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Four quadrant photo-conductive detector amplifier – Circuit Schematic
Four quadrant photo-conductive detector amplifier
Use this circuit to sense four quadrant motion of a light source...
Pulse generation by interrupting a light beam – Circuit Schematic
Pulse generation by interrupting a light beam
This circuit puts out a pulse when an object on the conveyor belt blocks the light source. The light source keeps the phototran-sistor turned on. This produces ...
Proximity detector – Circuit Schematic
Proximity detector
This circuit provides a means of detecting the presence of anything by the reflection of infra-red light and provides a direct digital output of object detectio...
Gas and smoke detector – Circuit Schematic
Gas and smoke detector
This circuit can detect smoke and a number of gases (CO, CO2, methane, coal gas and others) with a 10 ppm sensitivity. It uses a heated surface semiconductor se...
Tone detector – Circuit Schematic
Tone detector
The detector circuit is made up a two-amplifier multiple feedback bandpass filter followed by an ac-to-dc detector section and a Schmitt Trigger. The bandpass f...
Air-motion detector – Circuit Schematic
Air-motion detector
Sensing circuit detects either steady or fluctuating air flows. The heart of the circuit is a Radio Shack piezo buzzer (P/N 273-060) and an LM324 quad op amp. (...
Nanoampere sensing circuit – Circuit Schematic
Nanoampere sensing circuit
The circuit may be used as a sensitive current detector or as a voltage detector having high input impedance. Rl is set so that the voltage at point (A) is V2 t...
Micropower double ended limit detector – Circuit Schematic
Micropower double ended limit detector
The detector uses three sections of an L144 and a DC4011 type CMOS NAND gate to make a very low power voltage monitor. If the input voltage, Vin, is above Vhigh...
Undervoltage-overvoltage indicator – Circuit Schematic
Undervoltage-overvoltage indicator
This circuit will make the appropriate or above the value determined by zener diodes LED...
Proximity detector – Circuit Schematic
Proximity detector
The proximity sensor works on the principle of transmitting a beam of modulated infra-red light from the emitter diode LED2, and receiving reflections from obje...
Touch switch or proximity detector – Circuit Schematic
Touch switch or proximity detector
This circuit is actuated by an increase in capacitance between a sensing electrode and the ground side of the line. The sensitivity can be adjusted to switch wh...
Capacitance relay – Circuit Schematic
Capacitance relay
Capacitor Cl and body capacitance (C2>of the operator form the voltage divider from the hot side of the ac line to ground. The voltage across Cl is determined b...
Windshield washer fluid watcher – Circuit Schematic
Windshield washer fluid watcher
This circuit relies upon the minute current between two conductive probes suspended in a washer fluid reservoir...
Differential capacitance measurement – Circuit Schematic
Differential capacitance measurement
A bubble vial with external aluminum-foil electrodes is the sensing element for a simple indicating tiltmeter. To measure bubble displacement, a bridge circuit ...
Tilt-meter – Circuit Schematic
Tilt-meter
Electrodes are immersed in an electrolyte that remains level while the sensor follows the tilt of the body on which it is placed, more of one outer electrode an...
Differential thermometer – Circuit Schematic
Differential thermometer
The 50 k ohm pot trims offsets in the devices whether internal or external, so it can be used to set the size of the difference interval. This also makes it use...
Electronic thermometer – Circuit Schematic
Electronic thermometer
An inexpensive electronic thermometer is capable of measuring temperatures over a range of from -30°F to +120°F. A diode-connected 2N3904 transistor used ...
Remote thermometer – Circuit Schematic
Remote thermometer
The low output impedance of a closed loop op amp gives ideal line-noise immunity, while the op amp's offset voltage drift provides a temperature sensor. Using t...
Temperature-to-frequency converter – Circuit Schematic
Temperature-to-frequency converter
Al's positive input is biased by the thermocouple. Al's output drives a crude V — F converter, comprised of the 74C04 inverters and associated components...
Hi-lo temperature sensor – Circuit Schematic
Hi-lo temperature sensor
Resistors Rl, R2, and the two 2.2 k resistors form a bridge circuit. R2 is a thermistor, and Rl sets the temperature at which L2 lights....