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I want to make a laptop touchpad work individually with a USB adapter, but failed, on a recent Thinkpad E14 touchpad part.

Some articles on the internet said they succeeded connecting the touchpad part to PC with an USB adapter, or to SoC running PS/2 codes. Although it's rather few of the articles related.

I got a touchpad component that said from the Lenovo Thinkpad E14. The date of manufacture is labeled at year of 2017, the model number starts with 8SSM10P.

I googled a Thinkpad T470P schematics PDF, referred the touchpad as 'Click Pad'. For the pins, it illustrates (so is on the FCC connector):

1 - gnd
7 - VCC5B
8 - PAD_RESET
9 - IPDCLK, connect to PS2_CLK
10 - IPDDATA, connect to PS2_DATA

According to an article about how to detect the function of pins on a laptop touchpad, I used my multimeter. In resistance mode, The resistance between pin 1 and the back cover is zero indeed, so pin 1 must be ground; the resistance between pin 1 and pin 7 starts low and jumps and falls rapidly, so pin 7 must be the VCC as documented; the resistance of pin 8, 9 and 10 starts higher and changes slowly; other pins' resistance is rather high. As said in the schematics. With pin 1 and pin 7 wired to ground and +5V current, the voltage at pin 8, 9 and 10 was constantly at about 4.8; no voltage at pin 3; other pins' are higher than 5V. That's same as documented in the PDF schematics.

Using a PS/2 to USB adapter, and some other adapter boards, I connected the touchpad's FCC connector with 0.5mm 12 pins, to the PS/2 - USB adapter, and connected the PS/2 - USB adapter to my laptop with Win 11 installed , but it does not work. No error tip was shown in the Windows Device Manager. Tried reverting the pin 9 and 10. I've checked the wiring and the voltage of pins.

The PS/2 adapter was used for another device and works fine.

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  • \$\begingroup\$ power it and measure the current, does it seem reasonable with your assumed pinout? If so, then you might have a non-ps2-compat part; it could be bespoke to the laptop, or a custom USB interface, or even SPI or something. Try a logic analyzer and see if it can detect the signal format. \$\endgroup\$
    – dandavis
    Commented Dec 2, 2023 at 22:29
  • \$\begingroup\$ According to an article, I tested the resistance and voltage of pins. The result seems same to the pinout in schematics of T470. @dandavis \$\endgroup\$
    – sdrkyj
    Commented Dec 5, 2023 at 1:45
  • \$\begingroup\$ @sdrkyja multimeter is not a tool with which you can tell different digital buses apart \$\endgroup\$
    – Marcus Müller
    Commented Dec 5, 2023 at 6:37
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    \$\begingroup\$ My next step would be to connect an oscilloscope to the pins 9 and 10 and watch the lines while the touchpad is powered and I use it (tap, drag, ...). I would expect the typical transmissions. With a multimeter, you will not catch this. Only if I made sure that this happens, I will take the next step and connect the adapter. \$\endgroup\$
    – the busybee
    Commented Dec 5, 2023 at 7:52

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