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Wednesday, September 3, 2014

Simple ON OFF Touch Switch with 555 Schematic

This simple ON OFF touch switch schema is based on the well known timer IC 555 (IC1), which drives a relay that acts like a switch. The metal surfaces can have what form we want, but it should be clean and very close to the schema.

555 ON/OFF Touch Switch Schematic

Parts List
R1 = R2 = 3.3M
R3 = 10K
R4 = 1K
C1 = 10nF
D1 = 1N4007
Q1 = BC547
IC = NE555
12V relay

Wednesday, April 10, 2013

High and Low Mains Voltage Cut Off Circuit

Are you having problems with your input Mains supply? That’s common problem associated with our input mains AC line, where a high and a low voltage conditions are quite frequently encountered by us. The simple circuit shown here can be built and installed in you house electrical board for getting a 24/7 safety from the possible dangerous AC voltage conditions. The circuit keeps the relay and the wired appliances as long as the mains input stays within a safe tolerable level and switches the load OFF the moment a dangerous or unfavorable voltage condition is sensed by the circuit.

Parts List

R1, R2 = 1K,

P1, P2 = 10K Preset,

T1, T2 = BC547B,

C1 = 100uF/25V,

D1 = 1N4007

RL1 = 12V, SPDT,

TR1 = 0-12V, 500mA

Tuesday, April 9, 2013

555 Timer Circuit With Variable On Off Times

This circuit enables the on/off times of a 555 timer to be independently varied over a wide range. This is not possible with a conventional 555 circuit with the RC network being charged from the positive supply rail and discharged via pin 7. Instead, the capacitor at pins 2 & 6 of IC1 is charged and discharged from the output at pin 3. Furthermore, the charging and discharging circuits are different, being isolated by diodes D1 & D2.

Circuit diagram:

555 Timer Circuit Diagram With Variable On/Off Times

Therefore the capacitor at pins 2 & 6 is charged via diode D2 and trimpot VR2 and discharged via D1 and trimpot VR1. With this arrangement you can have very long on times combined with very short off times and vice versa, or you can adjust the duty cycle to exactly 50% and so on. This circuit also employs a second 555 timer (IC2) as an inverter so that complementary pulses are available, if required. If not, delete IC2.

Author: A. Davies - Copyright: Silicon Chip Electronics