Hi
Busy building a pH controller, the "monitor" side of think works fine and its reading pH connectly, it has a output of 1V per Ph. I've taken the that voltage through a 10K resister to the input of the "switching opamp" (LM358), which it acts as a comparator against a reference voltage, the output from this drives a 2N2222 transistor which in turn drives a relay.
THE PROBLEM
Because the input signal changes very slowly, when its at the threshold point of the opamp (against the Ref Voltage) it start to form a "square Wave" output and causing the relay to "vibrate", and not acting as a "clean" switch.
Attched is a basic schematic of the comparator and relay driver.
Thanks in advance.