- LOW POWER 12,000-VOLT POWER SUPPLY
If you need about 12,000 volts DC for an ion generator this circuit might be the ticket. It draws power from the 120vac power line but it uses a small 6KV camera flash trigger coil. The output signal is isolated from the power line. Although the circuit can only deliver about 5uA of current it can produce dangerous shocks, so be careful. - MINIATURE ISOLATED AC/DC POWER SUPPLY
This circuit uses a novel approach to produce a fully isolated and regulated 5 volts @30ma from the 120vac power line. It uses two tiny SCRs that alternately discharge two capacitors through a miniature high frequency transformer. The voltage spikes produced through the transformer are rectified, filtered and regulated. A very common 8-ohm audio impedance matching transformer can be used for the transformer. Published in EDN, Feb. 17, 1992 - Simple Security Wire Loop Alarm
A wire is looped through various objects which are to be monitored. The loop wire is typically an aircraft cable but could also be any insulated stranded wire. The loop is attached to a table or desk. Should the loop be cut, the alarm is sounded.
· ELECTRIC FIELD DISTURBANCE MONITOR-1
This schematic is the power supply and front-end sections of the field monitor that is discussed in more detail at Electric Field Disturbance Monitor. The system can detect human and animal motion by the electric fields they disturb.
· ELECTRIC FIELD DISTURBANCE MONITOR-2
This schematic is the motion discriminator alarm and battery monitor sections of the field monitor that is discussed in more detail a Electric Field Disturbance Monitor. (link is off-site)
- Freezing Temperature Alarm
This circuit turns on a beeper whenever the outside air temperature is less than zero degrees Centigrade. The circuit draws only a few micro amps from a 9 volt battery. It uses a glass bead thermostat accurate to 1 degree C. (added 12/04) - Freezer Over-Temperature Alarm
This circuit turns on a beeper whenever the inside temperature of a freezer is greater then zero degrees Centigrade. The circuit draws only a few micro amps from a 9 volt battery. It uses a glass bead thermostat accurate to 1 degree C. (added 12/04) . - Thermocouple Temperature Activates Relay
Voltage from a high temperature thermocouple activates a relay when the sensor detects a temperature above 1000 degrees F. - TEMPERATURE SENSOR WITH 4 TO 20mA CURRENT LOOP
I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room. The circuit uses the very robust current loop method. It uses a highly accurate semiconductor temperature sensor and an equally accurate voltage reference. The circuit includes a diode bridge, so it is polarity independent. By using the component values indicated, the circuit should not require calibration. It has a range from –40F to +120F and an accuracy of plus or minus one degree F.
· Electrode less Water Level Monitor
This system operates much like a classic float switch but without any moving parts. The illustration shows how a system using two copper coils sealed inside a plastic pipe, can detect the level of water outside the pipe. Whenever the water level is lower than the upper coil, no signal is coupled between the coils. Once calibrated, this technique might also work on the outside of a plastic water tank. (added 7/06)
· WATER SEEPAGE ALARM
This simple circuit sounds a beeper when its electrodes detect water. A single 1.5v N cell powers it. A small 1.5v button battery will also work.
- 200MHz400MHz VOLTAGE controlled OSCILLATOR
If you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine. It uses four voltage-controlled capacitors to change the frequency. - 300V PEAK TO PEAK SIGNAL GENERATOR
This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times. - AUDIO FREQUENCY DIGITAL NOISE GENERATOR
When you need to test an audio circuit with broadband noise, this circuit works great. It uses just three inexpensive C-MOS ICs that generate a series of output pulses whose widths vary randomly. I included a level control pot. - 12V TOUCH SWITCH EXCITER CIRCUIT
This circuit is designed to generate a 20KHz pseudo sine wave signal that can power about 50 remote touch activated switch circuits. It can support a cable length of about 2500 feet. A typical remote switch circuit is also shown as well as a receiver circuit for those switches. - 40KHZ LED TEST SIGNAL GENERATOR
This 40KHz crystal controlled oscillator circuit drives an infrared LED with powerful 40ma pulses. The circuit can be used to test optical communications circuits, designed to receive 40KHz modulated light signals. - CMOS INVERTER 125KHz LC OSCILLATOR
This circuit uses a single CMOS inverter to form a series resonant LD oscillator. The values shown set the oscillation at about 125KHz but other frequencies are possible by changing the main LC values. - CMOS INVERTERS FORM 125KHZ OSCILLATOR
This circuit is similar to schematic CMOS INVERTER 125KHz LC OSCILLATOR but inverts the LC components so the inductor is grounded. Two inverters are needed to produce the needed oscillation. Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies. - CMOS NAND GATE FORMS GATED 125KHZ OSCILLATOR
This circuit is similar to schematic CMOS INVERTER 125KHz LC OSCILLATOR but uses a NAND gate as an inverter. The gate allows the oscillator to be gated on and off. Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies. - HIGH POWER TOUCH SWITCH EXCITER CIRCUIT
If you have hundreds of touch switches that need an excitation signal, then this circuit is what you need. Its 20KHz 20v peak to peak output signal can supply up to 3 watts of touch switch excitation power. - MEDIUM POWER 125KHZ OSCILLATOR
This circuit is similar to CMOS INVERTERS FORM 125KHZ OSCILLATOR but adds more invertors in parallel to deliver more power. The values shown are for 125KHz. - MEDIUM POWER 125KHZ OSCILLATOR-2
This circuit is similar to MEDIUM POWER 125KHZ OSCILLATOR but adds even more inverters in parallel to deliver yet more power. The values shown are for 125KHz. - SQUARE WAVE DRIVER HAS FLEXIBLE OUTPUTS
This circuit can produce an output signal ranging from DC to 100KHz. It can source a voltage ranging from 1v to 30v. It can sink a voltage ranging from zero volts to –30v. It can drive up to 200ma of current and can even be switched to a floating tristate output. - VERY LOW POWER GATED CRYSTAL OSCILLATOR
The circuit gates the output of a continuously operating 32KHz crystal oscillator to the input of a C-MOS buffer when clock pulses are needed. The technique gets around the problem of a slow starting crystal oscillator by keeping the oscillator going and switching on a transistor power stage only as needed. The method keeps the standby power consumption to a very low 1uA when used with a 3v supply. - VERY LOW POWER ASTABLE MULTIVIBRATOR
This classic circuit draws only 200 nanoamps from a 1.5v supply - ULTRA PURE 125KHz SINE WAVE SIGNAL SOURCE
For some RFID systems operating at 125KHz, a very low distortion signal source reference is needed. The circuit shown on this page produces a 10 volt peak to peak signal into a 50 ohm load, with a distortion of only 0.01%. - Broken Solar Panels
As illustrated below, one way to salvage a large number of broken solar cells is to wire them in parallel, not in the more conventional series connection. Broken cells of various sizes and shapes are grouped together into panels of about one quarter to one full square foot in area. Those panels are then wired in series with other similar panels. The result... - Dark Activated 12v Power Supply Switch
Using an inexpensive phototransistor, this circuit switches 12v to 24v power to a load, whenever the sun goes down. - Solar Insulation Monitor
An inexpensive PIN photo diode and a 1ma meter movement form a simple sunlight intensity monitor. The sensor should be placed inside a lightly frosted glass hemisphere to minimize the influence of the sun’s angle on the sensor. An adjustment resistor calibrates the meter for a full scale reading under a one sun condition. An unshielded two conductor cable links the sensor to the meter movement. The sensor and meter can be separated by up to 200 feet. - Solar Cell Test Fixture
If you are considering building your own solar panel, you might try building the solar cell tester shown below. When constructing a solar panel it is important to make sure that all the solar cells used in the panel be closely matched for their short circuit current. One weak cell will lower the efficiency of the whole panel. The system shown allows individual solar cells to be tested for their short circuit current under a constant light intensity condition.... - Solar Powered Lithium Ion Battery Charger
The circuit below feeds a controlled current and voltage to a 3.6v lithium ion battery. The current is limited to 300ma and the voltage is limited to 4.2 volts. The circuit uses a LTC1734 IC from Linear Technology. No diode is needed between the circuit and a 6 volt solar panel.... - Solar PV cell Test Fixture
This is an illustration of a test fixture, which can be used to test individual solar cells for short circuit current. Using a PIN photo diode and a control circuit, the solar cells can be tested under constant light level conditions. A halogen incandescent lamp is used as the light source. (added 7/06) - Solar Insulation Monitor
An inexpensive PIN photo diode and a 1ma meter movement form a simple sunlight intensity monitor. The sensor should be placed inside a lightly frosted glass hemisphere to minimize the influence of the sun’s angle on the sensor. An adjustment resistor calibrates the meter for a full scale reading under a one sun condition. An unshielded two conductor cable links the sensor to the meter movement. The sensor and meter can be separated by up to 200 feet.
· CHARGE COUPLED BI-DIRECTIONAL POWER MOSFET RELAY
The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line into the control circuit is a tiny 4uA. Only about 1.5mA of DC is needed to turn on and off 400 watts of AC or DC power to a load.
- Solid State Relay Requires Ultra Low Control Current
Most solid state relays require at least 5ma and often more input control current, to fully turn on the device. But such current levels often force battery powered circuits to use excessively large batteries. The relay hobby circuit shown below demands only 50uA of input current. This about 100 times lower than that needed by a typical optically isolated solid state relays. The circuit uses a combination of a high current triac and a very sensitive low current SCR, to control up to 600 watts of power to a load, while providing full isolation and transient protection.
· SOLID STATE RELAY REQUIRES ONLY 50uA DRIVE CURRENT
This circuit demands a control current that is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery powered systems. Using a combination of a high current triac and a very sensitive low current SCR, the circuit can control about 600 watts of power to load while providing full isolation and transient protection.
- Audio Activated Switch
Drawing only 2uA from a 3v lithium battery, this circuit will turn on a transistor switch, whenever it detects an audio signal greater than 0.035v RMS. - 12v Light/Dark Lamp Switch
At night, this circuit will route current to a 12v lamp, turning it on. (added 7/06) - 12v Light/Dark Switch 2 NEW
Often, for certain low voltage lighting systems; you would like to turn off the lights during the bright light of the day. Most commercial day/night switches are designed for AC lighting. The circuit below was designed for a 12v DC system. But, it could be modified for other voltage as well. It uses an inexpensive phototransistor as the light detector. An n-channel FET is used to switch power to the lights. A transistor circuit is included to provide some hysteresis. This keeps the circuit from fluttering the light during the transition from day to night and night to day. It is recommended that a plastic tube be placed over the transistor to prevent it from being illuminated by the lights it is controlling. By selecting the appropriate power FET, the circuit could control over 100 watts worth of 12v lighting. (July 22, 2008) - 120VAC Touch Switch
This is a capacitance based touch on/touch off switch, which can control power to a 200 watt 120vac load. (added 12/04) - 240VAC Touch Switch
This is another capacitance based touch on/touch off switch, which can control power to a 200 watt 240vac load. (added 12/04) - 12v Light/Dark Lamp Switch
At night, this circuit will route current to a 12v lamp, turning it on. (added 7/06) - Audio Activated Switch
This switch circuit is powered for years by a single 3v lithium cell. Its transistor switch closes whenever the circuit detects audio signals in excess of 50mv RMS. It can be used to trigger relays or activate indicator lights. (added 12/04) - Audio Signal Detector Switch
This circuit will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal. It could be used to turn on a relay, routing the signal to be it is needed. (added 7/06) - CIRCUIT PROTECTS FROM BATTERY POLARITY REVERSAL
This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity. The N-channel FET connects the electronic device to the battery only when the polarity is correct. The circuit shown was designed for a device powered from a single 1.5 volts button cell battery. However, the circuit will operate with higher voltages as well. - Dark Activated 12v Power Supply Switch
Using an inexpensive phototransistor, this circuit switches 12v to 24v power to a load, whenever the sun goes down. (added 7/06) - FINGER TOUCH ACTIVATED SWITCH
It does not get any easier if you want a solid state switch that is activated by the touch of a finger. Two small metal pins route voltage through the finger skin to a MOSFET switch. The circuit is great for situations where a membrane type mechanical switch is not desired. - Infrared Safety Switch
Using a slotted optical sensor, this circuit can be used as a replacement for a large mushroom pushbutton safety switch. - Piezoelectric Triggered Switch
Two different switch circuits are shown. One sources current and the second sinks current. Both switches are connected to a piezoelectric wafer. When the wafer is tapped, the switches are activated. (added 7/06) - Piezoelectric Vibration Sensor Activates Switch
An inexpensive piezoelectric wafer is used to detect vibration and when the vibration is sufficient a switch is activated. (added 7/06) - POP FREE MICROPHONE ON/OFF SWITCH CIRCUIT
This circuit uses a simple technique to eliminate the usual “pop” sound when an electret type microphone is switched on or off. The circuit is completely passive and will work on dynamic and electret type microphones. - Pushbutton Activated Service Request Beeper
A single press of a pushbutton switch turns on a beeper for one second but can’t be activated again for 60 seconds. (added 7/06)
· THROUGH GLASS PUSHBUTTON SWITCH
This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass. Pushing the button moves a magnet near the reed relay, closing the relay contacts.
- Reflected Infrared Light Switch
Infrared light reflected off a finger is used to activate this switch circuit. (added 7/06). - Shadow Activated Motion Detector Circuit
There are many ways one can detect nearby human or object motion. This circuit demonstrates one way. It detects motion by noting the changes in the shadow cast by the moving object. The hobby circuit below works quite well in typical indoor room lighting. I would not recommend its use in direct sunlight. Two small PIN photodiodes positioned about one inch apart form a shadow detector. With no shadow cast on the devices, both devices produce nearly identical current levels. The current is converted to a voltage with a load resistor in parallel with the photodiode.... - Fully Isolated 50/60Hz Sync Generator
This circuit will produce a single pulse at the zero voltage cross points of the power line voltage. An opto-coupler provides a very safe 5KV isolation.
· 1 LINE TELEPHONE LINE STATUS INDICATOR
This circuit is similar to the above circuit, but only monitors one phone line.
- 2 LINE TELEPHONE LINE STATUS INDICATOR
Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. The circuit is line polarity insensitive. - 2.45GHz RF Signal Detector
This passive RF indicator is made from a few simple parts. A 100uA moving coil meter is used to display the relative intensity of the RF signal. This circuit can be used with some cell phones and many cordless telephones. (added 7/06)
· 4 LINE TELEPHONE LINE STATUS INDICATOR
Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation.
- Freezing Temperature Alarm
This circuit turns on a beeper whenever the outside air temperature is less than zero degrees Centigrade. The circuit draws only a few micro amps from a 9 volt battery. It uses a glass bead thermostat accurate to 1 degree C. - Freezer Over-Temperature Alarm
This electronic hobby circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F). A 9v battery powers the hobby circuit. The average 9ua current is so low that the battery should last for many years.... - MICRO POWER OVER-TEMPERATURE ALARM
The circuit is powered for years by a single 3 volt lithium battery. It sounds an alarm when the temperature exceeds a certain point. With some minor changes the circuit could also be configured for an under temperature (freeze) alarm. The circuit uses a cheap but accurate thermostat as the temperature sensor. - 1 AMP CURRENT INJECTOR
When you need to measure resistance down to a few micro ohms, this circuit works great. It is powered from two "C" cell batteries and is designed to inject a well-regulated one amp of current into the unknown resistance. By measuring the voltage drop across the resistor with a digital voltmeter, the resistance value can be accurately measured. The circuit also is equipped with a low battery monitor. Published in Popular Electronics, November 1992 - 120vac Under Voltage Tester
Using a cheap 24vac transformer, this circuit can test a product under low 95vac conditions. With the components show, it has a rating of 250 watts max.
· Brownout Voltage Tester
I used this circuit years ago to test AC line powered devices under 95vac line voltage conditions. It has a rating of 250 watts.
- Cheap Light Power Meter
Some time ago I was experimenting with the use of some low leakage photovoltaic solar cells, to harvest some energy from the diffuse lighting inside a room. The plan was to use a small array of solar cells (the type often used on solar powered calculators) to keep a super capacitor charged, drawing power from the light within an inside room... - Cheap Electrostatic Discharge Tester
Anyone who has ever had a shocking experience on an especially dry day is acutely aware of the kinds of high voltage that can be generated from a simple walk across a carpeted floor. Those same finger to metal sparks can destroy or disrupt sensitive electronic circuits. Good design practices take great care to avoid such potential disasters by maintaining sufficient insulation between metal or plastic enclosure parts and the electronics within or by shielding any especially sensitive components.... - Electrical Current Indicator
I designed this circuit as a simple current indicator for any load ranging from 40 watts to 250 watts. The circuit turns on a small LED, whenever it detects current flowing to a remote load. - Full wave Rectifier
Using a LF412 high speed dual op amp, this circuit will rectify any signal up to about 100KHz with a minimum amplitude of about 50mv peak to peak. - Modulated Laser Diode Tester
This circuit can either be used to test laser diodes or as a general purpose modulated light source. The circuit has an adjustable diode threshold current and an adjustable modulation frequency. The frequency can be adjusted from below 30KHz to above 50MHz. It is powered from a 9v battery. - ISOLATED AC CURRENT MONITOR
This circuit uses a small AC current transformer from Magnetek to produce an isolated voltage proportional to the AC current in the primary winding. The transformer contains a single turn primary with a low 0.001 ohm resistance. It can easily handle 30 amps of AC current and provides at least 500vac of isolation. With the components shown, the output AC voltage is scaled so 1 amp of current produces 100mv of AC voltage. - RS232 Serial Interface Status Indicator
I designed this circuit many years ago and have used it several times since. It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link. The thresholds are set at plus 3 volts and minus 3 volts. Two dual color LEDs are used as indicator lights. - PRECISION FULL WAVE RECTIFIER
I have used this handy circuit many times. It accurately converts an AC signal into pulsing DC, which can be filtered to provide an average of the input voltage. It works from mill volts to volts. The circuit shown requires a stable +5v reference if a single power supply is used. - Solar Cell Test Fixture
If you are considering building your own solar panel, you might try building the solar cell tester shown below. When constructing a solar panel it is important to make sure that all the solar cells used in the panel be closely matched for their short circuit current. One weak cell will lower the efficiency of the whole panel. The system shown allows individual solar cells to be tested for their short circuit current under a constant light intensity condition - Power Loss Indicator
Dave Campbell designed this clever circuit. It uses two neon lamps to indicate if power to a 120vac appliance had been interrupted. - Solar PV cell Test Fixture
This is an illustration of a test fixture, which can be used to test individual solar cells for short circuit current. Using a PIN photo diode and a control circuit, the solar cells can be tested under constant light level conditions. A halogen incandescent lamp is used as the light source. (added 7/06) - TEMPERATURE SENSOR WITH 4 TO 20mA CURRENT LOOP
I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room. The circuit uses the very robust current loop method. It uses a highly accurate semiconductor temperature sensor and an equally accurate voltage reference. The circuit includes a diode bridge, so it is polarity independent. By using the component values indicated, the circuit should not require calibration. It has a range from –40F to +120F and an accuracy of plus or minus one degree F. - White LED Life Tester NEW
This simple circuit is designed to plug into a standard AC electrical outlet. It uses four super bright white light emitting diodes (LED) in conjunction with a capacitor coupled full wave rectifier circuit. The LEDs are mounted in a box and are angled slightly to bounce the light off of a nearby wall. The light should last about 10 years. The circuit draws less than one half of one watt of power and can therefore run continuously. In spite of the low power, the LEDs provide sufficient illumination for most night light applications. Circuit component values for both 120vac and 240vac are shown.
· CIRCUIT FORMS DIVIDE BY 1.5 COUNTER
Two inexpensive ICs divide a TTL clock signal by 1.5. By following the circuit with another flip/flop, you could also generate a divide by three function.
· SOLID STATE RELAY REQUIRES ONLY 50uA DRIVE CURRENT
This circuit demands a control current that is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery-powered systems. Using a combination of a high current TRIAC and a very sensitive low current SCR, the circuit can control about 600 watts of power to load while providing full isolation and transient protection.
- Laser Used as Vehicular Traffic Counter
This is an illustration how a laser could be used to count traffic and measure the speed of each car passing through the sensor area. (added 7/06) - HO Train Model Lighthouse Flasher
HO train sets often have authentic looking scale model homes and buildings. The hobby circuit below can be mounted inside a model lighthouse. The electronic circuit drives a single LED lamp in such a way that it produces light which simulates the rotating light from a lighthouse beacon. It uses a dual low power op amp IC. - 300V PEAK TO PEAK SIGNAL GENERATOR
This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times. - CHARGE COUPLED BI-DIRECTIONAL POWER MOSFET RELAY
The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line into the control circuit is a tiny 4uA. Only about 1.5mA of DC is needed to turn on and off 400 watts of AC or DC power to a load.
· CHARGE PUMP EFFICIENTLY DIVIDES SUPPLY VOLTAGE
This circuit uses a few FETs and logic devices to down convert a DC voltage to about one half its value.
- CIRCUIT PROTECTS FROM BATTERY POLARITY REVERSAL
This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity. The N-channel FET connects the electronic device to the battery only when the polarity is correct. The circuit shown was designed for a device powered from a single 1.5 volts button cell battery. However, the circuit will operate with higher voltages as well. - FET INPUT HIGH SPEED LIGHT DETECTOR
This circuit is yet another design that converts current from a PIN photo diode to a voltage. It has a bandwidth that extends beyond 50MHz.
· NPN/PNP TRANSISTOR TESTER
I designed this circuit about 30 years ago and still use it from time to time. It is powered from a 3v battery. It makes a tone when the transistor tests good. It can be used to determine device type (NPN or PNP) and the base, collector or emitter transistor pins. It can also test most transistors will still connected to a circuit.
- VERY LOW POWER ASTABLE MULTIVIBRATOR
This classic circuit draws only 200 nanoamps from a 1.5v supply. - 175KHz Inductive Pulse Transmitter
This circuit is discussed in more detail in the Experimenters Journal. The transmitter’s six inch diameter coil launches powerful magnetic 175KHz ring pulses that can be detected by the circuit below.
· Plastic Pipe Finder
I used this circuit once to track down the location of a plastic pipe, buried underground. It transmits a weak RF signal, which can be picked up by a portable AM radio from about 6 feet away.
- Freezing Temperature Alarm
This circuit turns on a beeper whenever the outside air temperature is less than zero degrees Centigrade. The circuit draws only a few micro amps from a 9 volt battery. It uses a glass bead thermostat accurate to 1 degree C. - Freezer Over-Temperature Alarm
This electronic hobby circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F). A 9v battery powers the hobby circuit. The average 9ua current is so low that the battery should last for many years.... - Thermocouple Temperature Activates Relay
Voltage from a high temperature thermocouple activates a relay when the sensor detects a temperature above 1000 degrees F. (added 7/06) - 40KHz TV-VCR LIGHT SOURCE REPEATER
This circuit is designed to be placed directly in front of a standard TV or VCR remote. The exiting light pulses produced by the circuit match the pulses from the remote but are about 10 times more powerful. Using the device, the remote can operate a TV or VCR over three times the normal distance.
- 40KHz Ultrasound Receiver
A X100 transistor amplifier is followed by a zero cross detector circuit, using a voltage comparator. The output is a TTL logic signal, corresponding to the received 40KHz signal. (added 7/06) - Medium Power 40KHz Ultrasound Transducer Driver
This crystal controlled circuit drives a 40KHz piezoelectric transducer with a 30v peak to peak signal. (added 7/06)
- 40KHz Ultrasound Receiver
A X100 transistor amplifier is followed by a zero cross detector circuit, using a voltage comparator. The output is a TTL logic signal, corresponding to the received 40KHz signal. (added 7/06) . - PRECISION ULTRA LOWER POWER OSCILLATOR
This circuit works much like the classic 555 timer, but draws only about 1.5 micro amps from a 3 volt battery. It is highly stable under varying temperature and supply voltages. - Wide Band Zero Cross Detector
This circuit was designed to convert a low amplitude 40KHz signal into a clean square wave signal. It will work with inputs as small as 5mv peak-to-peak or as large as 3 volts peak to peak. The input frequency can range from a few kilohertz to about 150KHz. - 240VAC TO 5VDC Power Supply
This is simple way to power some 5v logic from a 240vac source. If a 120vac power adapter is used, the circuit will also work for 120vac power lines.
- Watt-Hour Meter Monitor: This is a simple and safe way to monitor the power and energy use of a typical home. A battery powered device is attached to the top of a typical spinning wheel type watt-hour meter. The device contains a visible red LED and a PIN photo diode. Light pulses are bounced off of the watt-hour meter’s spinning wheel. The circuit detects the black mark on the wheel and produces a clean TTL level logic signal, equal to the frequency of the wheel spin. This information can be connected to a low power RF transmitter to send to a matching receiver, where the information can be recorded and displayed.
- MICROPOWER PULSE GENERATOR
it is hard to design a pulse generator that produces clean logic pulses while drawing very low current. This circuit is designed to produce short 2mS pulses at a rate of one per second while drawing only 1 micro amp from a 9 volt battery. - VIDEO SIGNAL EDGE ENHANCEMENTS
I designed this circuit many years ago, based on the claims that the technique would improve the quality of standard TV images. The circuit adds information to the edges of the objects and was reported to bring out more detail. After building and testing the circuit, I could definitely see a difference between it and a regular TV display but I don’t think most people would go to the trouble of installing the circuit for only a marginal improvement. Still, it is an interesting circuit with which someone might experiment.
· ULTRA PURE 125KHz SINE WAVE SIGNAL SOURCE
For some RFID systems operating at 125KHz, a very low distortion signal source reference is needed. The circuit shown on this page produces a 10-volt peak-to-peak signal into a 50-ohm load, with a distortion of only 0.01%.
- Ramping LED Driver
The circuit below was designed to drive a LED with an intensity ramping mode. Two 555 timers generate two different triangle waveforms. The upper device generates a 10KHz signal while the lower unit produces a 1Hz signal. The two signals are fed to a voltage comparator. The result is a pulse width modulation (PWM) signal, which with the aid of the FET, drives the LED in such a way that its average light output slowly ramps from about zero light to maximum and then slowly dims back down. The circuit should operate over a supply voltage ranging from 3v to 12v. You can easily vary the ramping time by changing the value of the 1M resistor. For an interesting effect, you can place a 1N4148 diode in parallel with the 1M resistor, with the cathode (banded end) side connected to pin 3. - White LED Life Tester NEW
This simple circuit is designed to plug into a standard AC electrical outlet. It uses four super bright white light emitting diodes (LED) in conjunction with a capacitor coupled full wave rectifier circuit. The LEDs are mounted in a box and are angled slightly to bounce the light off of a nearby wall. The light should last about 10 years. The circuit draws less than one half of one watt of power and can therefore run continuously. In spite of the low power, the LEDs provide sufficient illumination for most night light applications. Circuit component values for both 120vac and 240vac are shown. - WHITE LED NIGHT LIGHT
This simple circuit is designed to plug into a standard AC electrical outlet. It uses four super bright white light emitting diodes (LED) in conjunction with a capacitor coupled full wave rectifier circuit. The LEDs are mounted in a box and are angled slightly to bounce the light off of a nearby wall. The light should last about 10 years. The circuit draws less than one half of one watt of power and can therefore run continuously. In spite of the low power, the LEDs provide sufficient illumination for most night light applications. Circuit component values for both 120vac and 240vac are shown.
- 2.45GHz RF Signal Detector
This passive RF indicator is made from a few simple parts. A 100uA moving coil meter is used to display the relative intensity of the RF signal. This circuit can be used with some cell phones and many cordless telephones. (added 7/06) - 9v POWERED XENON PHOTOFLASH Controller
This 9v battery powered circuit is designed for remote control flash needs. A charge control circuit turns off the high voltage generator when the photoflash capacitor is fully charged. A neon lamp is included to indicate when the system is ready to flash. - AIR TRANSPARENCY MONITOR, XENON FLASH TRANSMITTER
This is the matching transmitter for the above receiver. The transmitter launches powerful 1000-watt light pulses that last about 20 microseconds. - LINE POWERED XENON FLASH TRANSMITTER
This line powered xenon flash circuit drives a small camera type flash tube. It has an optical isolator to allow the flash to be safely triggered from some remote device. A flash rate of 2Hz is possible with the circuit. - XENON LAMP FLASH DETECTOR
This circuit uses a small 2.5mm square photo diode in conjunction with a 100mH coil to detect the short light flashes from a xenon lamp. The coil makes the circuit immune to normal room lights. Its 10mv sensitivity can detect light flashes from a range of over 100 feet. Reflections from a room’s walls and ceiling is usually enough to trigger the circuit. The entire circuit draws only 3 Micro amps from a 6 to 9 volt battery.
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