I'm looking to turn on a relay threw a logic signal from a keypad. I need to know if there's a programmable keypad I can buy (off the shelf) that already has all the circuitry to program in a number (say 4 digits) and have a TTL type output that will go high when the correct number is typed.

This is my first post here and I've never been on this site so if I'm posting in the wrong spot I apologize.

Any help is appreciated.

 

I don't know of an existing programmable keypad, but a 4x4 would be easy to set up as you have suggested if you just hook it up to a uC. Have the uC watch for the correct code on the keypad, and respond accordingly.

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-Gandledorf

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I don't know of an existing programmable keypad, but a 4x4 would be easy to set up as you have suggested if you just hook it up to a uC. Have the uC watch for the correct code on the keypad, and respond accordingly.[/quote]

I don't have a good feel for how easy (or difficult) this really is. I've got almost no experience writing code.

 

If you have little experience it may be hard, but you are going to need to do some programming to get a project like this done.

Basically, you set up the 4x4 keypad to come in on an eight bit port, then map the byte to a keypress (be sure to debounce as well, either software or hardware). Store the last X bytes in RAM, and compare the sequence with the code in EEPROM. When they match, trigger another I/O line to send the signal that the code was inputed correctly, and have this trigger your relay, etc.

__________________
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-Gandledorf

Come visit http://groups.yahoo.com/group/laser_design a group dedicated to help designers build electronic games, and design optical combat systems.

 

If I can't find what I'm looking for and have to build and code myself can you lead me to some kind of a source to get me started.

Would an 80C51 be good for something like this?

 

I personally like the AVR uC line. They are low cost, have FLASH memory, run on low power, and are good general uC's.

For your purposes, I might suggest an AT90S2313, it has some basic functions, but no excess, some RAM, and some EEPROM.

__________________
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-Gandledorf

Come visit http://groups.yahoo.com/group/laser_design a group dedicated to help designers build electronic games, and design optical combat systems.

 

Have a look at my PIC turorials at http://www.winpicprog.co.uk, I have a tutorial on reading a HEX keypad and implementing a simple code lock.

 

www.maplin.co.uk can supply a readymade keypad entry panel. Do a search for K6400 keycode lock. The price is £25.

Also this link gives a circuit using two logic chips:-

http://www.electronicsforu.com/efyli...00/jancir2.htm

 

If it's still available, the UA3730 is a dedicated chip for the job.

 

Also, this month's edition of circuit cellar has exactly what you're looking for.