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I'm trying to figure out how an OMRON Printer HEM PRT 1-Z operates (see related question on the Raspberry Pi StackExchange & IC identification question) in order to wire it to a Raspberry Pi Pico. Since I couldn't find any "service manual" or schematics diagram online, I'm having a look at the PCB and I'm trying to understand the underlying schematics.

The printer doesn't have a standard connector and instead has a proprietary mini-USB-like male connector. The PCB indeed has the cable pinout labelled "USB", but the main microcontroller unit (TMP86CM29B) doesn't have USB support. The printer head is a SII MTP102-16B.

Here are some shots of the PCB: enter image description here

Any insight on the USB pinout? How can I proceed to find out? How come the cable is labelled "USB" if the MCU doesn't support USB?

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  • \$\begingroup\$ Well why do you think it is USB? I don't see why they would use something so complex like USB just for printing blood pressure data. Measure the pins with a multimeter. The wire colouring does match USB so they might have just used an existing proprietary miniature connector that pocket cameras of the era have used for USB but for non-USB purposes. Also the images are so blurry it is impossible to see where the "USB" connector connections go. \$\endgroup\$
    – Justme
    Commented Jan 2, 2022 at 13:30
  • \$\begingroup\$ Yeah, this makes sense. Sorry for the bad shots, I don't really have a quality camera at hand & the PCB is quite small. I thought it was USB because the PCB reads "USB" where the wires are soldered \$\endgroup\$
    – corbin-c
    Commented Jan 2, 2022 at 13:44

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Most likely, it follows the standard USB cable coloring and also USB connector pinout.

Like this (From Wikipedia)
USB Pinout

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  • \$\begingroup\$ Thanks. Yet I've been told « there is no standard color coding of USB cable wires »... How could I be sure of the pinout? What about the fact that the MCU doesn't has USB? \$\endgroup\$
    – corbin-c
    Commented Jan 2, 2022 at 13:26
  • \$\begingroup\$ It'd be very unlikely for black not to be ground and red not to be Vbus. As long as those are correct, there is at least no risk of breaking anything. Swapping D+ with D- will not work, but nothing will break. So if it doesn't work, just swap green and white. \$\endgroup\$
    – Klas-Kenny
    Commented Jan 2, 2022 at 13:31
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    \$\begingroup\$ There is a colouring defined in the standard. Another thing is if cable makers actually care about the colouring, as it can't be seen by anyone. And most likely the printer has no USB, just a custom link cable. I suggest to not to try to blindly connect it to any USB device such as PC as it may damage the PC or the printer. Test first with a multimeter. \$\endgroup\$
    – Justme
    Commented Jan 2, 2022 at 13:41
  • \$\begingroup\$ @corbin-c I saw in your RPi-question that you tried wiring it up like my suggestion and tried sending random data to it. Did the get enumerated on USB? Can you see the printer with for example lsusb on the Pi? If so, it's wired correctly. \$\endgroup\$
    – Klas-Kenny
    Commented Jan 2, 2022 at 13:44
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    \$\begingroup\$ @corbin-c Oh, right. I'd start by tracing the two middle traces on the PCB, to find where they go on the board. That might give you a clue about what's going on. \$\endgroup\$
    – Klas-Kenny
    Commented Jan 2, 2022 at 13:53

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