Keypad matrix

Hi, i'm building a circuit with a keypad and really wanted the type with 13 terminals, 1 common and one for each of the 12 buttons.

However, i could only get the matrix type with 7 terminals.

How do ppl usually use these?

Is there a chip i can run it through so that i can have 12 different outputs depending on which button is pressed?

Any advice would be extremely welcome

Cheers.

The usual way is to scan them using a micro-controller, which usually does everything else as well.

What are you wanting to use it for?.

it's for an immobiliser circuit for my car. You press the buttons in sequence and it cascades through to switch a relay. I don't really know anything about pic stuff but would be interested to learn.

I presume that i could program a chip that when it received the correct sequence it could give an output to switch a relay. This would be much simplier and take up less space.

What sort of cost would i be looking at to get the right equipment??

Any pointers on where to go would be useful as well. The only electronic place near me is Maplins and i know they do it. Is it any good? What sort of stuff would i need?

thanks.

Jackboy said:

it's for an immobiliser circuit for my car. You press the buttons in sequence and it cascades through to switch a relay. I don't really know anything about pic stuff but would be interested to learn.

I presume that i could program a chip that when it received the correct sequence it could give an output to switch a relay. This would be much simplier and take up less space.

Click to expand...

You could do it all with a PIC 16F628 very easily, there's even code for a keypad lock in one of my tutorials at http://www.winpicprog.co.uk. The tutorial uses a 4x4 keypad (but shows the changes for 3x4), which doesn't leave many pins spare (one unused on the LCD board). For that reason the tutorial doesn't actually switch anything, but it would be very easy to add.

You don't need an LCD display on it, but it does look nice and makes it easy to use as well - and it looks GOOD!, which I'm presuming is your reason for wanting to do this?.

Any pointers on where to go would be useful as well. The only electronic place near me is Maplins and i know they do it. Is it any good? What sort of stuff would i need?

Click to expand...

You can get a PIC16F628 from Maplins, I'm not sure about a PIC programmer - they did do one, but it was a copy of the very old David Tait design, and not one of the newer updated ones. Have a look at **broken link removed** for a better version, which can be used with my free software. As a kit it's only £10.95 including VAT.

Hi im doing a similar projsct and have been looking for a way to connect up a 12 key keypad to my cicuit, i have found these sites which you may find helpfull:

**broken link removed**

http://www.geocities.com/SiliconValley/Orchard/6633/keypad.html