View Full Version : Dual Teensy Keyboards help....

02-18-2013, 08:44 PM

I'm making a box containing 2 Teensy boards configured as keyboards that will be triggered by a grand total of 3 buttons. Each Teensy will be connected to a separate individual computer.

In the past when I've done something similar, I have used a SPST switch which triggers a MOSFET solid state relay which in turn makes the button press to both keyboard circuits - in the past (before I discovered the Teensy boards) I hacked an existing keyboard matrix and fudged it to work.

Anyway, back to my current little project....

I've had the pcbs made, I've soldered everything and it almost works. I'm taking a 5V feed from the 'main' Teensy and routing that to each SPST switch. When pressed each switch triggers a bank of 2 MOSFET SSR - one triggers a LED as a visual feedback, and the other SSR completes the circuits to trigger the key presses on both Teensys. But in this case nothing is being registered on either Teensy - the LED lights so I know the SSRs seem to be working, but my Teensys just sit there idly doing nothing...Leaving me stumped!

I've checked the continuity with my multimeter, the SSRs are working as they should but nothing seems to happen with the Teensys. I've doubled checked all solder joints, in fact I've resoldered a few times to make sure but nothing works... I've also uploaded a different hex file that I know works from a previous project and that works so I guess the Teensys are good....

I'm using Avago ASSR-1228-302E SSRs datasheet here (http://www.farnell.com/datasheets/358205.pdf)

Would I be correct that the SSRs I'm using need to 'see' a load on it's contacts and that the Teensy pins I'm using aren't providing any load? So if I were to add a resistor somewhere along the line would the general consensus be that it would work? I guess that when I've checked continuity with my multi meter that acts as a resistive load which is why it all seems to, in theory, check out OK

If a resistor is the correct route, the next question is what value resistor would I need (I can't seem to find any values for the maximum mA per pin - I'm guessing 5-10 mA to be safe? ) and would that mess up how the Teensy works as a keyboard?

Thanks for any help!

02-18-2013, 09:33 PM
Seems to me you're hardware is overly complex for what you're trying to do. The teensy's are perfectly capable of directly using button inputs and driving LED's. The code and wiring to do this is actually in the tutorials. It seems like you'd need very little hardware other than three push buttons, three led's, and three current limiting resistors for the LED's. The rest, including you're keyboard output, would all be done in code.

02-18-2013, 10:34 PM
It is a bit overly complicated - I originally wanted to use a DPDT or DPST switch, but I just couldn't find one that was suitable (LED lit and no more than 16mm total height), hence a SPST (LED lit and about 15mm high) and the SSRs to keep both Teensys isolated from each other. My first attempt at this type of project involved 2 keyboards and a SPST switch to allow simultaneous pressing of a space bar - both PCs freaked out so since then I've always used a double pole switch to stop that from happening....

02-18-2013, 11:06 PM
Well, i'm assuming you'd have the teensy's emulating USB keyboards, so since you're using two teensys, isolation shouldn't be an issue on the PC side. It shouldn't matter if you have one SPST feeding inputs on both teensy's or not, though you'd have to pick one or the other teensy to drive the LED. You don't need both feeding that.

02-19-2013, 02:01 AM
Have you tried measuring the voltage at the Teensy pin, while pressing and releasing the switch?

You might need a real pullup resistor, like 1K. If the SSR and pullup resistor is delivering a signal that changes when you press the button, then it should work. You can check the signal with a voltmeter.

03-01-2013, 07:22 PM
Apologies, I've been away working, so I've not yet had much chance to do anything....

But, I've just noticed that it appears I've been an idiot and incorrectly wired up my pins for the rows :rolleyes: So I'll get a new board made up, unless I can do some pcb surgery, and hopefully that will sort out my issues.

you'll find me in the corner wearing a hat with a big D written on it! :o