Advertisement
Moisture Detector Circuit – Circuit Schematic
Moisture Detector Circuit
The moisture detector uses two transistors and a piezoelectric transducer to sound an alarm tone when water is present. Transistor Ql forms a crystal-controlle...
Acid-Rain Monitor Circuit – Circuit Schematic
Acid-Rain Monitor Circuit
The drain-to-source resistance of Ql varies depending on the acidity of the sample presented to Ql`s gate circuit. That variable resistance varies the current ...
Room Monitor Circuit – Circuit Schematic
Room Monitor Circuit
The circuit uses Ql to buffer the right-channel balance output while Q2 and Q3 form a VOX circuit. When the signal level from the microphone goes high, the out...
Heartbeat Monitor Circuit – Circuit Schematic
Heartbeat Monitor Circuit
An IR photodiode, which senses IR skin reflectivity as a result of increased blood volume during the periods that the heart forcibly contracts, is used to pick...
Soil Heater For Plants Circuit – Circuit Schematic
Soil Heater For Plants Circuit
A TDA1024 electronic thermostat senses soil temperature via thermistor R6. The circuit uses zero-crossing switching of the heater. The heater is made of elasti...
Simple Short Finder Circuit – Circuit Schematic
Simple Short Finder Circuit
Transistors Ql and Q2, together with resistors Rl through R7, make up the input balancing stage, which senses the resistance between points X and Y. The input ...
Light Meter Circuit – Circuit Schematic
Light Meter Circuit
The outputs from the comparators will swing, in sequence, from high to low as the input voltage rises above the reference voltage applied to each comparator. T...
Light-Controlled Oscillator Circuit – Circuit Schematic
Light-Controlled Oscillator Circuit
This circuit can be used as a light detector and possibly as an aid for the visually handicapped....
Photoelectric Sensor Circuit – Circuit Schematic
Photoelectric Sensor Circuit
The circuit can be used as a sensor that can trigger an alarm, without direct contact being made by the intruder. In this circuit, a visible or invisible light...
Combined Light-/Dark-Activated Switch Circuit – Circuit Schematic
Combined Light-/Dark-Activated Switch Circuit
Two op amps used in a bridge circuit configuration detect high and low light levels. Potentiometer R2 sets the dark level and Rl controls the light level. R3 i...
Precision Dark-Activated Switch With Hysteresis Circuit – Circuit Schematic
Precision Dark-Activated Switch With Hysteresis Circuit
A GdS cell is one leg of a bridge circuit. Potentiometer R6 iri another leg sets the trip point. Potentiometer R5 provides hysteresis adjustment to prevent cha...
Light-Dependent Sensor For Multiple Inputs Circuit – Circuit Schematic
Light-Dependent Sensor For Multiple Inputs Circuit
This light-dependent sensor uses LDRs to detect the presence or absence of light. As long as the light source striking the LDRs remains constant, the alarm doe...
Visible-Light Receiver Circuit – Circuit Schematic
Visible-Light Receiver Circuit
This receiver for amplitude-modulated light signals uses phototransistor Ql mounted in a parabolic reflector (to increase range). Any npn phototransistor shoul...
Simple Lie Detector Circuit – Circuit Schematic
Simple Lie Detector Circuit
The circuit, uses a two-transistor direct-coupled oscillator that has a frequency determined by CI, R2, and the (skin) resistance across the touch pads. Since ...
Selective Preamplifier For Infrared Photodiode Circuit – Circuit Schematic
Selective Preamplifier For Infrared Photodiode Circuit
The circuit uses a tuned circuit to achieve frequency selection. Values are for operation at about 51 kHz. ...
The Talking Compass Circuit – Circuit Schematic
The Talking Compass Circuit
A talking compass is made up using a Hall-effect direction sensor (MODI) and an ISD1016 analog audio storage device. It is possible to program eight two-second...
Geiger Counter Ii Circuit – Circuit Schematic
Geiger Counter Ii Circuit
Ql is a pnp power transistor used in conjunction with a ferrite transformer to form a blocking-type oscillator. This oscillator is a fixed- frequency type, and...
Geiger Counter I Circuit – Circuit Schematic
Geiger Counter I Circuit
The circuit is built around a 4049 hex inverter (Ul), a pair of 555 osciliator/timers (U2 arid U3), two transistors, a Geiger-Muller tube, and a few additional...
Combustible Gas Detector Circuit – Circuit Schematic
Combustible Gas Detector Circuit
THE GAS SENSOR is mainly composed of tin dioxide on a ceramic base; the resistance of the sensor varies depending on the concentration of reducing gases in the...
Explosive Gas Detector Circuit – Circuit Schematic
Explosive Gas Detector Circuit
A gas sensor (TGS823 from Allegro Electronics, Cornwall Bridge, CT 06754) conducts in the presence of explosive gases. U5 is a voltage-to- frequency converter ...