interfacing to the keypad

Post by **linear** » Tue Dec 10, 2002 10:26 pm

I'm interested in using TTL to interface to the keypad. Are there more specs available on how it works than what's in the manual? I understand the 'row pin shorts to column pin' concept pretty well, I'm trying to figure out how a device that generated TTL outputs could drive the keypad inputs.
(Without relays)

Stig · Post by **Stig** » Wed Dec 11, 2002 12:17 pm

You could use the same principle I used for the IR-to-keypad-circuit I made earlier. It used 4066s as switches and they can be controlled by TTL, should be...

Stig

Post by **linear** » Wed Dec 11, 2002 2:23 pm

Looks promising.

Post by **Aniso** » Thu Dec 12, 2002 12:31 pm

Like Stig says, that's the only way. The key scan works by making the previously grounded pins high one at a time to find out which one is making the previously high pin to be now low. So, you *must* short two pins together. An analog switch attached to the TTL input which connects a column and a row is (I think) the best solution. Though, I suppose a simple transister could do the job... I think... Might require a pullup resister on the row... not sure.

Post by **linear** » Thu Dec 12, 2002 12:56 pm

Thanks for the input, Aniso, it gives me a good direction.

Since a 4066 costs less than a buck, I'll take a stab at it that way

Plus I can think of a couple other ingenious uses for it...