hi,
The relay coil when switched off will generate a 'back emf' [high voltage] which can damage the 555.
The long wires to the switch can act like an aerial picking up external electrical switching noise,
twist the two wires together about 3 twists/inch.
Also add the caps as shown in this dwg.
These caps should always be fitted to a 555 timer [ or other logic]
they are to suppress electrical noise on the +V/0V lines.
When fitted they MAY fix your switch ON problem. Lets know
Hi Eric, done what u sugested in the last post and it WORKS, I had to use a 470uf as the smaller ones only had a 50% hit rate the larger cap is about 90% hit rate, can i change the res to improve it ? Dont know what size to go to ?
Hi Eric, done what u sugested in the last post and it WORKS, I had to use a 470uf as the smaller ones only had a 50% hit rate the larger cap is about 90% hit rate, can i change the res to improve it ? Dont know what size to go to ?
hi,
Are using the CMOS or TTL version of the 555.?
EDIT:
If you increase the value of the cap, I would add the discharge diode across the resistor.
This will quickly discharge the cap, ready for the next power ON time.
IIRC the CMOS version of the 555 should be OK upto about 470K or so.?