Proximity-sensor
The SillOO series circuit input is connected to a capacitive field sensor-possibly a piece of doublesided circuit board. Any induced voltage change on the plat...
Proximity-switch
A 3-x -3-inch piece of circuit board, or similar size metal object which functions as the pick-up sensor, is connected to the gate of Ql. A 100-MD resistor, ...
Ph-probe-and-detector
The greatest sensitivity is achieved if R1 is approximately equal to the probe resistance. The circuit can be zeroed with R2, while the full-scale voltage is c...
Flash-meter
Insulated-gate, field-effect transistor (IGFET), Q2 and silicon photo cell Zl form the heart of this circuit. Transformer T1 is an audio-output type, but it"s ...
Photodiode-source-follower
A common method of transforming the output current of a photodiode into a voltage signal, paralleling the photodiode with a high-value load resistor, produces ...
Ambient-light-ignoring-sensor
A resonance-tuned narrow-band amplifier reduces this optical object detector"s sensitivity to stray light. C1 and L1 in IC2A"s feedback loop cause tbe op amp t...
Automatic-fan-speed-controller
The controller circuit can reduce a fan"s noise, power consumption, and wear, particularly in the presence of a low, fluctuating ambient temperature. Mount a t...
Air-motion-detector
When a current of air hits tbe piezo element, a small signal is generated and is fed through Cl and Rl to inverting input pin 2 of one section of the LM324. Th...
Bar-code-scanner
The circuit illustrates a method of interfacing a HEDS-1000 emitter-detector pair with a HA-5144 for use as a bar-code scanner circuit. The HA-5144 is used as ...
Acid-rain-monitor
A simple bridge rectifier and a 12-V regUlator powers the MOSFET sensing circuit. The unregUlated output of the bridge rectifier operates the drain solenoid vi...
Breath-alert-alcohol-tester
When power is applied to the circuit, the heater coil in the sensor is energized by the 5-V output of IC5, a 7805 voltage regulator. Breathing into the sensor ...
Closed-loop-tracer
The tracer, consisting of both a transmitter and receiver, is designed to follow a closed-loop wire or cable system. It follows an induced voltage path creat...
Constant-current-stimulator
Most circuits that provide an electrical stimulus for research subjects are constant-voltage designs; this circuit is a constant-current design. Stimulator cir...
Breath-monitor
The mercury-in-rubber strain gauge is the detector of breathing. In the model device, the strain gauge produced by Medimatic, Demark was used. The change in th...
Simple-continuity-tester
The pitch of the tone is dependent upon the resistance under test. The tester will respond to resistances of hundreds of kilohms, yet it is possible to disti...
Low-power-magnetic-current-sensor
A transducer senses a direct current magnetically, providing isolation between the input and the output. The detecting-and-isolating element is a saturable rea...
Stud-finder
The CS209 is designed to detect the presence or proximity ofmagnetic metals. It has an internal oscillator that, along with its external lc resonant circuit, pr...
Paper-sheet-discriminator
The circuit outputs power to the drive motor when one or no sheets are being fed, but interrupts motor power when two or more superimposed sheets pass through ...
Electrostatic-detector
The heart of the electroscope is the two junction FETs Ql and Q2 connected in a balanced-bridge circuit. The gate input of Ql is connected to the wire pick-up ...
Lvdt-driver-demodulator
A very simple motion transducer can be constructed using the circuit shown. The output is biased to one-half the supply voltage. This requires special interfac...