novice help 555 timer - Electronic Circuits Projects Diagrams Free

wfontjr · 24th December 2007, 04:34 AM

i was trying to build a timer with a 30 second on and a 3 minute off, i tried using the circuit below on kpsec.com, the one using a diode to get less than a 50% duty, i used r2=1.2M, r1=0.2M and c1=220uF according to the calcs on that page. The output stays on, does not cycle, whats wrong? i also tried it with c1=47uF, same result

if i change out c1 to 10uf the timer will cycle about 1 sec on and 8 secs off

http://www.kpsec.freeuk.com/555timer.htm

**Nigel Goodwin** · 24th December 2007, 07:43 AM

555 timers are very limited as to maximum times, in this case the leakage in the 220uF is probably more than the current available through the 1.2Mohm - you could try using a tantalum capacitor?, this is an application where they really are better.

wfontjr · 24th December 2007, 01:25 PM

thanks for the help

Hero999 · 24th December 2007, 02:12 PM

What are you using it to control?

A relay, LED, piezo buzzer etc.?

Just omit the diode and wire the load from pin 3 to +V instead of 0V.

wfontjr · 24th December 2007, 06:17 PM

i have it on an led for testing, i planned on using in on a relay to start/stop a livewell pump

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24th December 2007, 04:34 AM	(permalink)
wfontjr	novice help 555 timer i was trying to build a timer with a 30 second on and a 3 minute off, i tried using the circuit below on kpsec.com, the one using a diode to get less than a 50% duty, i used r2=1.2M, r1=0.2M and c1=220uF according to the calcs on that page. The output stays on, does not cycle, whats wrong? i also tried it with c1=47uF, same result if i change out c1 to 10uf the timer will cycle about 1 sec on and 8 secs off http://www.kpsec.freeuk.com/555timer.htm

24th December 2007, 07:43 AM	(permalink)
Nigel Goodwin	555 timers are very limited as to maximum times, in this case the leakage in the 220uF is probably more than the current available through the 1.2Mohm - you could try using a tantalum capacitor?, this is an application where they really are better. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

24th December 2007, 01:25 PM	(permalink)
wfontjr	thanks for the help

24th December 2007, 02:12 PM	(permalink)
Hero999	What are you using it to control? A relay, LED, piezo buzzer etc.? Just omit the diode and wire the load from pin 3 to +V instead of 0V. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

24th December 2007, 06:17 PM	(permalink)
wfontjr	i have it on an led for testing, i planned on using in on a relay to start/stop a livewell pump