Mayfly Dissolved Oxygen Sensor

You might want to check out Atlas Scientific DO sensors (https://www.atlas-scientific.com/product_pages/kits/do_kit.html). They are galvanic probes that are cheap and fairly accurate (+- 0.05 mg/l), but they do require a fair bit of effort to piece together. You would need the DO kit (previous link, $280), an isolated carrier board ($40, https://www.atlas-scientific.com/product_pages/components/single_carrier_iso.html), and an extension cable where the connection to the probe needs to be waterproofed with CoaxSeal ($17,https://www.atlas-scientific.com/product_pages/components/bnc_10.html). You then would need to figure out how to connect the carrier board to the Mayfly. We are starting to use them for our project, and we’ve created our own carrier board to hold 3 sensor chips rather than use their carrier boards (https://github.com/acgold/Atlas-Scientific-Carrier-Board). They work with the ModularSensors library (in I2C mode), and the data sheets from Atlas Scientific are great (https://www.atlas-scientific.com/_files/_datasheets/_circuit/DO_EZO_Datasheet.pdf?)

Based on the list of supported sensors (https://github.com/EnviroDIY/ModularSensors), it looks like a Yosemitech DO sensor is another option.

I highly recommend the YosemiTech DO sensors, which use optical sensing technology for long-term stability. https://www.yosemitech.com/en/product-cat-11.html

They use Modbus communication and can be user-calibrated. Here are their two main models (the Y505 is new and not on their website).

Y504 (standard model):

~$650 each (plus shipping plus 25% new China import tax)
±1%​ DO accuracy
±0.2°C temp accuracy
5 m standard cable length (10 m at additional cost)
10 s response time

Y505 (low-cost, aquaculture model):

~$450 each (plus shipping plus 25% new China import tax)
±3%​ DO accuracy
±0.5°C temp accuracy
10 m standard cable length
40 s response time
no protection cap over sensor surface

For more info, see https://github.com/EnviroDIY/YosemitechModbus/blob/master/doc/Y50X-DO-ProductProfile.pdf

There are a few minor drawbacks to YosemiTech. They require purchasing with a bank transfer rather than a credit card, and their documentation isn’t great. However, we’re trying to help them with the later by reposting manuals and other info at https://github.com/EnviroDIY/YosemitechModbus. Overall, however, I find their sensors to be of excellent quality, and their email response time to questions (and also a warranty repair) have been quite good.

I forgot to mention that YosemiTech also makes a multi-parameter sonde with an optional wiper. http://www.yosemitech.com/en/product-20.html

This is an approach to having a wiper on the DO probe, as none of the stand-alone DO probes have a wiper (unlike Turbidity, Chlorophyl and Blue-Green Algal stand-alone sensors, which have models with built-in brushes).

Also, as with all YosemiTech sensors, you need to power the DO sensors with 6-12 V (5V only works if you have in-line capacitors and no brushes) and you need an RS485-to-TTL serial converter. See https://github.com/EnviroDIY/YosemitechModbus#suggested-setup-with-an-envirodiy-mayfly and https://github.com/EnviroDIY/SensorModbusMaster/tree/master/hardware/Modbus-Mayfly_WingShield for details on that.

The status of the communication between the Yosemitech’s and the Mayfly hasn’t changed since May.

The library for communicating with the Yosemitech’s is here: https://github.com/EnviroDIY/YosemitechModbus

It depends on the SensorModbusMaster library here: https://github.com/EnviroDIY/SensorModbusMaster

If you want to use the Yosemitech in combination with a OBS3+ and log the data, you can use the ModularSensors library here that supports both: https://github.com/EnviroDIY/ModularSensors