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any idea son how to make a digital, adjustable timer that i could use to launch a model rockets?

 have a 4 channel fire control platform. i would like to change one of the channels to a digital fully programable digital timer

Go to the Dollar store and get a digital kitchen timer. Use the output to the "beeper" to trigger a one-shot into a latching relay. The output of the relay will be to the model rocket ignitor. To reset the relay, remove power to the relay coil.

Be careful when the timer is open. The display can get knocked loose and if you don't have it lined up correctly on the contact strip, it won't display properly.

Qa
THe output of the timer is not likely to have the power to ignite the rocket. The timer will have to operate a relay that will close the circuit to ignite the rocket.
That's what I alluded to with "Use the output to the "beeper" to trigger a one-shot into a latching relay. The output of the relay will be to the model rocket ignitor."

So: timer beeper output->one-shot->latching relay.

The one-shot will probably need a transistor on the output in order to beef up the current to trigger the latching relay.

The one-shot might not even be necessary, i.e.: timer beeper output ->non-inverting transistor amplifier->latching relay.

Just trying to use inexpensive pre-made stuff for some of the more intricate parts (timer). The most expensive thing I list is probably the latching relay. And that can be reduced in price by using an ordinary relay wired to self-latch.

(All of these things I name have schematics/how-to's/tutorials on the web. A quick search for each term will net a winner.)

Options,options...

Qa
I guess I was still asleep when I read your first post. I don't remember see anything about a relay in it.