Ergodox left hand not working

[balkamm]

Hi all,

My first keyboard project hasn't been going so well.  My friend and I soldered up all the bits and bobs of the ergodox.  When we plugged it in the right hand worked, but the left hand did not.  When we took a closer look at it, we found that the mcp23018 was on backwards.  Desoldering didn't go that well, so we had to snip a few of the connectors to remove the chip.  I ordered a new one which we installed correctly today.  However, the left hand is still not working.

At this point, we are kind of at a loss.  There were a few scratches on the board from removing the chip, but it didn't look like they damaged the tracks.

Any suggestions as to how we can diagnose what's going wrong?  Happy to provide whatever additional information is needed.  Thanks in advance.

[clickclack123]

Hi all,

My first keyboard project hasn't been going so well.  My friend and I soldered up all the bits and bobs of the ergodox.  When we plugged it in the right hand worked, but the left hand did not.  When we took a closer look at it, we found that the mcp23018 was on backwards.  Desoldering didn't go that well, so we had to snip a few of the connectors to remove the chip.  I ordered a new one which we installed correctly today.  However, the left hand is still not working.

At this point, we are kind of at a loss.  There were a few scratches on the board from removing the chip, but it didn't look like they damaged the tracks.

Any suggestions as to how we can diagnose what's going wrong?  Happy to provide whatever additional information is needed.  Thanks in advance.

What test equipment do you have? You can test the voltage on the power lines of the trrs cable just to make sure that's working. Also test the power pin on the IO Expander to make sure it's getting power. If you have an oscilloscope or logic probe you can see if the IO expander is giving any i2c data over the trrs cable.

Also make sure you got those two jumpers on the side of the trrs socket correct? If you got the IO expander in wrong, you could have also done the jumpers incorrectly. You solder them as the silkscreen on the top side. I guess if these were around the wrong way, the Ground plane would be at 5V and the 5V would be at Ground. That would not be good for the IO expander...

Maybe show us some photos of the board?

[plainbriny]

My first keyboard project hasn't been going so well.  My friend and I soldered up all the bits and bobs of the ergodox.  When we plugged it in the right hand worked, but the left hand did not.  When we took a closer look at it, we found that the mcp23018 was on backwards.  Desoldering didn't go that well, so we had to snip a few of the connectors to remove the chip.  I ordered a new one which we installed correctly today.  However, the left hand is still not working.

That's exactly what happened in my first ErgoDox!
Eventually I got a hot air gun and removed the mcp23018 (and fried it!).

As for the non-functional left hand side, I think you can try to get a multimeter. It can help determine where your left hand side is correctly connected to the right hand side, and whether the soldering in the left hand side is done properly.

[balkamm]

Thanks for the replies!  I got some help from the friendly folks at http://cambridgehackspace.com/.

The first thing we did was get out the multimeter and confirm that we are getting power on the left hand pad.  Nice clean 5v coming through there.  I also double checked the jumpers on the sides of the trrs connectors.  As far as I can tell they are correct.  I'll post pictures tomorrow.

The next thing that they had me do was follow the tracks on the pcb diagram and make sure that all of the pins that were supposed to be connected to each other are.  I think the goal was to make sure that none of the tracks had been damaged by the heat and removing the first MCP.  Once again everything was fine, buzzer on every one.

The only thing that I did find that was odd was the voltage drop across the keys.  On the right hand pad which works, there was a voltage drop of ~50mv between the two pins on each key.  On the left hand pad which doesn't, the voltage drop was ~5mv.  Not really a diagnosis, but another data point.  At that point, I also double checked the resistors and confirmed that they were the right ones.

I'll get another stab at it next week.  Someone is going to bring in an oscilloscope, and apparently they have something called a bus pirate?  We'll use that to check the output from the MCP to the teensy.

Any other thoughts or suggestions?  Did the key voltage difference sound familiar to anyone?

[Thechemist]

Can you post any pictures of the LH front and back.

[balkamm]

Here are a few shots. You'll notice that we did the connections next to the trrs connector with solder on the back side.  That's because we forgot to do them before putting on the key plate.

[Thechemist]

The second photo is kind of out of focus but from what I can see I think you need to switch your diodes around. You have them backward.

hook up the keyboard to the other side and bridge top left switch pad with the right side of the diode ( square pad side ) and let me know if the key stroke shows up.

[OldDataHands]

The second photo is kind of out of focus but from what I can see I think you need to switch your diodes around. You have them backward.

hook up the keyboard to the other side and bridge top left switch pad with the right side of the diode ( square pad side ) and let me know if the key stroke shows up.

I can't claim to tell from that blurry picture, but if your diodes
are uniformly backwards,  you should be able to fix it in firmware
by switching whether you scan rows or columns.

[balkamm]

Here's a closer more focused closeup.  Are the diodes supposed to be opposite on opposite boards?  I guess that might make sense.  I'll try the software fix and see if that helps.

[Thechemist]

Here's a closer more focused closeup.  Are the diodes supposed to be opposite on opposite boards?  I guess that might make sense.  I'll try the software fix and see if that helps.

Not sure how easy the software will be ( because of the split design with I/O expander ) but the diodes are for sure placed the wrong way consistently across the board that I do see in the picture witch would explain why that side is getting 5v but isn't working.

[balkamm]

I'm going to try compiling this: https://github.com/benblazak/ergodox-firmware

Apparently I can change the way that it scans here: https://github.com/benblazak/ergodox-firmware/blob/master/src/keyboard/ergodox/options.h

[balkamm]

Oh yeah, and thanks!  I'm pretty sure that's the problem, and confident I can fix it!  Thanks everyone!