Showing posts with label timer. Show all posts
Showing posts with label timer. Show all posts
Monday, August 25, 2014
Extend Timer Range For The 555
Anyone who has designed diagram using the 555 timer chip will, at some time have wished that it could be programmed for longer timing periods. Timing periods greater than a few minutes are difficult to achieve because component leakage currents in large timing capacitors become significant. There is however no reason to opt for a purely digital solution just yet.
The schema shown here uses a 555 timer in the design but nevertheless achieves a timing interval of up to an hour! The trick here is to feed the timing capacitor not with a constant voltage but with a pulsed dc voltage. The pulses are derived from the un smoothed low voltage output of the power supply bridge rectifier.
Extend Timer Range For The 555 Circuit
The power supply output is not referenced to earth potential and the pulsing full wave rectified signal is fed to the base of T1 via resistor R1. A 100-Hz square wave signal is produced on the collector of T1 as the transistor switches.
The positive half of this waveform charges up the timing capacitor C1 via D2 and P1. Diode D2 prevents the charge on C1 from discharging through T1 when the square wave signal goes low. Push-button S1 is used to start the timing period. This method of charging uses relatively low component values for P1 (2.2 MΩ) and C1 (100 to 200 µF) but achieves timing periods of up to an hour which is much longer than a standard 555 schema configuration.
The schema shown here uses a 555 timer in the design but nevertheless achieves a timing interval of up to an hour! The trick here is to feed the timing capacitor not with a constant voltage but with a pulsed dc voltage. The pulses are derived from the un smoothed low voltage output of the power supply bridge rectifier.
Extend Timer Range For The 555 Circuit
The power supply output is not referenced to earth potential and the pulsing full wave rectified signal is fed to the base of T1 via resistor R1. A 100-Hz square wave signal is produced on the collector of T1 as the transistor switches.
The positive half of this waveform charges up the timing capacitor C1 via D2 and P1. Diode D2 prevents the charge on C1 from discharging through T1 when the square wave signal goes low. Push-button S1 is used to start the timing period. This method of charging uses relatively low component values for P1 (2.2 MΩ) and C1 (100 to 200 µF) but achieves timing periods of up to an hour which is much longer than a standard 555 schema configuration.
Streampowers
Monday, August 11, 2014
Head light timer circuit 2
This schema is a compact timer schema that will keep the headlights of your car ON for about 1.5 minutes and then turns it OFF.This schema incorporated to your car will help you to access dark places with out the need to come back and turn OFF the head lights.
When the push button switch P1 is pressed the capacitor C1 is charged to the full battery voltage.As a result the transistor Q1 is turned ON ,which in turns ON Q2 which in turns drives the relay K1 to glow the head lights.The relay K1 will remain activated until the capacitor C1 is fully discharged.The time delay of the schema depends on values of C1 & R1 and here it is set to be 1.5 minutes.
Notes.
* Assemble the schema on a good quality PCB or common board.
* The time delay of the schema can be varied by varying the values of R1&C2.
* At most care must be taken while wiring this schema to your car because a wrong connection could cost you a lot of money.
* The capacitor C1 must be rated at least 15V.
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