I own an Arachnid electronic dart board from the late 80's, and want to capture the data from the dartboard (and eliminate the manufacturer motherboard) in order to write my own custom games.
There are two components:
1) Motherboard that sends clock signal, +5v and ground to the dartboard Smart Target Interface Board (STIB)
2) Smart Target Interface Board (STIB) that collects the dart hits from a dartboard contact matrix and sends the result as serial data using one wire to motherboard after each dart hit.
The motherboard (schematic attached) is connected to the STIB via RJ11 using a 6 wire flat phone cable and I'm trying to reverse engineer the decoding of the output so I can eventually remove the motherboard and add my own Rasberry PI (or similar) so I can program my own games.
The STIB (schematic attached) uses a 76176 RS422/RS485 chip. BUT, it only uses the "A" with the "B" being NC (not connected). On the motherboard side there is no RS422/RS485 receive chip.
I own a USB to RS422/RS485 adapter, and Arduino Mega 2560 and tried wiring it up as many possible ways I can think of using UART, SPI, I2C, to monitor the serial port. Nothing intelligent / repeatable comes across. I've spent many hours on this already and I'm at a dead end.
I have a lot of programming / logic skills but minimal circuit / schematic skills and I'm willing to try whatever is suggested.
I have some questions:
1. Why no "B" wire on the transmit lines? Is one wire RS422/RS485 possible? Thought 2 wires are necessary for differential.
2. The Driver Enable / Receive Enable on the STIB are hard connected to +5, I'm guessing because they know it's the only node and will always be enabled?
3. Could this be using an RS422/485 on the STIB but reverting to something else since it's only using one wire?
4. What is the 10k resister on the motherboard pin 37 DAT1? Is that possible a terminator to fool the RS422/485 comms to somehow think there is differential?
5. I don't currently own an oscilloscope but thought of buying the Siglent SDS1104X-E 100Mhz digital oscilloscope 4 channels standard decoder. Is that a good one? Should I use an oscilloscope to further reverse engineer and see what is coming across that single data line?
What suggestion do you have for me or thoughts on this design?
Thanks so much. I've done my due diligence but I'm stuck and could use the help - thanks in advance. 😞
Jamie