03-05-2015, 03:54 PM
This may be a waste of time, David, but have you checked which way around you've wired the relay? Most of these miniature types are two-way and if this is so, a simple answer is that you've wired the thing into a 'normally on' configuration. This is easily proved as if I'm correct in my assumption, the timer should switch off after the requisite period (12 seconds).
However... is your track layout a mirror image of the tracks? If not you have connected pin 2 to pin 3 of the 555.
Finally, all else failing, there must be sufficient voltage appearing at pin 3 even when 'low' to operate the relay. Very hard to imagine that, but a small value series resistor might be an answer.
I can see no problem with the schematic of the timer, nor with the dual timer/astable circuit. Both should work perfectly.
Tony
However... is your track layout a mirror image of the tracks? If not you have connected pin 2 to pin 3 of the 555.
Finally, all else failing, there must be sufficient voltage appearing at pin 3 even when 'low' to operate the relay. Very hard to imagine that, but a small value series resistor might be an answer.
I can see no problem with the schematic of the timer, nor with the dual timer/astable circuit. Both should work perfectly.
Tony
