My sensor (photodetector + LED) communicates (send-only: does not receive) via RS-232 at 9600 8-N-1. It has 4 lines for

  • power
  • ground
  • RS-232
  • TTL Serial

The sensor's ground and RS-232 are connected to a Manhattan Serial to USB cable.: Is there any reason why this would not work? or is there anything else to be done / considered?

Battery power has been applied and seems to power the sensor's LED (LED is bright). Raspberry pi has been configured per

The rPi serial-to-usb adapter has been tested as described (click) here The sensor was plugged in: is it reasonable (or have I missed a step?) to expect that:

cat /dev/ttyUSB0

will display the raw data sent by the sensor? Is there a better (surefire+easy) to confirm that serial data is streaming from the sensor? Thank you for actionable suggestions (executable commands).

  • 1
    You say it has been tested. Did it work? What is the output? cat is a poor choice - it depends what the sensor outputs. I would use a terminal program e.g. minicom. Incidentally if you have a ttl output why not connect to the Pi RxD (via a divider to ensure voltage does not exceed 3.3V).
    – Milliways
    Commented Jan 26, 2016 at 7:04
  • 1
    What sensor? Are you sure it uses RS232 (+/- 12V) rather than serial TTL (0-5V)?.
    – joan
    Commented Jan 26, 2016 at 8:32
  • @Milliways: No, in the sense that I do not see inbound data from the sensor. I need to perform a loopback tests starting from the Manhattan device to verify that it is not the problem (isolate the problem[s]). Sensor outputs both 5V TTL and RS-232: RS232 was selected for ease of physical connectivity, however, bridging 5V-TTL with a voltage divider is looking more and more attractive.
    – gatorback
    Commented Jan 29, 2016 at 17:48
  • @joan: good questions :) A sophisticated Photo diode cricuit outputs both 5V TTL and RS-232. The data sheet does not provide RS-232 voltage levels.
    – gatorback
    Commented Jan 29, 2016 at 17:50

1 Answer 1


I usually use screen /dev/ttyUSB0 9600 to ensure I get exactly what I expect at the correct speed. You may have to apt-get install screen to make that work.

I don't see any issue with what you are doing assuming you got the TX/RX parts right and didn't accidentally cross the RS-232 signal levels onto something TTL level. Note also your TTL serial could be 5 V, which could hurt things if connected directly to 3v3 logic.

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