TTL type Q and inverted Q inputs control a classic H-bridge circuit, rated at 50 volts and about 10 amps. The circuit can control power and direction of a DC motor. (added 7/06)
- 10MHz TO 20MHz LASER LIGHT DETECTOR
This circuit was originally designed to detect laser light pulses for an optical Ethernet communications system. It has good ambient light immunity. - 20MHz VCSEL 3mW LASER TEST CIRCUIT
This circuit takes advantage of some new vertical cavity surface emitting lasers (VCSEL) that don’t require light output control circuits. The circuit shows how to drive the device from a single high speed CMOS IC. The circuit can easily be modified to transmit signals from kilohertz to about 50MHz. - BROAD BAND 2MHz OPTICAL FIBER RECEIVER
If you need more sensitivity than the above circuit this circuit provides about ten times more gain. It too is designed around an inexpensive plastic optical fiber detector. - BROAD BAND 5MHz OPTICAL FIBER RECEIVER
This circuit is a simple broad band light detector that uses a very inexpensive IC and a PIN photodiode that is packaged for use with plastic optical fibers. It has a bandwidth from 1KHz to over 5MHz. It is great for experimenting with various modulated light sources.
CMOS Logic Inverter Amplifier Characteristics
This chart shows some of the measured characteristics of three different unbuffered CMOS logic gates, used as voltage amplifiers.
- C-MOS INVERTER MAKES LOW POWER AMP
With the addition of one resistor and a capacitor, some common logic ICs can be transformed from digital to analog duties. This circuit outlines some the features to expect from different inverter ICs. - 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. - N-CH AND P-CH TRANSISTORS FORM PUSH-PULL DRIVER
This circuit can produce high speed output signals with fast rise and full times. The unique change pump action allows the voltage of the upper P-ch device to range from mill volts to hundreds of volts. The output current is only limited by the rating of the transistors. I have used this circuit beyond 2MHz.
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.
- CMOS Logic Inverter Amplifier Characteristics
This chart shows some of the measured characteristics of three different unbuffered CMOS logic gates, used as voltage amplifiers. - ELECTRIC FIELD DISTURBANCE MONITOR
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. - HIGH PASS ACTIVE FILTER COLLECTION
This is a collection of inverting and non-inverting active high pass filter circuits. I included one, two three, four and six pole filter circuits. You can change the component value ratios shown to achieve any frequency cut-off you may need. The circuit does not specify an operational amplifier. The circuits should be used to select the needed resistor and capacitor components for a particular frequency knee and slope. - 10MHz TO 20MHz LASER LIGHT DETECTOR
This circuit was originally designed to detect laser light pulses for an optical Ethernet communications system. It has good ambient light immunity. - 20MHz VCSEL 3mW LASER TEST CIRCUIT
This circuit takes advantage of some new vertical cavity surface emitting lasers (VCSEL) that don’t require light output control circuits. The circuit shows how to drive the device from a single high speed CMOS IC. The circuit can easily be modified to transmit signals from kilohertz to about 50MHz. - BROAD BAND 2MHz OPTICAL FIBER RECEIVER
If you need more sensitivity than the above circuit this circuit provides about ten times more gain. It too is designed around an inexpensive plastic optical fiber detector. - BROAD BAND 5MHz OPTICAL FIBER RECEIVER
This circuit is a simple broad band light detector that uses a very inexpensive IC and a PIN photodiode that is packaged for use with plastic optical fibers. It has a bandwidth from 1KHz to over 5MHz. It is great for experimenting with various modulated light sources.
CMOS Logic Inverter Amplifier Characteristics
This chart shows some of the measured characteristics of three different unbuffered CMOS logic gates, used as voltage amplifiers.
- C-MOS INVERTER MAKES LOW POWER AMP
With the addition of one resistor and a capacitor, some common logic ICs can be transformed from digital to analog duties. This circuit outlines some the features to expect from different inverter ICs. - 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. - N-CH AND P-CH TRANSISTORS FORM PUSH-PULL DRIVER
This circuit can produce high speed output signals with fast rise and full times. The unique change pump action allows the voltage of the upper P-ch device to range from mill volts to hundreds of volts. The output current is only limited by the rating of the transistors. I have used this circuit beyond 2MHz.
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.
- 12KV High Voltage Generator The hobby circuit below uses an unusual method to generate about 12,000 volts with about 5uA of current. Two SCRs form two pulse generator circuits. The two SCRs discharge a 0.047uF a 400v capacitor through a xenon lamp trigger coil at 120 times a second. The high voltage pulses produced at the secondary of the trigger coil are rectified using two 6KV damper diodes. The voltage doubler circuit at the secondary of the trigger coil charges up two high voltage disc capacitors up to about 12KV. Although this circuit can’t produce a lot of current be very careful with it. A 12KV spark can jump about 0.75 of an inch so the electronic circuit needs to be carefully wired with lots of space between components.
- 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. - SIMPLE NITROGEN SPARK GENERATOR
Nitrogen or air sparks are very powerful light sources that produce flashes that last only a few nanoseconds. This line powered circuit generates a continuous series of very small sparks across electrodes with a 0.05 inch gap. - MACHINE VIBRATION TRIGGERS HOUR METER
This circuit allows an off-the-shelf battery powered digital hour meter to be turned on and off, according to a machine's operation, without requiring a direct electrical connection to the machine. Machine vibrations are detected by an off-the-shelf piezoelectric wafer. The wafer is normally used as a sound generator. The 3v power could be tapped from the hour meter's own lithium battery or from a separate 3v lithium battery. The circuit only draws about 1.5uA, so a 250mA-hr battery would power the circuit for about 10 years. Published in EDN, Jan 16, 1997
ELECTRIC FIELD DISTURBANCE MONITOR
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. (this link is off-site) 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. (this link is off-site)
- 1 LINE TELEPHONE LINE STATUS INDICATOR
This circuit is similar to the above circuit, but only monitors one phone line. - 1.5V LED FLASHER VERSION A
Many published circuits that flash LEDs need 3 volts or more. This circuit uses only a single inexpensive C-MOS IC and flashes the LED for a full year on a single 1.5-volt AA alkaline battery cell. The circuit uses a charge pump technique to provide the LED the needed voltage. - 1.5V LED FLASHER VERSION B
To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency. A small 1.5-volt alkaline N cell should flash the LED for a full year. It too uses a "charge pump" technique to provide a LED the needed voltage. - 120vac/240vac Indicator
Two LEDs indicate if a power line has 120vac or 240vac voltage on it. - 125KHz Wireless Smart Key Detector
This circuit will turn on an indicator light whenever it detects a smart car key containing an RFID chip. - 12v Lamp Current Indicator
This circuit turns on a LED indictor light whenever DC current flows into a 12v lamp. - 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. - 3v Low Battery Voltage Flasher
Many battery powered devices use two AA alkaline cells. Often you will not know when it is time to replace the batteries until the device powered by them actually stops operating. The hobby circuit below can be connected to a 3v battery, to give you some warning when the battery is nearing its end of life. It will flash a LED when the battery voltage drops to about 2.4 volts. The electronic circuit draws only 1ua of current in standby mode and jumps to only 20ua when flashing, so it can safely... - 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. - AC Current Indicator Light
This circuit could be wired into a 120vac power line, which feeds power to any load, ranging from 40 watts to 250 watts. It will turn on a LED light whenever current is being drawn by a load. It is especially useful for remote lights, where you may not be able to see if the lamps are receiving power. - ACCEPTABLE VOLTAGE INDICTOR
I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed. The circuit can also be used to adjust a particular voltage be within specific high or low limits. The three LEDs will indicate if the voltage is high, low or OK. When connected to other converters, such as a frequency to voltage converter, a current to voltage converter or a power to voltage meter, it could provide a quick indication of a proper level. - Automotive Electrical Voltage Indicator
This circuit will indicate if an automotive electrical circuit has zero volts or 12 volts present. (added 7/06) - Battery Charge Current Indicator
This circuit turns on a LED whenever it detects at least 25ma of battery charge current. (added 7/06) - 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. - FLASHING LED POWER INDICATOR DRAWS LOW CURRENT
This circuit flashes a power indicator LED to keep the average current low. - High DC Current Indicator
A while back, someone requested a simple method to indicate when 20 to 50 amps of DC current was flowing through a wire. The circuit below works well and is about as simple as you can get. A sensitive reed relay from www.Jameco.com acts as the current sensor. The magnetic field produced by such a current is enough to close the relay contacts, if one or two turns are wound around the relay. The turns do not have to be tight. I was able to close the contacts with two turns about 2 inches in diameter with 20 amps. A simple LED and resistor can be used to indicate the current by tapping into the automotive +12v supply. - Moving Air Indicator
Many months ago a Discover Circuits reader wanted a method to indicate when a fan was blowing air. He didn’t want to route any electrical wires to a sensor near the fan. Instead he wanted all the electronics for both the fan and other circuits mounted some distance away from the fan. I scratched my head a bit.... - RS232 Data Bus Status Indicator
This circuit indicates TXD and RXD activity. The thresholds are set at plus 3 volts and minus 3 volts. - 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. - Remote LED Indicator Light -- NEW
There are times when you would like to transmit a signal from one LED indicator light to second LED at another location. The circuit below works well for this application. It takes advantage of the fact that the internal infrared LED inside an opto-isolator has a lower voltage drop than the visible LED being tapped into. Using a Darlington type opto-isolator also means very little current needs to be diverted to the isolator..... - 20MHz VCSEL 3mW LASER TEST CIRCUIT
This circuit takes advantage of some new vertical cavity surface emitting lasers (VCSEL) that don’t require light output control circuits. The circuit shows how to drive the device from a single high speed CMOS IC. The circuit can easily be modified to transmit signals from kilohertz to about 50MHz. - 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 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. - COLOR FILM MAKES OPTICAL FILTER
This isn’t an electronic circuit but the file shows the curve for an optical filter made from exposed color film. The material blocks most visible light but is very transparent to 880nM infrared light. Kodak 100ASA is exposed to "cool white" fluorescent light for about 5 seconds. Then, the film is developed in the usual way. The color negatives form the filter material and does a fine job of blocking visible light wavelength and passing the longer near infrared wavelengths. Published in Electronic Design, Dec 2, 1996. - Infrared Remote Extender
This electronic hobby circuit is designed to be placed directly in front of a standard TV or VCR remote. The exiting light pulses produced by the electronic 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.... - MICRO POWER 40KHz BURST LASER DIODE DRIVER
Some laser tag or simulated combat games can use this circuit to send short bursts of modulated laser light at the opponent's vest, equipped with a matching light receiver. The circuit operates from three 1.5v cells (4.5v) that should provide enough energy for about 200,000 shots. - OPTICAL RFID TEST CIRCUIT
I designed this test the concept of using light techniques to send identification data instead of RF. A more detailed discussion on this scheme can be found in the Imagineered new products section. - Pigeon Scarecrow
I have an area on my roof where a large flock of pigeons like to roost. Their nesting materials and droppings really make a mess. Often there is enough junk from them that it clogs my roof gutters. Perhaps one way to scare them away is with a device mounted on the roof near their favorite roosting spot. The device.... - Reflected Infrared Light Switch
Infrared light reflected off a finger is used to activate this switch circuit. Drawing only 30uA from a 3v supply, this circuit will detect a human finger with a range of about 1 inch. The sensor uses an inexpensive infrared LED and a matching photo diode. (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.... - Short Range Reflective Object Sensor
Drawing only 30uA from a 3v supply, this circuit will detect a human finger with a range of about 1 inch. The sensor uses an inexpensive infrared LED and a matching photo diode. - TV/VCR Infrared Remote Booster
This circuit will boost the signal from any infrared TV or VCR remote, extending the range by a factor of 3X. - VOLTAGE TO FREQUENCY CONVERTER + 1uS LED PULSE DRIVER
This circuit receives the signal from the above amplifier and launches powerful 1uS infrared light pulses from a low cost LED that are frequency modulated by the audio information. The 10KHz center frequency of the pulse stream is low enough so a standard infrared LED can emit ten times more light than conventional long pulse techniques. The circuit is described in more detail in the transmitter section of my Handbook of Optical Through the Air Communications. - 18v AC to DC Power Supply
This is a classic linear power supply which produces a regulated 18v, rated at about 1 amp. (added 7/06) - 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. - CAPS PROVIDE VOLTAGE BOOST TO SERIES REGULATOR
This circuit adds some capacitors and diodes to a traditional transformer type series regulator circuit to extend the normal operating range. It can insure regulation during low line voltage conditions or it can squeeze a few more watts out of a plug-in-the-wall power adapter power supply. - Classic Plus and Minus DC Power Supply
This is a classic example of a regulated DC power supply that produces both a positive 15v and a negative 15v from a 20vac wall adapter. (added 12/04) - 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 - Non-isolated Off-line AC to DC Power Supply
This compact efficient circuit can provide up to 100ma of a regulated 5 volts from an AC power source ranging from 20vac to 120vac.
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