i need some help with with a timer circuit that will hold the output high for about 30 seconds when power is applied and then go low indefinetly until it is powered down and turned on again
you can use 555 in monostable mode, use the timing resistors to select 30s, when there is a signal on the input pin the output will be high for 30s and then low again until again gets a signal,
you can input a pulse and the circuit would output high for 30 secs
for the resistor and capacitor values for timing u can use the program available here
You can use 4001 or 4011 cmos gates or 4049 inverters etc.
for faster output switching time add 2 additional gates serially to signal
without transistor and relay , output is over C2.
Output is logic 1 at start
Inverting output connect one inverting gate more.