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Connector for trackpad working

A project log for thumbMouse

Finger-mounted bluetooth pointer device, based on BlackBerry trackpad, for avoiding shoulder/wrist pain from mouse/laptop touchpad use

Matias N.Matias N. 05/27/2020 at 19:504 Comments

Today I received Mouser order containing necessary components for building the current design of the thumbmouse prototype (based on BlackBerry 9900 trackpad). This trackpad has a thirteen contact FPC with 0.3mm pitch (tiny!). It is supposed to have same functionality as the 9800 (also thirteen contacts but with a more workable 0.4 mm pitch) but I could not find a suitable connector for it. On Mouser I found one connector that was supposed to be compatible with the 9900 so I targeted this version for starting.

Some time after ordering I realized from the connector datasheet that due to the shape of the FPC  it wasn't an exact match for the connector so I realized I would have to modify it (not ideal). Today I finally got the test the compatibility. I had to cut the side lips of the FPC which would not let me insert it fully. You can see the surgery I had to perform in the following video (using a nail clipper):

This allowed me to insert it correctly but I had to be sure that the FPC mated correctly with the connector's contacts. I checked continuity using the microscope and everything seemed to be OK! (no sound from the microscope, but believe me it beeped as expected). It is incredibly how fragile the connector is, after pressing the tester leads against it made a bunch of bumps.

So, with this I'm now fairly confident this should work. I'm now waiting for the PCBs and BLE module which should arrive this week. Finally I need to get the passives and SOIC clamp in order to flash/debug the board using the SOICbite connector I included in the board.

While waiting for all things to arrive I actually started designing another version of thumbmouse targeting the 8520 series of trackpads which use a more standard connector which would not require any adaptation. I will continue to iterate this version with everything I learn from this.

Discussions

Matias N. wrote 05/27/2020 at 20:56 point

Ah, I understand. Note that the trackpad is not capacitive though, but optical (just like an optical mouse) which makes it really precise for its surface area.

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Simon Merrett wrote 05/27/2020 at 20:06 point

Well done! I keep thinking about an ATtiny 1 series using the peripheral touch controller on a small flex PCB as a slide control moulded into a keyboard cap. I think it would be fun to add "physics" like the way your phone screen carries on scrolling for more or less "distance" when your finger lifts off it, depending on how fast you swipe. 

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Matias N. wrote 05/27/2020 at 20:18 point

Not sure if I fully understand your idea, but something similar using a trackpad was done for the Corne Keyboard: https://github.com/vlukash/corne-trackpad/

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Simon Merrett wrote 05/27/2020 at 20:33 point

Yes, similar but much smaller overall. The PCB with the microcontroller would have the capacitive pads so the separate trackpad component wouldn't be necessary. I think you could fit it in a 2u key cap. 

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