Objective: interface to an HPLC pump via the RS-232 interface described in the manual. Communication protocol is well described. Pinout is not described at all. Can I guess the pinout based on voltages?
Information: I have a LKB Bromma 2150 pump, and am trying to use an Arduino to control it. The manual states that it has the following RS-232 parameters, and has an entire page of simple enough commands.
I have numbered the pins on the 6-pin connector in the following way, and by measuring their pair-wise voltages, was able to figure out the voltage of each pin while the device is on but not communicating.
The voltages are as follows:
- Pin 3 (4.93V)
- Pin 1 (1.26V)
- Pin 2 (0.04V)
- Pin 4 (0.00V)
- Pin 5 (0.00V)
What I need help with: does someone with more RS-232 experience think they can guess which pins are what? I am assuming its a 5-wire RS-232 protocol with gnd, tx, rx, cts, and rts. I really only need to determine the gnd, tx, and rx.
Note: the Arduino is communicating through a Sparkfun Level-Shifter designed for RS-232 communications--no need to worry about blowing up the Arduino.
Additional Information: the instrument has a BNC connector that goes to a chart recorder. The ground on this connector is shorted with Pin 5 on my diagram.
Another commenter also pointed out that the manual states the communication protocol is RS-232C.
Update (15 AUG 2016): Still messing around with this pump, but haven't been able to get it to work yet. Switched to a MAX232 based TTL logic shifter, and that got another piece of instrumentation going, but this pump is still a puzzle.
Update (16 AUG 2016): Scope in hand, still trying to figure it out. Using PIN 5 as ground and PIN 2 as probe, I see that PIN 2 appears to be a 0-5 VDC signal going high only when the pump is in "Run" mode. Having trouble figuring out how to prompt the pump to send data over the Tx line (whichever pin that is) that I can detect with my scope.
Update (16 AUG 2016 Later): I think I've got it. This pump can be operated in standalone mode, or using a LKB Bromma 2152 controller. I found the manual for the next generation controller (LKB Bromma 2252), and it gives a pinout for the connections to the "LKB Bromma 2250" pump. Uses a 6-pin connector with a NC pin for control, and a 6-pin connector with 2 NC pins for the 'recorder' leading me to believe the pinouts are the same.
Further, the manual states that the LKB Bromma 2252 controller is compatible with my LKB Bromma 2150 pump--meaning the connection has to be the same. The confusing bit is that the pin labeled "PULSE"--what I had thought was ground--would be tied to the ground of the BNC connector. Strange.