Circuit Diagram Knowledge: Wiring Diagram

Showing posts with label Wiring Diagram. Show all posts

Thursday, October 9, 2014

Active Low Trigger Circuit based Timer IC 555

This is the easy build active low trigger circuit based timer IC 555. The circuit also known as normally closed trigger circuit. 9V DC supply is required to operate this circuit.

This circuit sits Low and the output goes High after the push-button switch is pressed. When the normally-closed push button switch is pressed, it opens and the uncharged 1uF capacitor is going to be pulled to almost 0v rail via the 10k resistor and this will bring pin 2 Low for making output pin 3 High for the period decided by the 22uF capacitor and 100k resistor. If the push-switch continues open, the 1uF will charge via the 100k and at some point the output of the 555 will go low.

But generally the switch has to be pressed for a short period of time in order that the timing parts (100k and 22uF) make the output go High for a short time period.

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Long Time Delays with 555 Timer

This is a Long Time Delays using 555 Timer. In 555 Timer, a function of charging rate of the external capacitor is the timing. This circuit needs expensive capacitors with extremely low leakage. Practically, the components limit the time between pulse to around twenty minutes. To get longer time periods, we can connect both halves in tandem with a “divide-by” network in between. Here is the circuit:
Long

The first timer section is operated in an oscillatory mode. The periods of the first timer is 1/Fo. Then the “divide-by-N” network recieves this signal and will generate the output signal with period of N/Fo. The second half of the 555 is triggered by the output signal of “divide-by-N”. So, the total time is now a function of Fo and N.

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