I need to activate a machine in x hours after turning on a timer.
The machine has tip-touch buttons so I guess I can use the 2 poles of
the start-button while leaving the original circuits connected.
This depends on the maschine, but maybe it is possible, e.g. with a
transistor, parallel to the button.
Does anybody know what circuit I need for this application?
If you have power supply, too, you can use an oscillator and some HC4040 or
other counters. With a LM555, which generates a 100Hz signal, you can delay
more than 40 hours. This is the no-programming solution and useful, if you
have already the counters and an oscillator.
Another nice one-chip solution, but more complicated, is to use a MSP430 or
PIC microcontroller, which are available with integrated oscillator. I
think the assembler program can be written in less than 10 lines. With some
more external components you could implement an adjustable delay, e.g. with
a potentiometer and the integrated ADC of some microcontrollers, or with a
standard digital GPIO by measuring the time needed for charging and
discharging a capacitor with a potentiometer.