Let's first start of by explaining that I do not have a decent background in electronics and interfacing with them, so maybe this is a stupid question. I am currently trying to connect an old Harvard 33 syringe pump (website, PDF manual) to a computer, with the goal of controlling things like pump rates and direction. For this purpose, I connected the instrument to my computer using a D-sub/USB conversion dongle. I then connected to the dongle with PySerial without issues. However, whenever I try to send commands or request the instrument's output, for example
write("RUN\r"), the instrument does not do anything at all. Requesting data (
read(100)) returns only a couple of
\x00. I suspect I am communicating with the dongle itself rather than the pump. When the pump is turned off or unplugged, I get exactly the same results!
Could anyone explain to me why my method does not work?
My Python code for reference:
import serial # PySerial module # open the connection ser = serial.Serial("/dev/ttyUSB0", baudrate=9600, bytesize=8, stopbits=2, timeout=1) print ser # returns [Serial<id=0x1cc7610, open=True>(port='/dev/ttyUSB0', baudrate=9600, bytesize=8, parity='N', stopbits=2, timeout=1, xonxoff=False, rtscts=False, dsrdtr=False)] # see if the connection is truly open print ser.isOpen() # prints True # run the pump motor ser.write("RUN\r")
Additional observations: when the instrument is plugged in but the above code is not running, the pump does all sorts of things at random (move one way, stop, move the other way, etc.). This behaviour is much less pronounced but still present when the code runs (and 'locks' the channel or something?). This seems to suggest that the reference voltages (logical high and low) are not properly set at 2-5V and 0-0.5V respectively