I have a trackpoint from a thinkpad keyboard with a trackpoint mounting a PTPM754DR microcontroller, what I'm trying to do is to find the usage of various pin on the trackpoint board and connect them to a teensy 2.0 that already controls a keyboard (I'm using this firmware https://github.com/tmk/tmk_keyboard), what I've found on various sites and forums like geekhack are info from other trackpoints with a different pinout, I say so because I've traced at least the mouse buttons and saw the vcc and ground that have bigger traces than the others, how can I find the purpose of other pins? I cannot connect that keyboard back to a laptop.

Here is some images of the trackpoint and what I was able, probably, to trace

enter image description here enter image description here


1 Answer 1


According to this post on the geekhack forum:

R61 trackpoint pinout (with PTPM754DR) « Reply #20 on: Wed, 23 January 2013, 08:04:09 »

  1. DATA
  2. RST
  3. BTN1
  4. BTN2
  5. BTN3
  6. CLOCK
  7. GND
  8. VCC

When connecting to PS/2 interface, DATA and CLK should be pulled up to vcc using 4k7 resistor, RST to GND using 100k resistor and RST to vcc using 2.2uF capacitor.

enter image description here

Notice the boards look identical. Also this other post and another:

enter image description here

That last post has everything you need for using your trackpoint on the TMK firmware too.

  • \$\begingroup\$ I saw both of those posts but does this mean I got my tracing wrong? (notice the mouse pinout I was able to trace with a tester) I don't want to fry the teensy by connecting wrong pins, is there a precaution I can take in this regard? \$\endgroup\$
    – araif
    Commented Feb 17, 2015 at 18:11
  • \$\begingroup\$ @araif your traced mouse buttons match theirs. 3rd, 4th, 5th traces, starting from the bottom. Your board has a trace that looks empty, ignore that one, and start counting from the first trace the cable is wired to. \$\endgroup\$
    – Passerby
    Commented Feb 17, 2015 at 18:22
  • \$\begingroup\$ yes but I have btn2 and btn1 inverted, I tested that different time and I'm pretty sure is not a mistake, but I'll retry later this evening. \$\endgroup\$
    – araif
    Commented Feb 17, 2015 at 18:28
  • \$\begingroup\$ @araif the buttons are arbitrary. A switch is a switch, doesn't matter if you call it btn1 or btn2. \$\endgroup\$
    – Passerby
    Commented Feb 17, 2015 at 18:29
  • 1
    \$\begingroup\$ @araif these boards are so similar, there is no reason to expect that. And even then, these are all outputs except for clk. And ps/2 is an open drain protocol. The pull up resistor does the work. You'll be fine. \$\endgroup\$
    – Passerby
    Commented Feb 17, 2015 at 18:49

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