Tone-actuated relay
The circuit is built around the LM567 tone decoder IC that requires about 100 millivolts at its operating frequency. The frequency is set by a 10 K variable res...
Geiger counter
The Geiger tube needs a high voltage supply which consists of Ql and its associated components. The transformer is connected in reverse; the secondary is connec...
Wideband radiation monitor
A sensitive radiation monitor may be simply constructed with a large-area photodiode and a quad operational amplifier. Replacing the glass window of the diode w...
Automatic plant waterer
The unit consists of a sensor, timer, and electric water pump. The sensor is embedded in the soil, and when dry, the electronics operate the water pump for a pr...
Moisture detector
The detector is made of fine wires spaced about one or two inches apart. When the area between a pair of wires becomes moistened, the horn will sound...
Digital weight scale
This circuit employs a potentiometer as the weight sensing element. An object placed upon the scale displaces the potentiometer wiper, an amount proportional to...
Liquid level detector
When liquid level reaches both probes, alarm is turned on...
Water-level sensing control circuit
The circuit applies power to the load until the water conducts through the probe, and bypasses gate current from the low current SCR...
Liquid level detector
Alarm is actuated when liquid level is above the probes and remains activated even if the level drops below the probes...
Liquid level control
Use this circuit to keep the fluid level of a liquid between two fixed points. Two modes, for filling or emptying are possible by simple reversing the contact c...
Fluid level controller
This circuit can be used to maintain fluid between two levels...
Level sensor for cryogenic fluids
The sensor circuit is adaptable to different liquids and sensors. The constant-current source drives current through the sensing probe and a fixed resistor...
Linear light-meter circuit
This circuit uses a low-input-bias op amp to give a steady dc indication of light level. To reduce circuit sensitivity to light, Rl can be reduced, but should n...
Light beam operated on-off relay
When a beam of light strikes the photocell, the voltage across neon lamp NE-1 rises sharply. NE-1 turns on and fires the SCR. Kl is an impulse relay whose conta...
Precision photodiode level detector
The output state changes at a photo diode current of 0 µA...
Optical receiver
The MFODllOO PIN diode requires shielding...
Light interruption detector
When the light incident on the LASCR is interrupted, the voltage at the anode to the 2N4990 unilateral switch goes positive on the next positive cycle of the po...
Adjustable light detection switch
R2 sets the circuit"s threshold. When the light intensity at PCI"s surface is decreased, the resistance of PCI a cadmium-sulfide photo-resistor is increased. Th...
Optical schmitt trigger
This circuit shows a 555 with its trigger and threshold inputs connected together used to energize a relay when the light level on a photoconductive cell falls ...
Precision photodiode comparator
Rl sets the comparison level. At comparison, the photodiode has less than 5 mV across it, decreasing dark current by an order of magnitude...