Resistance-ratio detector
Applications such as photoelectric control, temperature detection and moisture sensing require a circuit that can accurately detect a given resistance ratio. A ...
Magnetometer
The circuit uses two general-purpose npn transistors, Ql and Q2, and a special hand-wound, dual-coil probe ferrets out the magnetism. Ql and its associated comp...
Linear transformer signal conditioner
A1 and its associated components furnish an amplitude stable sine wave source. All positive feedback path is a Wein bridge, tuned for 1.5 kHz, Ql, the LT1004 re...
Photodiode signal conditioner
The photodiode specified responds linearly to light intensity over a 100 dB range. Digitizing the diodes linearly amplified output would require an A-D converte...
Monostable photocell circuit
A photocell circuit provides automatic threshold adjustment. Monostable action prevents undesired retriggering of the output. With only one op amp IC, the circu...
Modulated light-beam circuit
Feedback control of the phototransistor in this optical detector helps negate the effects of varying ambient light sources. The output of a modulated visible-li...
Robot eyes
An infrared LED and a phototransistor are used for each eye. Half of a 556 timer IC (ICl-a) functions as an as table multivibrator oscillating at a frequency of...
Light-seeking robot
The circuit is light seeking; it will follow a flashlight around a darkened room. A pair of photocells determine the direction in which the robot will move. Eac...
Twilight switch circuit
As dusk begins to -fall, the sensor (a cadmium-sulfide light-dependent resistor or LDR) operates a small horn to provide an audible reminder that it's time to t...
LED operates as light sensor
Using a simple 741 amplifier connected as a current-to-voltage converter with the LED as the current source, the voltage at the output is proportional to incide...
Photoelectric switch
The CDS cell resistance decreases in the presence of light, turning on the 2N3904 relay driver.
...
Light-operated switch
This circuit uses a flip-flop arrangement of Ql and Q2. Normally Ql is conducting heavily. Light on CDS photocell causes Ql bias to decrease, cutting it off, tu...
Laser light detector
The laser light detector utilizes a sensitive photo transistor (Q5) placed at the focal point of a lens (LE2). The output of Q5 is fed to a sensitive amplifier ...
humidity sensor circuit II
When the 14B-12B pair opens, 12B is connected to Al's summing point via 13B. The sensor now discharges into the summing point through the 1 µ capacitor. Sinc...
humidity sensor circuit
This circuit combines two LTC1043s with a based humidity transducer in a simple charge-pump based circuit. The sensor specified has a nominal 400 pF capacitance...
Angle of rotation detector
The figure shows two TL3103 linear Hall-effect devices used for detecting the angle of rotation. The TL3103s are centered in the gap of a U-shaped permanent mag...
Gas analyzer circuit
The circuit shows a simple yes/no gas detector. Three 1.5-V D cells are used as a power supply, with SI acting as an on/off switch. The heater is energized dire...
Toxic gas detector
The major device in the circuit is SRI (a TGS812 toxic-gas sensor manufactured by Figaro Engineering Inc.) The gas-sensitive semiconductor (acting like a variab...
Gas and vapor detector
The power drain is approximately 150 mA. IC1 provides a regulated 5-volt supply for the filament heater of the sensor. The gas sensitive element is connected as...
Lie detector
The two probes shown are held in the hands and the skin resistance applies bias to the transistor. The 5 k ohm pot is set for zero deflection on the meter. When...