REV10 listening in on two devices talking 232 voltage levels

Just received the new REV10 and powered it up.

I have never used a bus pirate, so I want to know if two devices are talking 232 voltage levels, not ttl, can i probe one line to see if any communication is flowing over the wire?

From what I can obtain the bus pirate can only go up to 5V so my assumption is I’ll kill the REV10 board if I hook it up directly. What can I do?

Connecting to RS232 levels probably won’t kill the Bus Pirate, but this isn’t guaranteed. Also you won’t be able to send data with RS232 levels.

You should put a RS232 transceiver between the Bus Pirate and your RS232 devices. For example a MAX3232 or any of it’s many clones. There are also breakout adapters with one of these available for cheap.

Thanks @electronic_eel

I did further reading and can confirm the levels are only up to max of 5V, so yes I’ll get a transceiver to do voltage conversion.

I was hoping someone have done this using either a transceiver like option to confirm it’s possible to achieve sniffing the traffic on the bus that already connects two existing devices.

Sniffing a serial bus is generally no problem. The Bus Pirate has two UARTs so it is also possible to do a two-way man in the middle type logging thing if it would be useful.

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@ian , that is a great suggestion, I’ll go scratch around in the code to see if I can find something. My biggest need is to see if the voltage levels do change as data is transmitted over the wire between the two original devices, without intervering with the wiring itself. I have device A and B that is supposed to talk to one another, but device B is not answering. When I change device A with my PC for example, B starts answering. When I plug my PC into A, I can see data begin transmitted. When I capture the data stream, and replay it from my PC to B, the unit answers. This is all on the same BAUD of 9600.

My challenge is without a profesional osciloscope to have a way to measure the RS232 voltage levels between A and B. I would need to convert a -16 to 16V peak to peak signal, into a 0-5V signal, so that I can view the voltages without disconnecting the original two devices, or alternatively I’ll just clamp the negative voltages to 0.

You could tap the signals after one of the device’s RS232 buffer. They’re usually SOP chips, I think, so pretty big leads.

Thank you, it worked as suggested. I used a level converter between the Bus Pirate RX pin and the RS232 line as it is Hi-Z and should not affect the line. Can “see” the data over the line depending which one I chose A>B or B>A?

I’m glad you got it going so quickly. What kind of buffer did you use?