Infra-Red Sensor/Monitor

Infra-Red Sensor/Monitor circuit diagramThe sensor/monitor shown in the diagram ‘wakes up’ the host system on detection of infra-red (IR) signals. It draws so little supply current that it can remain on continuously in a notebook computer or PDA device. Its ultra-low current drain (4µA maximum, 2.5µA typical) is primarily that of the comparator/reference device, IC1. The circuit is intended for the non-carrier systems common in infra-red Data Association (IrDA) applications. It also operates with carrier protocols such as those of TV remote controllers and Newton/Sharp ASK (an amplitude shift keying protocol developed by Sharp and used in the Apple Newton).

The range for 115,000-baud IrDA is limited to about 6 in (15 cm), but for 2400-baud IrDA, it improves to more than 12 in (30 cm). Immunity to ambient light is very good, although bright flashes usually cause false triggers. To handle such triggers, the system simply looks for IR activity after waking and then returns to sleep mode if none is present. The sensor shown, D1, a relatively large-area photo-diode packaged in an IR-filter material, produces about 60µA when exposed to heavy illumination, and 400mV when open-circuited. Most photo-diodes may be used. Operation is in the photovoltaic mode without applied bias.

This mode is slow and not generally used in photo-diode circuits, but speed is not essential here. The photovoltaic mode simplifies the circuit and saves a significant amount of power. In a more conventional configuration, for instance, photo-conductive, photo currents caused by ambient light and sourced by the bias network would increase the quiescent current about ten times.
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A multimedia thermometer of great visual impact.
  • The temperature is shown on an ordinary TV with crisp, full color graphics. Animation and sound can be easily added.
  • Pictures are recorded on a DVD or CD and can be varied according to the application.
  • Amazingly simple and cheap design (fits a $10 budget). Software tools are free. 
  • Modular, structured C code featuring a versatile Programmable Pulse Generator, an I2C-bus driver, and a RECS80 remote control transmitter 
  • Great for class experiments: it covers topics ranging from microcontrollers, programming languages, serial busses, sensors, remote controls, waveform generation, all the way up to the process of creating and preparing multimedia content. 
  • Another mind-provoking article published by Circuit Cellar magazine, and an award-winning design rewarded with the "Distinctive Excellence" prize in from the Motorola's "Flash Innovations" design contest.

The basic idea can be adapted to a variety of practical situations. The application as a public thermometer for hotels, malls, showrooms, stations, airports and tourist sites is straightforward. Thermometers per se are unquestionably useful, but the multimedia impact and low cost of the DVD-thermometer prospects new uses, especially when the possibility of adding advertisementsis considered.
Potential applications include talking “Please-take-a-number” displays, interactive product selectors (e.g. to select the right glue or paint, or to see how a new drill works), and colorful, dramatic displays for any sort of measurement.

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Infra Red Link

Circuit : Milan Markovic
Email  :

A basic Infra Red Link for audio communication for distances upto 3 metres.

IR Link

Ovo je shema jednostavne bez?i?ne komunikacije sa malo komponenata .Diode d1 i d2 su infracrvene le-diode ,a foto transistor je tako?er infracrveni radi ?to manjeg vanjskog utjecaja .Domet ure?aja je oko 3m no on se mo?e promijeniti brojem le-dioda i naponom koji se dovede na diode.Na izlaz se ?ak mogu i direktno spojiti slu?alice.Link mo?e poslu?iti i za prijenos drugih vrsta signala..Na popisu komponenata nema kriti?nih dijelova i izrada sklopa je jako jeftina. Uz malo pa?nje ne moe da ne radi.
P.S Transistors can be replaced with 2N3904 and 2N2222

In his circuit Milan has created a basic Infra Red transmitter and receiver. The transmitter comprises a single amplifying stage driving two series connected IR LEDS. The input source is connected to J1. Please note that the device will pass a small DC current through it and also directly bias the transistor. A suitable device is therefore a high output crystal microphone. These can produce high output voltages up to 1 Volt but this will be reduced by the transistors low input impedance.

The receiver is three stages, the first stage being a phototransistor. Stages two and three form a high gain darlington emitter follower, the bias for the whole stage derived through R2 and the phototransistor itself. C1 and R3 form a filter to reduce interference from flourescent lighting and other hum sources. The output is via Jack J2. Note also that the output device will pass a small DC current so a medium impedance loudspeaker or headphones are a good choice here.
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50MHz Receiver for the IR Detector


This project is about the receiver for my IR controlled transmitter.
The receiver works at 50MHz and is crystal controlled and will
receive and decode DTMF signals.
All contribution to this page are most welcome!

BackgroundThis receiver belongs to my IR-transmitter project.
To understand this receiver, I advice you first to read about the IR-transmitter.
This project will describe the receiver part I have made for the IR-transmitter. It is a 50MHz receiver based on the MC3371/MC3372 circuit. The circuit is a crystal controlled FM receiver. I have also implemented a dual gate preamplifier to gain sensistivity. This unit will receive and decode the DTMF codes from the transmitter. I have a DTMF decoder circuit MT8870 which will decode the incomming tones and finally a PIC16F84 is connected to the MT8870 to control the system and give sound alarms.
I will fresh up your memory about the 3 DTMF codes I use in the transmitter.

  • Code 19 : It has been a IR-detection.
  • Code 18 : "keep in touch" (sends every 10 second).
  • Code 17 : "beep" (Remote mode).
  • Click the pic to see a larger photo with the preamplifier shielded. Click the pic to see a larger photo with the preamplifier un-shielded.

    This receiver is small and portable. The power supply is a simple 9V battery.
    One problem with all receiver and transmitter is the antenna. Antenna size and performance is often opposite factors. An antenna (dipol) is quit large specially at 50MHz, but the performance will be much better than a short whip or helical antenna. This portable receiver use 75 cm wire as an antenna. It will give reasonable good reception and will not be too large in size, if you are nothappy with that, you could use a 9-element Yagi antenna if you want...*smiling*

    Block diagramBlock diagram for the receiver

    Most of this project has been explained in my other projects. The antenna is connected to a preamplifier based on a dual gate mosfet. The preamplifier will also match the antenna and the FM receiver circuit for best performance for the acutal frequency (about 50MHz). The FM-receiver will demodulate the incomming signal to a LF (audio) signal of 100mV. A DTMF circuit listen constantly to the LF signal and when a DTMF tone is present, the circuit will identify it and decode it to a digital number. A PIC processor will read the digital number and make action of the incomming code. The PIC will also make the beeping sound to alarm the user and also control the power to the unit.

    The advantage to use a DTMF circuit is because it is specially designed to decode the DTMF tone from the LF signal. The input LF-signal to the DTMF circuit can vary from 27.5mV to 869mV RMS which is quit good span.

    The filter in the DTMF circuit:
    The low and high group tones are separated by applying the dual-tone signal to the inputs of two 6th order switched capacitor bandpass filters with bandwidths that correspond to the bands enclosing the low and high group tones. The filter also incorporates notches at 350 and 440 Hz, providing excellent dial tone rejection. Each filter output is followed by a single-order switched capacitor section that smooths the signals prior to limiting. Signal limiting is performed by highgain comparators provided with hysteresis to prevent detection of unwanted low-level signals and noise.
    Conclusion: The DTMF circuit is outstanding to recover the data from a bad signal.

    SchematicClick on the pic to see a larger photo!

    Click on the pic to see a larger photo!Lets have a look at the schematic. Most of the component I use are surface mounted, that is why you can't see all of them on the photo. The antenna is connected to coil L1 at a tap point (se fig at right). This is to match the impedance. With good match the input filter L1 and C1 will be narrow and reject all unwanted frequency. The input is connected to gate 1 at the dual gate mosfet BF990A. You can use any dual gate fet as long as it has good gain. BF991 or BF981 will work good as well. Gate 2 is connected to half voltage to set the gain. At the drain of the fet, you will find L2 and C2 which is a tuned filter, and this filter also has the same function as the input filter. It will also impedance match the input to the radio circuit. L1 and L2 are not difficult to make. Just make 10 turns around a drill with 7.2mm diameter,and tap it at 2/3 from the cold side. My test has show that this will give good performance. You can of course experiment yourself with different tap points and check which will give the best performance. If you tap L1 closer to the cold side you will make it more narrow, and that can make it difficult to tune. see my Front end design of antenna page to understand why. When the preamplifier is finished you should shield it in some way or else it might not work good. I have build a box of Cu and drilled 2 hole where I can put a ceramic screw driver to tune C1 and C2. Without shielding the preamplifier will detune and be sensitive for hand effects.

    Receiver part:
    The FM-receiver is a basic MC3371/3372 circuit. It has everything you need to build a receiver. A crystal is oscillating at pin 1 & 2 and there is a coil (0.47uH) to make sure it oscillate at third overtone. Before the mixed signal is demodulated, it passes a 455kHz ceramic filter . I have found mine in an old cordless phone. Finally there is a quad coil which demodulate the IF and brings out the LF (DTMF tones) at pin 9.
    Pin 13 is the RSSI output (Relative Signal Strength Indicator) which give you voltage of how strong the RF signal is. I have connected a LED-voltmeter to this output when I tune the receiver. You can read more about this in the tuning section.

    DTMF part:

    This circuit doesn't need much components to work. It need an input frequency of 3.579545MHz, and It need a resistor R1 and C3 to set the time constant to detect a valid input DTMF tone. I will explain how it works. The pin 15 is called Delayed steering output (StD). If the DTMF-circuit detects a DTMF input tone, it will start to charge C3 through R1. When the level has reached a predefined level the StD output will go high indicating that there is a valid input DTMF tone, which can be read by the PIC. If the input DTMF tone no longer exist, C3 will discharge and the StD will go low again. By choosing the values of R1 and C3, you can define how long the input DTMF signal has to be, before the circuit accept it. In my transmitter I send the first key during 50mS and then i have a pause of 50mS and finally the last key for also 50mS. By choosing R1 to 300k and C3 to 100nF, the DTMF circuit want the signal to be at least 30 mS befor it accept it and set the StD high. You can read more detalied info about this in the datasheets. If the StD-time is set to short, the circuit might trigg StD on noise and if you set it too long (longer than 50mS) the circuit will never trigg.

    You may find this receiver too complex with PIC-cpu and DTMF and all.
    I have added this extra to this receiver just to make it possible to send several commands to the receiver and to obtain a reliable communication. I use only two digit in my transfere, but you can use as many as you want. (Example if you use 8 tones you will have 100 milion combinations) such transfer would take 800ms.
    By using DTMF, the radio system will not be so sensitive to noise. With this concept you can use the same frequency for several receivers, you only need to have different ID-number for each receiver.

    Power supplyWhen the ON/OFF button is pressed the power will flow through the diod (1N4148) and into the 7805 regulator which will provide the PIC with power. As soon as the PIC wakes it will set RB6 high which will make the NPN and the PNP transistor saturate and the power will continue to flow. The input RA1 probe the status of the ON/OFF button and if this button is pressed again, the PIC will beep and let RB6 go low, which will cut the power to the unit.
    I can now use one button to switch ON/OFF the receiver.

    TuningThis receiver need some tuning to work well.
    The preamplifier has a tuned LC circuits. L1 and C1 tunes the antenna (wire about 75cm) to receiving frequency. L2 and C2 should also be tune to receiving frequency and to give best receiving signal and less noise. The easiest way is to shield the preamplifier and drill 2 holes so you can tune the two capacitor. It is important to have good shileding, else it will detune and not work properly. I have build a portable audio amplifier and I use it to tune the preamplifier by conecting the output from the receiver pin9 to the audio amplifier. I can now hear the DTMF signal and it then I walk away some hundred meter from the transmitter and tune the preamplifier until I get the best performance.

    How to connect an external audio amplifier to the receiver to listen to the DTMF tones.One important thing to remeber is that if you connect a wire to the receiver, for example to the audioamplifier I explained above, you will change the groundplane size and you will tune the unit with the new groundplane. When you have tuned the unit and you disconect the wire, the groundplane change again and the unit will be detuned. What you should do in this case is to connect a 5k serie resistor in the ground wire and a 5k serie resistor in the signal wire, befor it is attached to the receiver unit (See fig at right). The total impedance will be 10k and the ground plane of the receiver will not be affected of the audio amplifier I have connected to hear the signal.
    When I did my test I soldered the two 5k resistor direct on the PCB of my receiver.
    You should also tune the quad coild for best audio receiving!

    Download PIC16F84 program (INHX8M format)
    ir_rec.zipReceiver program, the file is zipped!)
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    40khz IR tester


    40khz IR tester

    R1270 ohm resistor
    L1Visible LED
    S1On/Off Switch
    IR ModuleSharp GP1U5X IR Detect Module (or compatible)

    Use this circuit to test if the light coming from your 40khz IR emitter is really emitting the right frequency. The schematic says to use a GP1U5X ir module, but probably any 40khz detector module will work.. I used a GP1U26X module.
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    Variable 3 - 24 Volt / 3 Amp Power Supply


    This regulated power supply can be adjusted from 3 to 25 volts and is current limited to 2 amps as shown, but may be increased to 3 amps or more by selecting a smaller current sense resistor (0.3 ohm). The 2N3055 and 2N3053 transistors should be mounted on suitable heat sinks and the current sense resistor should be rated at 3 watts or more. Voltage regulation is controlled by 1/2 of a 1558 or 1458 op-amp. The 1458 may be substituted in the circuit below, but it is recommended the supply voltage to pin 8 be limited to 30 VDC, which can be accomplished by adding a 6.2 volt zener or 5.1 K resistor in series with pin 8. The maximum DC supply voltage for the 1458 and 1558 is 36 and 44 respectively. The power transformer should be capable of the desired current while maintaining an input voltage at least 4 volts higher than the desired output, but not exceeding the maximum supply voltage of the op-amp under minimal load conditions. The power transformer shown is a center tapped 25.2 volt AC / 2 amp unit that will provide regulated outputs of 24 volts at 0.7 amps, 15 volts at 2 amps, or 6 volts at 3 amps. The 3 amp output is obtained using the center tap of the transformer with the switch in the 18 volt position. All components should be available at Radio Shack with the exception of the 1558 op-amp.
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    An Amplified Zener

    The Circuit is not an Original design by me, but very useful.
    Revised: "Feb 23 2007"

    But it is Definately a good idea for some applications and I thought I would make
    it available to those persons not familiar with this method of Voltage Regulation.
    One application is where you need a Higher Power Zener, Possibly even a 100 watt rating.
    Another useful application is as a Shunt Regulator for Solar Cells that are used
    to charge "Lead Acid Batteries". Simply Place it in parallel with the Solar Cell
    and use Diode De-coupling between it and the battery.
    A 13 volt Zener diode will work well for charging a 12 volt battery on Standby use. Or use a 14 volt zener a diode for a Standard 14.6 volt charge.
    The Output voltage of this Amplified Zener is the "Zener Voltage" PLUS the "Emitter to Base Voltage" (Typically about .6 volts) Therefore a 14 volt zener will result in a 14.6 volt Amplified Zener.
    Adding a 1N4005 or a 1N4148 diode in series with the zener will increase the voltage by about 0.6 volts. A 1N5819 Schotkey diode will increase the voltage by about 0.3 volts.
    While most NPN Power Transistors will work, Higher Gain Transistors will give a much tighter "Knee Voltage". (better voltage Stability than any zener by itself)
    CX is Optional. It greatly reduces noise, but in a simple solar cell charging circuit, it isn't needed. The Capacitance effect of "CX" is also GREATLY Amplified by the transistor. In Operation the Zener in this circuit will typically only dissipate about 75 mW, so any 250 mW (or greater) zener is acceptable.
    NOTE: Zener Diodes are usually available in tolerances of 5%, 10% and 20%. A 12 volt Zener, with a 20% tolerance can be anything between 9.6 volts to 14.4 volts. That is a Huge Variation and can Greatly affect your results.
    "Back to My HOME Page"

    "This circuit can be used as if it were a powerful zener"

    "This is the Circuit for charging a Lead acid Battery"
    NOTE: This is Not really Practical for Charging NiCads or NiMh Batteries.
    These types of batteries require a different type of regulator to protect them from overcharging and heat damage.

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    This circuit will convert a standard relay to a pulse relay; pressing the button will switch it on and pressing it again will switch it off. For this purpose you need a relay with 2 sets of contacts: one is used for the circuit and the other is available for an outside circuit. Sometimes it is difficult or impossible to find a stepping relay, normally used in electrical wiring, and this is a viable solution. The relay used in this circuit was a power relay with 10A contacts and a coil resistance of 28Ω. The circuit will draw no power when idle and it is possible to scale up the circuit to operate at a higher voltage. The relay must be always rated at half the supply voltage, in our case it is a 6V relay for a 12V supply. The resistor in series with the coil must have a similar resistance as the coil or slightly higher and the other resistor should be twice the coil resistance. All capacitors are 25V. The capacitors value depends on the coil resistance: the higher the resistance the lower the value. As it takes a certain time to charge the capacitors it is necessary to wait about 0.5-1sec between one operation of the push button and the next. An unregulated 12V power supply is adequate for this circuit. 
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    Full short-circuit and overcurrent protection is given by this circuit suitable for workbench applications in technical schools and laboratories where there is a need to work directly with the mains. Additional features are a clearly visible red lamp indicating that the voltage is present, good isolation of the output circuit when the unit is off, only a few millivolts were measured with no load, current threshold adjustable over a limited range and the possibility of remote cutout: the 6V from the secondary can be taken anywhere, normally where you are working, even far away from the protection circuit. Pressing the push button will short-circuit the winding and the circuit will switch off thus removing the mains voltage. A suitable led is placed together with the push button to show whether the circuit is in operation or not. Additional remote cutout circuits can be wired in parallel if so required. The circuit will switch off if a short is applied at the output without blowing the fuse but it will blow if you try to activate the circuit if a short is already present. If in doubts, first activate the circuit and then apply the load. The BTB12-600SW is a snubberless triac while the T0805 is a standard triac: you may use other equivalent types but because of the way triacs are driven you cannot use, in this circuit, a snubberless triac instead of a standard triac and viceversa. The 250 μH inductor is a coreless inductor made with 100 turns of 1mm enamelled wire over a form 27mm diameter and 12mm wide. The mains transformer is a standard transformer with split primary wired in such a way that the circuit will self-sustain once it is activated. The same circuit was implemented with a current limit between 0.1 and 0.3A. In this case you have to change the fuse from 6.3A to 1.5A and the sensing resistor from 1Ω  to 10Ω. This resistor must be the cemented type not the armoured type. The latter is not able to withstand the temporary high overload that takes place during a short-circuit condition. Voltage drop from input to output is between 1V for little or no load and 3.6V with a load current of 2A.
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    Checking the status of your car battery (accumulator) should be easier with this circuit which measures the internal resistance of the battery. Pulses generated by the 555 are used to drive a dummy load and the AC voltage which develops across the battery gives an indication of its internal resistance: the lower the voltage the healthier the battery. The AC voltage is read out by means of a digital meter connected at the output. Separate leads are used for the dummy load and for the metering circuit. They should be connected to their respective battery lugs but they should not touch each other. This avoids erroneous readings due to less than perfect contacts of the dummy load. The internal resistance depends on the battery temperature as well; this is the reason for the switch:hot means a battery (not ambient) temperature between 35 and 52 degrees Centigrade, normal is for a temperature between 16 and 34 degrees and cold is good for a temperature from -4 to 15. Beyond these ranges the reading is unreliable. The internal resistance depends also on the rated capacity of the battery. The 100 ohm potentiometer sets the battery capacity: it is rotated totally to positive for a 100Ah battery and totally to negative for a 32Ah battery. A dial with uniform markings from 32 to 100 was used in the prototype. This means we can measure internal resistance of batteries rated from 32 to 100Ah. As there are a number of smaller 12V batteries around, specially for alarm systems, a switch was introduced that, in the X1 position, will change the capacity range to 3.2 - 10Ah. The unit has six leads going out of the box: two for the dummy load, two for the metering section and two going to the digital meter. Operation is simple: set the range, temperature and battery rating, then connect the dummy load and the metering leads to the battery lugs and read the ac voltage: you should be safe if it reads below 10-12mV otherwise it is better to give the battery a good recharge and if it is still beyond 10-12mV then probably you need a new battery. A bright orange LED shows that the unit is connected and in operation.
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    single transistor is all you need for this simple inverter. The main aim of this circuit is to provide a suitable supply for all kind of low power battery chargers that normally connect to the mains such as mobile phones, electric shavers, etc, even an electronic neon light rated at 5W was successfully connected. Only easily obtainable components are used. The transformer is a standard 10VA mains transformer with two 6V windings connected as shown in the schematic. Frequency of operation is between 70 and 190Hz depending on the nature of the load. This frequency is acceptable by most devices but obviously it is not suitable to drive frequency dependent appliances such as clocks or small motors that depend on the mains frequency in order to operate reliably. The transistor will not require any additional heatsink if it is assembled on the metallic case provided for the inverter. The neon glow light will give a useful indication, and warning, on the presence of a dangerous voltage at the output. A 2.5A fuse on the input supply line would be a useful addition. Operation is simple: switch on the unit and connect the load keeping an eye on the neon glow light which should be always on: certain switching chargers demand an initial peak current effectively shorting the output and switching off the neon: in this case you have to try repeatedly to connect the load until it works. A temporary short at the output and a temporary voltage reversal at the input will not damage the unit. Efficiency was not a design parameter however it was measured to be between 50 and 60%. If you have a 110V mains transformer and consequently a 110VAC output you should change the 0.1μF capacitor to 0.22μF, 400V. The waveform is only vaguely sinusoidal. Invert the connection of one of the 6V windings if oscillations do not set in
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    This circuit was specifically designed to recharge alkaline cells. The unusual connection of the transistor in each charging unit will cause it to oscillate, on and off, thus transferring the charge accumulated in the capacitor to the cell. The orange LED will blink for around 5 times a second for a 1.37V cell. For a totally discharged cell the blinking is faster but it will decrease until it will come to a stop when the cell is charged. You may leave the cell in the charger as it will trickle charge and keep it at around 1.6V. To set the correct voltage you have to connect a fresh, unused cell and adjust the trimmer until oscillations set in, then go back a little until no oscillation is present and the circuit is ready to operate. You should use only the specified transistors, LED colors, zener voltage and power rating because they will set the final voltage across the cell. A simple 9V charging circuit was also included: it will charge up to around 9.3V and then keep it on a trickle charge: the green LED will be off while charging and will be fully on when the battery is close to its final voltage.
    A 2.5VA transformer will easily charge up to 4 cells at the same time although 2 only are shown in the schematic. In order to minimize interference from one circuit to the other they have nothing in common except the transformer and, in order to show a balanced load to the transformer, half of the charging units will use the positive sinewave and the other half the negative sinewave. Make sure to use high beta transistors such as BC337-25 or better BC337-40. Given the dispersion of the transistor parameters it might happen that oscillations do not take place. Use a slightly higher zener voltage: 7.5V instead of 6.8 or a green led in place of the orange ones.
    All types of alkaline cells can be recharged: it will take 1 day for a discharged AA cell or 9V battery and up to several days for a large D type cell. The best practice is not to discharge completely the cell or battery but rather to give a short charge every so often although admittedly this is not easy to achieve. Do not attempt to recharge a totally discharged cell or a cell showing even the slightest sign of damage, best recharge is achieved when the battery is still 70% charged. The more the battery is left to discharge the less effective will be its recharge.
    I tried successfully to recharge NiMH cells as well. Although the charging profile for these cells is quite different from alkaline cells, the circuit seems to work fine provided you do not leave them in the charger forever, because of the possibility of overcharging especially for the smaller batteries.
    The mains transformer must be suited for the voltage available in each country: usually 230Vac or 115Vac.
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    The Adjustable Voltage Regulator


    Many amateurs have stopped by their local Radio Shack store and have noticed the famous LM317T adjustable voltage regulator. But, did you know that all voltage regulators are adjustable? Yes, any IC voltage regulator can be adjusted to a higher voltage than its fixed voltage by just adding a couple of resistors.
    As an example, lets consider using the popular 7805 (5 volt) voltage regulator as a 12 volt regulator. In figure 1, lets assume 470 for R1 which means that a constant current of 10.6 mA will be seen between terminals 2 and 3. This constant current plus a regulator standby current of about 2.5mA will flow through R2 to ground regardless of its value. Because of this constant 13.1 mA, R2 can now be set to a value which will give us a constant 7 volts across this resistor. A resistor value of 533 ohms or 510 (standard value) will give us the necessary 7 volts. With 5 volts across R1 and 7 volts across R2, a total regulated value of about 12 volts will appear across terminal 2 and ground. If a variable resistor is used for R2, then the output voltage can be easily fine tuned to any value greater than 5 volts. The regulator standby current will vary slightly in the 7805 but 2.5mA will yield good results in the calculations. If an exact voltage (within .3 volts) is needed then R2 must be a variable resistor.
    To make any fixed regulator adjustable, use the following formula:
    Vout = Vfixed + R2(Vfixed/R1 + Istndby)
    Vout=Desired output voltage
    Vfixed=Fixed voltage of IC regulator (5 volts for 7805 or 1.25 volts for LM317T)
    R1=Assume any value from about 470 to 1K for best results
    Istndby=Standby current of regulator (use 2.5MA for 7805 or zero for LM317T)
    Common Resistor Combinations for the 7805 regulator:
    6 Volts470100
    8 Volts470220
    9 Volts470330
    12 Volts470510
    Incidentally, the famous LM317T adjustable regulator is really nothing more than a fixed regulator with an output voltage of 1.25 volts. Amateurs seldom need voltages below 5 volts so the 7805 regulator is a good choice and it even costs a little bit less than the LM317T.
    DE N1HFX
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    Post title5 volt power supply:


    5volt power supply
    click here to enlarge the schematic

    U1LM7805 +5 VDC Voltage Regulator
    BR14 amp bridge rectifier
    T112.6 volt, 1.2 amp ac transformer
    F12 amp slow-blow fuse
    S1SPST toggle switch
    R1270 ohm resistor
    C13,000 uF electrolytic capacitor, 35 volt min.
    C2100 uF electrolytic capacitor, 35 volt min.
    LED1Light Emitting Diode
    MISC.fuse holder, heat sink for U1, binding posts, ac cord with plug, chassis

    all resistors are 5 or 10 percent tolerance, 1/4-watt
    all capacitors are 10 percent tolerance
    Please operate caution when building this power supply. It is run on, I believe, 120v ac current (standard US wall outlet) - and under the right circumstances 120 ac can kill you. Use a plastic enclosure if possible to decrease chances of short-circuiting. Don't use the power supply if it's wet, and never run it without the specified fuse.
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    PIC Harmonic Distortion Meter


    Wichit Sirichote,
    Build a simple instrument that measures the quaility of AC voltage with PIC project board.

    The 3rd harmonic distortion meter has been designed for measuring the quality of AC supply. The meter is built with aPIC18F2550 project board and the full wave rectifier front-end circuit. The AC power line, 220VAC is measured through the step down isolation transformer. The input signal to the 10-bit ADC is full wave rectified. The software performs DFT calculation finding the amplitude of the fundamental frequency and the 3rd harmonic. The distortion is computed by the ratio of the amplitude of the 3rd harmonic to the fundamental frequency. The meter has been tested with the square wave signal resulting 33% distortion. For low voltage AC utility, 220V, the reading showed approx. 3%. The meter can be applied for high voltage application with the appropriate signal conditioning.
    Figure 1: PIC Harmonic Distortion Meter
    Nowadays an increasing of the electronic devices having nonlinear characteristics are many used at home and office. Such devices mostly are computer based equipment with a low power factor switch mode power supply. The input circuit of the power supply uses a diode-capacitor at the front-end circuit. The current drawn is charging capacitor only near the peak voltage. Thus for a given feeder having finite impedance, there will be a lost from voltage dropped near the peak voltage resulting flattened top distortion of the AC voltage. To measure how high the distortion of AC voltage is, we may decompose it into the summation of sinusoid waves using DFT. The PIC harmonic distortion meter shows a method for finding the amplitude of the fundamental frequency and the 3rd harmonic. The reading shows percentage of the 3rd harmonic distortion.

    Figure 2: Flattend top AC voltage caused by a low power factor switch mode power supply.

    To measure the waveshape distortion, we use the quantity of the Total Harmonic Distortion, THD (equation 1). THD is the ratio of the power of harmonic components to the power of fundamental frequency. Our concern is the voltage distortion, we can just find the sum of the rms of the harmonic components, Vn and the rms of the fundamental frequency, V1.

    Most of the harmonic problem is caused by the 3rd component. Since the 3rd harmonic is the 2nd highest energy from the fundamental component. So we interest to find only the 3rd harmonic distortion using equation 2.

    We may decompose the periodic waveform, f(t) into the summation of a number of sinusoids waveform easily using the Discrete Fourier Transform (equation 3). A0 is the amplitude of DC components. For AC voltage waveform, A0 is zero.

    The amplitude for each harmonic can be computed from equation 4.
    The coefficients Bv and Cv for each harmonic are easily calculated by multiplying the corresponding sine wave and cosine wave to the input signal respectively (equation 5 and 6). Where delta t is time between sample, T is period, Vy is input signal.
    Since the AC signal has symmetry between positive cycle and negative cycle. We can find the harmonic component by capturing only half cycle. This reduces computing time by half.
    Input Circuit for PIC Project Board
    The hardware of the PIC Harmonic Distortion Meter is a the PIC18F2550 project board with the input circuit that receives AC signal from the isolated transformer. We made it with bridge diode and 20k voltage divider to provide a signal range for 0 to +5V ADC input of the PIC chip.
    Figure 3 shows the sample of input data for DFT calculation. The ADC data is 32-point 10-bit resolution.
    Figure 3: The 32-point sample half period AC input signal (see the flatten top).
    From equation 5 and 6 we will see, it is very easy to find the coefficients Bv and Cv for the fundamental frequency and 3rd harmonic. The software provides sine and cosine data for 50Hz and for 150Hz. The method is to find correlation between input signal and the sinusoid wave shape for 50Hz and 150Hz.
    Figure 4: The 32-point sine data for fundamental frequency and 3rd harmonic.

    Figure 4: The 32-point cosine data for fundamental frequency and 3rd harmonic..
    Testing with Input AC Signal
    The testing shows the input signal and 3rd harmonic detector (shown in THD) for a clean sine wave, square wave and the university AC plug.
    Figure 5: Clean sine wave, 3rd harmonic distortion <0.5% (no harmonic, shown only fundamental frequency).
    Figure 6: Squarewave, 3rd harmonic distortion ~ 33%.
    Figure 7: Distroted University AC plug, 3rd harmonic distortion ~ 4%.

    Figure 8: Demonstration of the 3rd harmonic meter to the students on the Science Day 2550.

    We built a cheap instrument for measuring the 3rd harmonic of AC power line with PIC18F2550 microcontroller. The software performs simple DFT calculation finding the amplitude of fundamental frequency (50Hz) and the 3rd harmonic (150Hz).

    Source codeDFT.c
    Hex fileDFT.hex

    2nd version with alarm and overload indicator
    The 2nd version firmware has been developed featuring the alarm and overload signal input indicators. Figure 9 shows the power on text message.
    Figure 9: Power on text message, "Power Line 3rd Harmonic Meter".

    As shown below, the first line is the amplitude of the fundamental frequency (50Hz). And the 2nd line is the 3rd harmonic amplitude. The Harmonic Distortion (HD) is displayed as HD=7.3%. When the distortion factor is over 5%, (as shown 7.3%) the symbol X will blink.
    Figure 10: The X symbol indicates the 3rd harmonic distortion is over 5%.
    If the signal input is overload, resulting the clipped waveform, the ov symbol will be indicated. We can slightly adjust the POT until the ov disappeared.
    Figure 11: The ov symbol indicates the signal input is overload.
    The signal input for DFT calculation can be only positive cycle (symmetry property), so we can use the bridge diode to provide full wave rectified signal and the voltage divider to provide proper level for ADC input.
    Figure 12: The small transformer provides safety isolation for student and the 9VAC input signal.Figure 13: The front end circuit is built with T1, isolation transformer, D1 bridge diode and R1 variable resistor. R1 is simple voltage divider providing 0-5V full-wave signal.
    Source code (50Hz AC power line)DFT.c
    Hex file (ready for PICkit II programmer)DFT.hex
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    3.3V / 5V Regulated Power Supply Circuit

    This circuit can be used to power your digital breadboard circuits.


    A very simple breadboard power supply that takes power from any DC wall wart that has a voltage of 5 to 10 volts and and then outputs a selectable 5V or 3.3V regulated voltage.




    • SW2 changes the output voltage from 5v to 3.3v.
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    200 Watt Modified PC Power Supply 13.5 Volt 14 Amp


    I got two old PC powersupplies for free, to be used for this test..
    They are named DTK Computer model PTP-2008. 200 Watt Output.
    Original outputs are:
    +5V 20A
    +12V 8A
    -5V 300mA
    -12V 300mA
    After modification:
    +13.5V 14Amp cont. 20 A for 20 sec.

    The external 230 Volt AC power ON/OFF switch is removed and bypassed.
    Old unused outputs are removed. Over voltage protection changed to only protect one output at 16 V,
    Voltage regulating resistor net changed to only monitor a single output,
    Do it like this:
    Cut: white, orange, blue, and yellow wires as close as possible to the pcb.
    Cut: all plugs away in the other end of the black and red wires, parallel all red and black wires..
    Desolder: Fan wires, L1, L3, L4, R25, R26, R27, R29, R50, R51, R52, R61, R66, D10, D16, D17, C29, C28, ZD1
    Mount a 680 Ohm 1/4 Watt at R50 location.
    Mount solderpins in the holes for R26, R61 and Fan connection.

    This is a fast part-drawn schematic that only covers what I wanted to know.
    Mount 13.5 K Ohm at the solderpins at R26. (13.5 Volt output adjust point)

    Mount 15 V Zener and 100 Ohm in series in the ZD1 holes. (Over voltage protection)
    If two or more powersupplies needs to be paralled, then cut R30,
    now it is possible to enter constant current mode opperation without shutting down.
    This is also needed if your load (or radio) has big capasitors in parallel with the power supply line.

    Orange wire connects unused cap to the new 13.5 Volt output (old +5 Output).

    Transformer low voltage outputs are cutted,
    and 12 volt output vindings are connected to the high current double diode.

    The fan is reverse mounted so that it will blow cold air into the heatsinks and transformer.
    The NTC is glued with epoxy to the heatsink with the powerdiode,
    The fan controller is changed so that the fan starts to rotate at +40 C on the heatsink,
    If the temperature goes further up, the fan will rotate faster.

    Mount potentiometer 47 K at R61 solderpoints. (adjust to fan start at 40 C then change to normal resistor)
    Output ripple is under 5mV pp at 20 Amp. (0 - 100 Mhz)
    I have tested it with my HF VHF and UHF rig, and could not hear any more noise than usual.
    Output power has been tested with 14 Amps cont. for one hour, no problem at all !!
    Efficiency at full max load is 60 %
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