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deciding between two BCD signals

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carbon dude oxide:
hello.
im currently making a clock but i do not wish to have a micro controller in it. i have two BCD signals, one for the clock and the other cycles threw 0-9 rapidly what i am trying to do is switch from the clock to the cycle BCD for 10 seconds then return back to the original BCD input. How would i do this without relays as i would like it to be silent :)   (by relays i mean 2 DPDT to switch from 1 BCD input to the other and then back again)

any help would be brilliant thanks :)

baljemmett:
Presuming that your BCD signals are at a sensible logic level, something like the 74*157 would do most of it -- the '157 is a quad 2-input multiplexer, so it takes two four-bit inputs and outputs one or the other depending on the state of a 'select' input line.  Then you'd just need to drive that input with a 10-second pulse, which you could generate however you like -- for instance, with the old favourite 555 timer.

carbon dude oxide:
thats brilliant thanks :D

also how would i make a 555 timer do a 10 second pulse?

SeanB:
If it is a clock why not use a TTL counter and drive it off the 1Hz clock that you must already have there. Plenty of TTL decimal or hex counters to choose from. Even a 4017 will work.

carbon dude oxide:

--- Quote from: SeanB on January 10, 2013, 05:09:41 pm ---If it is a clock why not use a TTL counter and drive it off the 1Hz clock that you must already have there. Plenty of TTL decimal or hex counters to choose from. Even a 4017 will work.

--- End quote ---

Im going to be using some 74HC390 chips to drive my clock but because there nixie tubes and not LED displays they can get cathode poisoning so to get around this without using a programmable IC  im going to have 1 set of BCD for each tube to control the time and this will be on a 1Hz pulse ect and to prevent cathode poisoning i am going to make the digits cycle through its number repeatedly for 10 seconds which is where the second lot of BCD's come into play so on the hour i need it to switch to the cycle bcd and then after 10 seconds switch back to the clock bcd.

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