transistor used as a button

it`s not a Bad idea, but the use of a 4016 or 4069 would have probably been better and more like an actual switch.

you`ll have to get the timing right too (within reason) else you could either Miss the scan or hit it twice for instance.

it May be an idea to also bias the transistors base down to deck to preclude any spurious triggerings/noise.

The 4016 is a great idea- exactly the thing I was looking for.I will see if I can find one..or two couse i need like 7 of these.

So this works like a switch - two pins for  pin4 and pin5 and a 3rd pin going into a digital pin, right?

yes, it`s just like your transistor idea in principal, but will be seen more like a propper key press, and of course it`s bi-directional, so it doesn`t matter what side goes to where (unlike a transistor).

the 74125 will do the same and there is 6 of them on a chip, but these Are directional, so you`ll need to know the Scan lines from the inputs, and of course these are 5v only devices.

Thanks for the idea, too.  I'll give this chip a try.

I had been looking to control power to an Arduino shield recently.  I started by trying to use a transistor as a switch but could not get it working reliably (prob just due to my ignorance of proper biasing, etc).  I ended up using a 5v reed relay which has worked great.  However, I've felt it's not very efficient solution, especially since the whole point of selectively cutting power to the shield was to save battery life.

Cheers,

Drew

well, this chip does have limitations in that there is a small resistance across the switch when "closed" and natually it`s current carrying capacity will be significantly less than that of a metal-on-metal contact (as in your relay).

but they`re cheap enough, and worth carrying in your arsenel of parts even if it doesn`t quite work out for you in That particular application.

Ah, good point about the current.  The shield has a wifi radio which uses up to 210mA max at 3.3V.  That exceeds the current and power dissaption ratings for the 4016 variants I just looked up.  Anyways, I'll keep in mind for future endevors like you advised.

I wont have any problems with the current right, its a keyboard after all .. it cant be using more than 20-40mA per button ..i think

Oh and where can I find one

so as to be without bias, here`s the 1`st on ebay I found just:rhttp://www.ebay.co.uk/itm/2x-CD4016-HCF4016-Quad-Bilaterial-Switch-C-MOS-IC-/180710504134?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2a132f76c6

and no, you could drive several keyboard switches with a single switch, you`ll be fine

thanks,oh and what does bias mean