I am currently working on a project where I need to simulate a pH probe's output voltage. For those that don't know, a pH probe uses pH-sensitive materials and fluids to output a voltage. The output voltage varies based on the hydrogen concentration of the solution the probe is measuring. The probe is hooked up to a pH meter, which is in essence just a multimeter, and the small voltage value is then converted into a pH value. A basic breakdown of this conversion is as follows:
pH Value | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | Probe output (in mV) | 237 | 177 | 118 | 59 | 0 | -59 | -118| -177 | -237 |
To sum up very briefly, values below 7 pH cause the probe to output a positive voltage. Values above 7 pH cause the probe to output a negative voltage. Values of 7 pH exactly cause the probe to output no voltage.
Basically, I need my Raspberry Pi to be able to output voltages in this range. The goal is that the RPi can then be hooked up to any standard pH meter via BNC. The Pi would then output a voltage similar to the ones described above, and the pH meter would believe a real pH probe was attached, and display the pH that corresponds with the voltage the Pi is generating.
I am rather new to "making" and electronics in general. I have done some research and it appears that I will need a DAC to convert the Pi's digital output to an analog voltage. What complicates things is that I would need to output a negative voltage for values above 7 pH. Since the scale appears to be linear, I may be able to simply output the proper mV, then flip the voltage if the values are over 7 pH. I don't know how easy or feasible this is, however.
As I mentioned, I really am sort of lost at where to start. If anyone could give me some advice as to where to begin reading, or some chips/tutorials that may be useful to learn how to accomplish my goal, I would be grateful. Thank you!