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Fluid Level Detector (LM1830N)
The IC is ideal for detecting the presence, absence or level of water or other conducting liquids. A detector determines the presence or absence of fluid by com...
Two buttons Safety relay – Circuit Schematic
Two buttons Safety relay
This circuit turns on a relay when two buttons are pressed at the same time.The relay backs off after few seconds, then the buttons have to be released and pres...
Detection for trains on model railway – Circuit Schematic
Detection for trains on model railway
This light valve can be used for example to detect trains on model railway or a lap counter at the close racing. D3 receives a constant stream of power built a...
Water Detector with Buzzer – Circuit Schematic
Water Detector with Buzzer
This is a simple circuit that can be used as a detector for water, such as a bath full detector. The terminals 'sensor' is connected to the probe. This may cons...
Wet soil tester with LED – Circuit Schematic
Wet soil tester with LED
This is a very simple circuit that can be used to test whether a pot is dry or not. When the two probes are inserted in wet soil, then the resistance between th...
Toy Train rail detector circuit II – Circuit Schematic
Toy Train rail detector circuit II
This circuit can detect whether a train in a particular drive. The output is TTL and CMOS compatible and can be processed by such a computer. The simple circuit...
Toy Train rail detector circuit – Circuit Schematic
Toy Train rail detector circuit
This circuit must be used between the drive voltage of such a transformer and track. On JP1, the transformer is connected to JP2, the rails are connected to JP3...
Photo detector using LED – Circuit Schematic
Photo detector using LED
Here's a circuit that takes advantage of the photo-voltaic voltage of an ordinary LED. The LED voltage is buffered by a junction FET transistor and then applied...
AC current Detector schematic – Circuit Schematic
AC current Detector schematic
This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of t...
Light Activated switch with Relay – Circuit Schematic
Light Activated switch with Relay
This is same circuit as above with the addition of a photo resistor to trigger the flip flop instead of a push button. The bias resistor in series with photo re...
12V Electronic Thermostat with Relay – Circuit Schematic
12V Electronic Thermostat with Relay
Here is a simple thermostat circuit that can be used to control a relay and supply power to a small space heater through the relay contacts. The relay contacts ...
Whistle on / off switch – Circuit Schematic
Whistle on / off switch
This is an extension of the CMOS toggle flip flop circuit shown in the "Circuits controlling relays" section with the addition of two bandpass filters and conde...
Fan Failure Detector circuit – Circuit Schematic
Fan Failure Detector circuit
The cooling is not only a PC using a small fan with an electronic commutator [1]. A special feature of these fans is that their removal is less dependent on the...
Optical switch detector with 555 – Circuit Schematic
Optical switch detector with 555
When the phototransistor is stroken by IR light it conducts and the voltage between the 1Mohm resistor(arbitrary) and the phototrans drops from VCC to lower val...
Video Activated Relay – Circuit Schematic
Video Activated Relay
This simple circuit from the May 1996 Think Tank column of Popular Electronics activates a relay when it senses a composite video signal. This allows you to use...
Moisture detector with pump controller – Circuit Schematic
Moisture detector with pump controller
This moisture detector with pump controller is built around the special purpose LM1830 IC. The LM1830 is designed to detect moisture by passing an AC current th...
Thermometer with 10 LED scale – Circuit Schematic
Thermometer with 10 LED scale
This LED thermometer is designed for in home use, to read temperatures between about 60 and 78 degrees Fahrenheit. It is based around a precision temperature se...
Precision thermocouple signal amplifier – Circuit Schematic
Precision thermocouple signal amplifier
This circuit greatly expands upon the capabilities of circuit 02. A thermocouple signal is quite small, and the long thermocouple leads often induce quite a bit...
Battery Current Sensor – Circuit Schematic
Battery Current Sensor
These controllers have an inhibit input and the effect of shorting this down to ground is to turn down the internal demand speed. So with the battery current li...
Current Loop Sensor Interface – Circuit Schematic
Current Loop Sensor Interface
This is a very simple circuit to interface a current loop sensor to an input which is designed for a voltage, such as that from a standard potentiometer. This p...