Liquid Level Sensor, TL-136 in combination with shelly plus add-on

MarcoL · Sep 18th 2023

Hi All,

I am looking to purchase a TL-136 water presure sensor (link below) to measure the depth of my rain water tank and was hoping to connect it to the shelly plus 2 with Add-On
The sensor requires 12-32 volts but i dont think the add-on has this and should require an external 24v power supply.

what ports would i use and how do i connect this?

Sensor:

Liquid Level Sensor, TL-136 Liquid Level Sensor Water Level Sensor Detector 12-32VDC 4-20mA Signal Output(Measuring Range 0-1m) : Amazon.nl: Business, Industry & Science

Hope someone can help

Thanks!

thgoebel · Sep 19th 2023

Welcome to the forum!

Yes, indeed - you’ll need a separate power supply delivering 24V DC. Because you want to determine the liquid level in small steps, you’ll have to use the analogue voltage measuring input of the Add-On (ADC). Plus a resistor of 500 Ohms (generally two 1kΩ 1% in parallel). This resistor gives a voltage from the signal current (4 to 20mA gives 2 to 10V). Unfortunately, you’ll have an offset of 2V due to the base current of 4mA, which is used to indicate malfunction of the sensor (e.g. a breakage of the sensor wires or other things). Ground level of power supply, Add-On pin GND and sensor GND has to be connected each other.

You’ll find a lot of threads with the subject “4-20mA” as key word in a search in the forum. Due to the fact, mostly all threads are in German language, you’ll need presumably a translator…

thgoebel · Sep 19th 2023

Olsche has traced a sketch as a hint for the wiring of the components:

Many thanks to Tobias!

MarcoL · Wednesday, 4:09 pm

Hello thgoebel,

Thanks so much for this info. Ill get right on it. The sketch in your second post gives an access denied however. Would love to have an example sketch. If you could post this again, that would be wonderfully.

Thanks,

Marco