Panther Logger 9: Read a YSI EXO Sonde with RS232

The YSI EXO instrument is a multi-parameter data sonde that is an industry standard in aquatic monitoring programs. The Panther Logger can power and read this instrument in long term deployments, such as on a data buoy or a fixed monitoring station over a river. In this tutorial we show how to wire up the EXO2 sonde with the Panther Logger and program the Panther Logger to request, receive and parse serial data from the EXO2 using the Panther Logger's RS232 serial interface. 

In order to read the EXO2 sonde with the Panther Logger you will need the following:

1.     EXO2 Sonde with cable
2.     DCP Adapter
3.     24 - 26 AWG hookup wire of various colors (stranded)
4.     Panther Logger Board
5.     Battery or power supply set to 3.7 to 4.2V

The EXO2 sonde does not output RS232 signals by itself. To do this, YSI sells their customers a device called a DCP Adapter which translates YSI's proprietary signal into RS232 and SDI12. Use of this adapter is discussed in the EXO2 manual (link here). Note that the EXO3 sonde has integrated SDI12 output. As such it would make more sense to read an EXO3 sonde with the Panther Logger using SDI12 since the DCP adapter would not be needed. 

The EXO sonde requires that we send it RS232 commands (page 38 of the EXO manual). These commands can be used to activate the sonde's wiper, wait for the dissolved oxygen sensor to warm up, change baud rates and request data among a few other tasks. Commands must end with a carriage return (i.e. "/r").

Go to our Github page for the "ReadEXO_RS232" script here. Copy and paste into a new script in the Arduino IDE and save it. This script powers on the EXO with the switched 12VS rail of the Panther Logger, then waits for it to startup and complete one wipe of the sensors, then requests data with the command "data/r" , reads it back and then parses that data into individual float values. The script then turns off the 12VS switched rail and the EXO sonde powers down. After a delay of 10 seconds the loop repeats. 

The data/r command returns a comma separated string of values. This string of values is defined in the sonde. To identify this string of values it is necessary to connect the sonde to a PC using the YSI USB adapter for EXO sondes and the KOR EXO software.  In the deployment section of the software the order of sensor output variables can be chosen.

With the DCP adaptor and EXO sonde hooked up to the Panther Logger, attach the USB cable to the Panther Logger board to power it and to your computer. Plug in the battery if available. Upload the ReadEXO_RS232 script to the Panther Logger board and open the serial monitor. You will see the serial monitor report when it is turning on th EXO and waiting for it to complete a wipe of its sensors. At the same time you should see the blue and red LEDs on the sonde turn on. The LED on the DCP adaptor will turn on solid for several seconds and then turn off. After about 20 seconds the DCP adaptor LED will start to blink and then data will be requested by the Panther Logger, which will show up in the serial monitor.

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