Alternate Keypad Interface

bluetooth · Post by **bluetooth** » Mon Jun 16, 2003 9:30 pm

So there are a number of posts and articles about running how powered components (CCFL lighting, fans, etc.) off of low powered GOPs, but what I need is something on the other end of things.

I don't know much about elctronics (I've only taken an intro level EE course), but what I need to do is control the keypad inputs using voltages, not switches.

That is, when I push a key, I get 5v at a max of 1 ma and I need that to trigger the keypad input...I will have six of these. I know this must involve transistors, but I'm not sure how (especially since I don't know exactly how the keypad interface works)

Any help would be much appreciated.

~Adam

SilmarilS · Post by **SilmarilS** » Tue Jun 17, 2003 12:43 am

Okay...now I'm not a king in electronic but it will be something as you will start with your 5v - 1mA and ramp up a little to about 5v - 150mA with a simple transistor and next, you use a relay to contact the keypad input...
but you can't keep the contact close. ex: you cannot press two keys at the same time....

The way the keypad works is that on one pin you have V+ and the other pin is GND...when you switch V+ to GND a keypress is made... But, the keypad interface work as a matrix of row and colomn...just check the MO site to have better explanation of the Keypad connection...

Post by **linear** » Tue Jun 17, 2003 10:24 am

You want the 4066 quad bilateral switch, or one of it's relatives. when it gets a logic HIGH, it closes a switch (actually turns on a couple FETs), so it's ideal for interfacing logic level signals to the keypad headers.

Cheap too, I think I paid $0.25 for mine.

*Tip of the hat to Stig for coming up with this in the first place.

SilmarilS · Post by **SilmarilS** » Tue Jun 17, 2003 11:47 am

I agree with Linear....

very interresting piece of electronic here....easy to use too!

bluetooth · Post by **bluetooth** » Tue Jun 17, 2003 6:23 pm

Ah huh...I saw the 4066 mentioned elsewhere in the forum, but the datasheet link is much appreciated as I couldn't find it before. I knew there must be something out there, prepackaged, that does exactly what I need.

BTW, in case curiosity springs up, I'm interfacing with aQT160 (just got a few yesterday and it was a sinch to get working)...very cool.

Thanks Man.

~Adam

EDIT:
Oh yeah, what is TTL and do I need / want it (I noticed there is a TTL enabled version and a normal version...)

Miles · Post by **Miles** » Wed Jun 18, 2003 10:40 am

Try this link: http://www.philipslogic.com/products/switches/4066/

Very cool app. by the way...you might have to post some pics in our gallery when done...!

Post by **linear** » Wed Jun 18, 2003 3:32 pm

TTL -> transistor-transistor logic, usually meant to indicate +5V corresponds to ON. As opposed to RS-232 or some other signaling scheme where other voltages mean ON or OFF.

QT113H-D was the ones I used. They are active high, so I could close a 4066 directly from the output, no inverter required. Most of the QT11x are active-low. Looks like the 160 is active-high, so you're good to go--that's a new product since I got mine. You're right they are pretty easy to deal with. Be sure to shield the connection to your electrodes and ground the shield.