help

hi if some one can please help me because i need the circuit diagram for a 5 minute delay off timer

Posted by haripost on 25/05/2003, at 14:48 GMT

The monostable circuit

To create a delay you need a monostable circuit. Take a look at the 555 monostable circuit at www.eleinmec.com/article.asp?4

To make a 5 minute delay, you will need to use a large value timing capacitor and a smaller value timing resistor.

In theory, a 1000uF capacitor and a 270kOhm resistor should give you a delay of 297 seconds, or 4.95 minutes.

Posted by Tim Surtell on 26/05/2003, at 09:09 GMT

Help with 555 Monostable

To get reliable results using the 555 monostable in long time delays I would follow the advice below: 1. Timing capacitor leakage will place an upper limit on the value for electrolytic caps -usually around 100uf (for (the recommended) tantalum electrolytic type). The upper value for the resistor is probably 1M ohms. An alternative using higher values of timing resistor is probably the CMOS version of the 555 driving an external transistor (available current is lower(half 7555 or twentieth 1/20 TS555) of normal.
2. Supply decoupling (logic practise) or use of regulated supply is probably recommended.

Posted by Anonymous on 07/01/2011, at 22:53 GMT