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rocket lucher

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New Member
i was wondering ho to build a rocket luncker with 2 digits and time mesured in seconds, so a limit to 99seconds.
i was thinking of using 2 4029 u/d counters+2 decoders + a 2 digit display
turn the clock off, turn the counters to up, or even down, use 2 buttons to set the numbers on the digits tu set the countdown time, turn the counter to down, turn the clock on and start it counting. as a clock source ill use a 555, because i dont need to accurate mesurement.
but here comes the question: how do i do the trigger mecansim to set it off when i have 00 on the display. i thought to use a 8 input(4 bits form each counter) nand gate wich will have a H output when all the inputs are L.
but think of how hard it will be to build the pcb. there are lot of connections to do.
anyone got any other ideas? maybe using different type of counters?
i could use a simple down up counter like the 4017 and just use a simple trigger,and a clack signal with a frequency like 0.5Hz or maybe a bit less.


Active Member
could use a simple down up counter like the 4017
4017 is only Up counter not down.

By the way if you are asking for some other ideas how about doing it with uC. I have already made a 2 digit count-down timer for exercise machine using 89C2051 uC and the PCB is just 7cm x 7cm. You can even find PIC based projets on google. There are many such lying around.


New Member
thanks. what i wanted to say about the 4017 is that i could do something like start on Q0 and when it gets to Q9 it lunches the rocket.
and what i want to do is with normal, non-programable circuits.
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