Timers and timing circuits are used in a wide variety of applications such as digital circuitry and computers. The following schematic shows a very simple delay timer using a single transistor and an R-C timing circuit. This circuit design was used to switch on device via a LED – photocell arrangement (optocoupler) using components R1, C1, D1 and Q1. It produces a delay on powering up to ensure correct sequencing of certain equipment.
Delay Timer Circuit using NE555 Description
C1 charges toward the power supply voltage (12 volts) through R1. When the voltage reaches 9.1 volts, zener diode D1 conducts, forward biasing the transistor Q1, turning it on. At about 9.8 volts, the zener diode and base of Q1 conduct heavily, taking the charging current from C1. When power is turned off, the circuit is reset by C1 discharging through R1 into the now zero voltage supply. The time can be varied by changing R1, C1.
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1 comment for this entry ↓
1 nimantha weerakkody // Jul 24, 2011 at 10:58 pm
on dely timer
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