAC
Q2 - 6A, 200V SCR (106, Etc.)
D1 - 1N4774 Zener Diode
D2, D3- 1N4007 Rectifier Diode
U1- 4N33 Opto Isolator
Bell - Large Bell (Fire Bell, School Bell, Etc.)
Misc.- Board, Wire, Socket For U1, Case

Notes
1. Virtually any TRIAC and SCR will work for Q1 and Q2 as long as the voltage rating is high enough. Q2 needs enough current capacity to handle the full load of the bell.
2. To adjust R3, call the phone line on which the ringer is installed and adjust the pot until the bell begins to sound consistently.
3. Make sure to check with local authorities before you connect a homemade device to your phone lines. Some areas mandate that only approved devices can be connected to the loop. This circuit provides an opto-isolator to prevent cosstalk between the phone line and power supply as well as to avoid ground loops. visit page

Weather Satellite Receiver

noreply@blogger.com (Go2Media) — Wed, 07 May 2008 09:38:00 +0000

The days of guessing the weather by looking at the clouds overhead have just ended. Now you can look at the clouds from above! This project will allow you to receive pictures from satellites 600 km overhead. A typical NOAA satellite can cover nearly 1/16 of the earth in a single pass! In New York, we are able to clearly capture images from mid-Hudson bay (where there was still ice in late spring), all the way down past Cuba, as well as spanning from Wisconsin to far out in the Atlantic Ocean. The clarity of the image was enough to see the individual Finger Lakes (in New York), and shadows on the underside of thunderstorms.

This receiver allows you to receive weather satellite transmissions on the VHF band, where most of the polar-orbiting satellites are located. You will recognize these transmissions on the news when you see the time lapse of the clouds darting across the countryside. The weather man in this case has taken multiple images on the computer, aligned and pieced them together, and then run through one image after the other.

The way in which a weather satellite works is fairly simple. Just think of your office fax machine as an example. The satellites circle the Earth going north to south back to north again almost directly over the poles, which is why they call it a polar orbit. This means that the satellite will cover every location on the Earth at least twice per day. With a good antenna, and partly because of overlap of consecutive orbits, you can conceivably receive the same satellite up to six times a day! Notice though that the image received from polar orbits will be upside down on every other pass.

The satellite retrieves the data in a linear fashion, one line at a time using a
scanning radiometer. The scanning radiometer transmits the equivalent of a single television horizontal line as the satellite circles the earth. The system uses a series of optics and a motor driven rotating mirror system to receive a very narrow line of the image of the Earth. Each line is received at a right angle to the satellite’s orbital track, so as the satellite circles the earth, a line is received from west to east or east to west depending on the orbit of the satellite. The total image is received from north to south or south to north depending on the orbit also, and this motion is what relays the equivalent of the vertical scan in a television. You can continue receiving this satellite as long as it is within the line of sight.

Since all of the receivable satellites are similar, we will describe the ones you will most commonly receive. The NOAA/TIROS satellites, during the first half of the transmission, send visible light data to the receiver at the same time they are taking in the view. Meanwhile during the same part of the scan, they are recording the infrared view. During the second half of the scan, while the sensors are facing away from the earth, it sends the infrared data. The user then sees the data as two images side by side, on the left the visible light data is seen, and on the right, infrared data is seen. In between the images are synchronization pulses that help computers to align the individual lines precisely.

These particular satellites continuously transmit an FM signal modulated with a 2400Hz tone. This tone is very precise in frequency so the image seen is aligned properly. The 2400Hz tone is AM modulated with the intensity of the current view of the earth. The brighter or colder the point on the earth, the higher in amplitude the 2400Hz signal is.

The receiver demodulates the FM signal and retrieves the 2400Hz tone. The detector board in the computer will then find the peak amplitude of each wave of the 2400Hz tone, and each peak, upper and lower now represents a single pixel on the screen. For the NOAA/TIROS satellites, each horizontal line represents 2400 pixels, since the incoming frequency is 2400Hz, and the scanning radiometer rotates twice per second. The full 12 minute pass of a NOAA satellite requires approximately 3.5 MB (3.5 million 8 bit pixels) of storage! This is much more data (pixels) than can be seen on a super VGA screen at any one time. Manual Visit Page

Data Acquisition Using INS8048

noreply@blogger.com (Go2Media) — Wed, 07 May 2008 09:36:00 +0000

This application note describes techniques for interfacing National Semiconductor's ADC0833 serial I/O, and ADC0804 parallel I/O A/D converters to the INS8048 family of microprocessors. A hardware and software interface example is provided for each A/D, along with a brief theory of operation.

Since the INS8048 series microprocessors are single-chip, multiple I/O line, high speed devices designed as efficient controllers, the capacity to interface with analog peripherals is obvious. That the conversion be fast, inexpensive and easily expanded to accommodate a number of I/O devices is desirable.

The INS8048 is a self-contained, 8-bit processor in a 40-pin dual-in-line package. It contains its own system timing, control logic and memory. All parts contain RAM (64, 128, 256 bytes) and offer the option of on-board ROM (1k, 2k, 4k depending on part). It provides extensive bit-handling capabilities, 97 instructions, and offers easy expansion for I/O and memory. The ADC0833 A/D converter is an 8-bit successive-approximation device with serial I/O and conversion time of 25 ms.

This family of converters offers various configurations of multiplexed analog inputs which can be software programmed as single-ended, or as differential inputs, or both. Single-ended inputs are referenced to a common pin which is either referred to analog ground or to a fixed reference voltage. Like the INS8048 family, a single 5V power supply is all that is needed. The inputs will accept a 0V-5V range. No zero adjust is necessary. It is compatible with TTL and MOS at both input and output. The output can be selected as either MSB or LSB first. Visit Page

Making Printed Circuit Boards (PCBs)

noreply@blogger.com (Go2Media) — Thu, 01 May 2008 19:33:00 +0000

Creating Printed Circuit Boards (PCBs) is easy and fun for the whole family! But read the disclaimer -- heat and corrosive chemicals are dangerous. After you've prototyped and tested your circuit design, creating a PCB will provide a sturdy and reliable backbone for your circuit and will give your project a professional finished quality. Using PCBs can even help reduce the time you spend building circuits, especially if you are producing multiple units, as you only need to follow a parts placement diagram (there's no longer any need to worry about specific interconnections).

As is usually the case, there is more than one way to do it: there are numerous ways to create PCBs. They range from the time-consumming and difficult to the fully automated and expensive. Here we will attempt to describe a method we've found ideal for small production runs (say, a few prototypes to a couple of dozen--when you reach the hundreds, it will probably be easier, quicker and cheaper to outsource) of single- or double-sided boards.

Here is links for reference :
Assembly process the assembling process of sample circuit.
Chemical Etching Metals and Semiconductors.
Concepts of printed circuit design introduction to PCB technology.
Etching etching.
Etsen zonder fototechniek in Dutch
IC packages data handbook
Mounting and handling of semiconductor devices pdf file.
Photolithography photolithography.
Progressive wiring techniques
Surface Mount Technology Surface Mount Technology.
Surface Mount Technology pdf file.
Veroboard
Wire wrapping wire wrapping.
Wire wrapping how to wire wrap.

Stereo Encoder Oversampling For FM Transmitter

noreply@blogger.com (Go2Media) — Tue, 15 Apr 2008 12:18:00 +0000

Stereo encoder is the circuit that used in FM transmitter audio for a high quality stereo sound transmission. This stereo encoder produces an excellent crystal clear stereo sound and very good channel separation that can match with many more expensive stereo encoders that are available on the market.

Below is stereo encoder (stereocoder) from Katruud Electronic with improved PCB version 3.1. that use 8x oversampling multiplexer method

Download complete manual

Privacy Policy

noreply@blogger.com (Go2Media) — Wed, 19 Mar 2008 03:55:00 +0000

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Application of the MC1374 TV Modulator

noreply@blogger.com (Go2Media) — Thu, 13 Mar 2008 19:05:00 +0000

This application note presents the MC1374 TV modulator chip as a suitable device for applications where separate audio and composite video signals need to be converted to a high-quality VHF TV signal.

This TV modulator based MC1374 IC From Motorola with wide dynamic range and low distortion audio make it particularly well suited for applications such as video tape recorders, video disc players, TV games and subscription decoders.

The IC features:
* Single Supply, 5.0 V to 12 V
* Channel 3 or 4 Operation
* Variable Gain RF Modulator
* Wide Dynamic Range
* Low Intermodulation Distortion
* Positive or Negative Sync
* Low Audio Distortion
* Few External Components

View the datasheet - application note for more information.

FM AMPLIFIER SD1407 150 Watts

noreply@blogger.com (Go2Media) — Sun, 09 Mar 2008 09:13:00 +0000

This FM amplifier is originally designed by Broadcast Warehouse, based transistor SD1407 with redrawn schematic and redesigned pcb. You can drive the amplifier with maximum 1 watt input for 150 watts FM output.

Working frequency 88-108 MHz VHF band II, Power supply voltage 18-28 VDC.

Download : schematic, PCB all layer, top layer, bottom layer. More info ...

Splitband Audio Limiter

noreply@blogger.com (Go2Media) — Thu, 06 Mar 2008 16:06:00 +0000

This applicationis a very high specification peak control limiter. It has fast become the essential deviation limiter for FM radio
The application divided into two parts :

Broadband Limiter

Splitband Limiter

Active component : FET 2N5457 and Ics NE5534, 2N5532, TL071 TL072.

Download schematic and component mounted in Coreldraw 12 Format.

TV Transmitter Band I and III

noreply@blogger.com (Go2Media) — Thu, 06 Mar 2008 15:44:00 +0000

This TV transmitter working on VHF Band I and III, using negative sound modulation and PAL video modulation. This is suitable for countries using TV systems B and G, like Australia and Indonesia.

This circuit has not been tested at UHF frequencies. The modulated sound signal contains 5.5 -6MHz by tuning C5. Sound modulation is FM and is compatible with UK TV Transmitter System I sound. The transmitter however is working at VHF frequencies between 54 and 216MHz (band I and Band III) and therefore compatible only with countries using Pal System B and Pal System G. More info...

VHF/ UHF TV modulator Circuit

noreply@blogger.com (Go2Media) — Thu, 06 Mar 2008 15:34:00 +0000

Simple TV Modulator that working on VHF UHF Band, the oscillator generates frequency is modulated with the video signal and the modulated carrier wave thus generated is fed into the TV set's aerial input via a cable. Then all that remains to do is tune the VHF UHF TV set to the correct frequency.

Here's TV modulator circuit and see schematic for parts value

The harmonics generator converts the oscillator signal into a sort of frequency spectrum containing all the multiples of 27 MHz up to about 1800 MHz. The TV modulator's output signal is made up of a large number of little peaks, each of which is a complete transmitter signal. At least one of these will always be in band I (VHF channels 2. . . 4), one in band III (VHF channels S. . .12) and many of them will be in bands IV and V (UHF channels 21.. .69).

More info