MESA 7i73 - Matrix keyboard - use of diodes?

Hi Peter and everyone...

I put 1n4148 diodes across all the switches of my matrix of cherry MX key switches, which I am interfacing with a 7i73. The diodes test at about 0.52V fwd bias.
I have checked and double checked the polarity, and wiring, running through all with a lab PSU set for 3.3VDC, and a blue diode. All switches work, with the same polarity, and the test LED lights up, but insufficient current flows, to show up on the lab PSU's ammeter or power display. Reversing the polarity, the test LED does not light up.

It turns out that there are a few of the little Cherry MX break out boards I used, where I failed to cut the diode jumper. When I test those switches, my blue test LED glows brighter, and I get 40mA of current and 0.15W indicated on the PSU.

When I connect up the 7i73, those switches with the jumpered diodes are the only switches which are recognised in LinuxCNC.

I dont really understand why the 1N4148's are flowing a enough current to light the LED, but insufficient to trigger the 7i73 or show a current/power flow on my lab PSU.

Should I remove / jumper all the diodes from a 7i73 installation? I added them based on a Cherry MX keys how to article, but those are normally from gamers, and my CNC never needs fast typing of function buttons.

Cheers,
Mark

The 7I73 does not require diodes in its keyboard matrix.
(diodes should work but may not be in the direction you expect)

Wow, thanks for the prompt response.

I guess I'll just remove/ jumper them then, rather than stay blocked by this point.
Cheers,
Mark

I have +3.3V on the terminal I connect to 7i73 P1-3, negative on P1-11. A blue LED in series lights up mid bright when I close the switch . Insufficient current for the 7i73 or to show up on the PSU's power meter.

If I jumper the switches 1N4148, the test light is brighter, the 7i73 sees the switch and PSU shows 0.15W of power. It seems to me that the circuit is right, but the 1N4148 is is not flowing enough current.

The 7I73 row outputs (KEY0..7) sink current
from the column inputs (KEY8..15) so a diode
would need to have its cathode pointing towards
the row outputs to work.

The current involved is tiny (~300 uA)

Okay, then I have all the diodes backwards, as I understood an output as where the 3.3V is supplied from,  and the inputs are where the hi or lo state is read.

Thanks for clarifying that.

If I hadn't used diodes, it would not have been an issue. Since I used separate pin head connectors for the inputs and outputs, I will see if there is enough slack in my wires to just switch them, and transpose the pin assignment matrix.

... Looks like there was enough slack in those wires.

The above is why I asked in your other thread about the multi-key input for the joystick.  Was wondering if you figured some way to use diodes so that multiple inputs worked reliably.

If it helps, I've attached a photo of my first 7i73 matrix keypad with diodes (hand-wire, 4x8).  Note the rows are at right, columns on top.  Diodes point towards the rows as PCW indicated.

The second keypad (current build) I just skipped the diodes.

I didn't use the diodes to allow double key pushes. I did it because some random "How To" article recommended it
Luckily I had enough slack in the wires to swap my row and column connectors into the 7i73. Now it works perfectly. I had to edit my HAL to transpose the matrix assignments of course.
In my case my buttons are not in a nice grid pattern, so the "rows" and "columns" are rather widely distributed.
 

RotarySMP wrote:

 I did it because some random "How To" article recommended it

 

My diodes are there because of the same article.