Cut Phone Line Detector

A while ago I got an email asking for the schematic of a circuit to detect cut phone lines. It didn't take me long to find this circuit inElectronics Now. When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a security system.

Schematic

Parts

Part Total Qty. Description Substitutions R1, R2, R3 3 22 Meg 1/4 W Resistor R4 1 2.2 Meg 1/4 W Resistor C1 1 0.47uF 250V Mylar Capicitor Q1 1 2N3904 Transistor 2N2222 Q2 1 2N3906 Transistor Q3 1 IRF510 Power MOSFET D1 1 1N914 Diode Load 1 See "Notes" MISC 1 Wire, Phone Connectors, Circiut Board

Notes

1. The "Load" can be a relay, lamp, motor, etc. The circuit can also be connected to a security system to sound an alarm in case the phone line is cut.
2. If the circuit is connected to a security system or other circuit, both circuits must be electrically isolated from each other using an opto-isolator, relay, etc. This also means that the Cut Phone Line Detector must be powered by a seperate 9V supply.

Water Detector With Sump/Bilge 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 through a set of probes. An internal comparator compares the resistance of the probes to an internal reference. When the resistance between the probes is low (indicating the presence of water or other conductive liquid) then the IC triggers it's output. An AC signal avoids electroplating and corrosion problems that are common when DC is used. To provide an adjustable delay hysteresis to avoid cycling the pump, a timer based around the 555 is used a range of about 5 seconds to two minutes. In this way the pump will stay active for a set amount of time even if the fluid level is below that of the probes.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 470 Ohm 1/4 W Resistor R2, R4 1 10K 1/4 W Resistor R3 1 6.8K 1/4 W Resistor R5 1 1 Meg Linear Taper Pot R6 1 51K 1/4 W Resistor C1 1 470uF 35V Electrolytic Capacitor C2 1 0.001uF Ceramic Disc Capacitor C3 1 0.05 uF Ceramic Disc Capacitor C4 1 20uF 35V Electrolytic Capacitor C5 1 6.8uF 35V Electrolytic Capacitor C6, C8 2 0.01uF Ceramic Disc Capacitor C7 1 100uF 35V Electrolytic Capacitor U1 1 LM1830 Fluid Detection IC U2 1 555 Timer Q1 1 2N5305 NPN Power Transistor D1, D2 2 1N4148 Signal Diode D3 1 1N4002 Rectifier Diode K1 1 Relay With 12V Coil (See Notes) S1 1 SPST Switch PROBES 1 Stainless Steel Probes (See Notes) MISC 1 Case, Knob, Board, Wire, Sockets For U1 and U2

Notes

1. The probes should be made of stainless steel and mounted in a non-conductive fixture. Stainless steel nails, bolts or welding rod will make ideal probes. Good non-conductive materials are Lexan, plexiglass or plastic. The probes are to be placed at the liquid level at which you wish the pump to turn on.
2. K1 should be chosen according to the requirements of the pump. If you are running a 12V pump then common automotive relays will work fine. If you are running a mains powered pump then you will need to make sure the contacts are rated accordingly.
3. S1 provides a manual pump switch.
4. R5 adjusts the on-time of the pump once moisture has been detected. It is adjustable from approximately 5 seconds to approximately 2 minutes.
5. The probes should be cleaned periodically to assure reliable operation.

Light/Dark Detector

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 100K Pot Q1 1 2N3904 NPN Transistor 2N2222 Q2 1 NPN Phototransistor RELAY 1 9V Relay MISC 1 Board, Wire, 9V Battery Snap (if battery used), Knob For R1

Notes

1. R1 Adjusts sensitivity

Simple Lie Detector

Here's a simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth. It is not as sophisticated as the ones the professionals use, but it works. It works by measuring skin resistance, which goes down when you lie.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 33K 1/4W Resistor R2 1 5K Pot R3 1 1.5K 1/4W Resistor C1 1 1uF 16V Electrolytic Capacitor Q1 1 2N3565 NPN Transistor M1 1 0-1 mA Analog Meter MISC 1 Case, Wire, Electrodes (See Nots)

Notes

1. The electrodes can be alligator clips (although they can be painful), electrode pads (like the type they use in the hospital), or just wires and tape.
2. To use the circuit, attach the electrodes to the back of the subjects hand, about 1 inch apart. Then, adjust the meter for a reading of 0. Ask the questions. You know the subject is lying when the meter changes.

Rain Detector

This circuit uses a sensor made of a small piece of etched PC board and a simple SCR circuit to detect rain and sound a buzzer. The SCR could also be used to activate a relay, turn on a lamp, or send a signal to a security system.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 1K 1/4 W Resistor R2 1 680 Ohm 1/4 W Resistor D1 1 1N4001 Silicon Diode BZ1 1 12V Buzzer S1 1 SPST Switch SCR1 1 C106B1 SCR 106CY SENSOR 1 See Notes MISC 1 Board, Wire, Case, PC Board (For Sensor)

Notes

1. The sensor is a small piece of PC board etched to the pattern showen in the schematic. The traces should be very close to each other, but never touching. A large spiral pattern would also work.
2. Make sure to use a loud buzzer.

Air Flow Detector

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 100 Ohm 1/4W Resistor R2 1 470 Ohm 1/4W Resistor R3 1 10k 1/4W Resistor R4 1 100K 1/4W Resistor R5 1 1K 1/4W Resistor C1 1 47uF Electrolytic Capacitor U1 1 78L05 Voltage Regulator U2 1 LM339 Op Amp L1 1 #47 Incandescent lamp with glass removed (See "Notes") D1 1 LED MISC 1 Board, Wire, Sockets for ICs, etc.

Notes

1. The glass will have to be removed from L1 without breaking the filament. Wrap the glass in masking tape and it in a vise. Slowly crank down until the glass breaks, then remove the bulb and carefully peel back the tape. If the filament has broken, you will need another lamp.