pH probes / monitoring

Has anyone connected a pH probe to their Pioreactor?

Raspberry Pi compatible pH boards seem to be available from Atlas Scientific, Anyleaf, Homelab-pH, DF Robot and others. The Atlas Scientific seems to be mentioned most in my brief googling.

I guess integrating one of these may be a step harder than the average plug-in, as a calibration interface would be required.

1 Like

nanocastro on the GOSH Forum has confirmed that IO Rodeo’s pH FeatherWing is fully open source, as are their two pHMetros. Assuming we can get the same accuracy out of these and a standard probe as we can with one of the closed source options above (at least I couldn’t see evidence that the 4 linked in my earlier post are open) I’d be more inclined to buy one of them first.

Since it’s open, there appears to be good documentation in English and there are hardware calibration buttons that I assume may remove potential plug-in complexity, I’ll order a pH FeatherWing, unless anyone pipes up soon to say they’ve already had success with another route.

Do you think we would actually need the Adafruit Feather for it, or could we have it all running on the Pioreactor’s Raspberry Pi? I’ll ask Jo & William on the GOSH forum too, since they appear to be its creators…

I haven’t researched much about what pH probes will work with the Pioreactor. Mostly I’ve said to others: “pH probes are too large to fit into the vial”, which is mostly true, but there do (1) . exist (2) micro probes of 6-8mm diameter that would fit.

Also note that I am assuming the use of the Vial Cap A design, which has a large port (g1/8 threaded, 8.6mm diameter) for additional sensors.

Finding an open-source pH probe that could fit this size may be the biggest challenge. Calibration routines, jobs, and charts can be created pretty easily with the software.

You could re-design the cap to accommodate a large probe, but that’s additional design work!

I haven’t actually found any Open Source pH probes, and I don’t imagine I will as I assume the probes take so much precision engineering that the community would struggle to build them anyway.

I am however now in discussion with the makers of the pH FeatherWing which is a board with a standard BNC connector that should accept the majority of commercially available probes, including the 6mm Cole Palmer one that I found via your 2nd link.

Hi Martin

Did you find a good solution for a pH probe?
We are looking into that as well. What did you test and what solution did you go with in the end?


Hi Martin

I found that the pH FeatherWing wasn’t appropriate for use with Raspberry Pi, as its output is analogue. I didn’t find another open source option, so haven’t purchased anything so far.

Kind regards


Normally a Raspberry Pi can’t read analog signals. However the Pioreactor HAT has a StemmaQT connector, which means you can attach ADC (analog-to-digital-converters) like this one. This ADS1015 board can be used to convert analog pH signals to digital values and read over i2c.

This pH featherwing still needs a µc to control it though, so that µc could have both ADC + StemmaQT.

Another option use the µc to read pH signals, convert to digital, and send them to the Pioreactor over MQTT. This requires the µc to have a wifi connection and network creds.

1 Like

Hi Cam,

any news on pH measurement solutions? I am scaling up the Pioreactor and designed a GL45 bottle cap with several ports and the space for a 5 mm stirring rod.
I want to add an opening for a pH probe, but basically it can’t have a diameter of more than 8.6 mm. Do you know of any one that can fit?


No solution has emerged yet unfortunately. It’s one of the most common asks, so we are actively thinking about it!

Hm, I just found this probe: Orion™ Economy Series pH Combination Electrodes

The diameter is 6mm, which I believe would fit into the vial cap A’s port, and the price is reasonable (I know I know). It has a BNC connector, and can integrate with the EZO pH system¹:

I’m currently writing some software to incorporate the latter into the Pioreactor: [wip] Integrating pH / DO probes (software only) · Issue #483 · Pioreactor/pioreactor · GitHub

This came from this paper:

¹I’m kinda confused about the connector though. The probe has a BNC connector, while the EZO has an SMA connector. I think you need a BNC to SMA connector.

I bought a DF Robot Gravity V2 set and Gravity: I2C ADS1115 after being told on the GOSH Forum that Atlas were way too expensive. I believe the DF Robot units are open source, they use BNC connectors (and come with a regular probe) so I’d be tempted to try one of them before investing too much time into the EZO software. If pH became a standard ask, you could presumably integrate the I2C into their BNC board for a single board Pioreactor pH expansion.

I was always planning on posting here about it, but thought that testing it would be just around the corner. I’d be happy to try one of the Orion’s, once we have funding & can figure out how to fit it plus two electrodes and a sparging tube into a Pioreactor. Otherwise I’ve been looking into flow-cells so we can just measure pH in our outlet.