Incompatible Widget error


I have a Raspberry pi 3b that is working as “fish tank controller” with pH and EC/TDS probes connected.
With a python script I send pH and EC/TDS data to a Cayenne dashboards through MQTT.
Everything works, there are 3 gauges with pH, EC and TDS (TDS are calculated via software as EC multiplied by 0.64) and 2 line charts, respectively with pH and EC graph.
Now I would like to add TDS values to the same chart of EC so I clicked on “Settings–>Add Data Point” then “Graph Settings box” appears, I select the device “TDS” in the list and the error “Incompatible Widget” appears.
I can’t figure out why that error appears…TDS is simply the value of “EC multiplied by 0.64” (and rounded to integer value) calculated in the python script and sent through MQTT like EC and pH are.
Where is my mistake?
Thank you, regards.


Have you used a separate channel for each widget?

Yes, both gauges (EC and TDS) are set with the same range (0-1000).

i mean the MQTT channel. can you share the code you are using.

These are the lines where I send the values to Cayenne:

client.virtualWrite(6, 0+ec_valore, dataType=’’, dataUnit=’’) <— this is the EC value (=0+ec_valore)
tds_valore= int(ec_valore*0.64)
client.virtualWrite(7, 0+tds_valore, dataType=’’, dataUnit=’’) <— this is the TDS value (=0+tds_valore)

6 is the assigned channel to EC probe, 7 the one for the TDS value.

in total, you have 5 widgets and are you using 5 different channels?

No, I have 3 gauges set on channels 4, 6, 7 (respectively pH, EC, TDS) and 2 line charts “mapped” to channel 4,6 and I would like to add channel 7 to the line chart #2 (where I already have channel 6).

this is what i am trying to tell, you need to have a different channel for each widget.

tds_valore= int(ec_valore*0.64)
client.virtualWrite(7, 0+tds_valore, dataType=’’, dataUnit=’’) —>gauge widget
client.virtualWrite(7, 0+tds_valore, dataType=’’, dataUnit=’’) ----> line chart

Ok but how if I want 2 devices data on the same widget “line chart”?
I already did it with another raspberry connected to a SDM120C to monitor electical consumption of my house.
Also this raspberry sends data to Cayenne and I have a line chart where Voltage and Power are displayed with different colors but in the same widget, of course power and voltage have two different channels like EC and TDS.

you can select the different device in the dropdown.