I'm trying to connect an old Omron thermal printer (PRT-1 Z, companion of the 705CP Blood Pressure Monitor) to a Raspberry Pi Pico. The idea is being able to print something using the Pico. The printer doesn't have a standard connector and instead has a proprietary mini-USB-like male connector.
What have I tried so far:
I tried disassembling the printer to have a look at the PCB. I notice the cable pinout is labelled "USB". Unfortunately, each wire is only labelled with its color (BK, R, etc.) and not with its function. I assumed it was the standard wiring (BK for GND, R for V+, WH for D- and G for D+), and tried wiring it to my Pico (black to pin 3, red to 40, white and green to GPIOs 15 & 16).
I naively tried to send random data to the printer to see if something happened. Nothing did.
Then, I tried to see if I had an incoming signal while pressing the buttons on the printer, which has 4 buttons (feed, to control paper feed; graph; all data; data/stop). The program I used to do so (MicroPython through Rshell & REPL) is the following:
from machine import Pin d1 = Pin(15, Pin.IN) while True: print(d1.value())
All I got was only a continuous series of 1 while the LED on the printer was blinking.
Any advice on how could I proceed to establish connection with this printer?
Edit: thanks to @jsotola's comment, I realized I first needed to identify the correct USB pinout. I opened a separate question on the Electrical Engineering Stack Exchange.