novice help 555 timer

[wfontjr]

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]

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]

thanks for the help

 

[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.

 

[wfontjr]

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