Considering 8 Relay I2C board and 4-20 mA board

I have two questions in possible using an 8 relay board and 4-20 ma board with a Particle Photon:

I am looking at your I2C 8 Relay board and are considering it for use. My first question is, what sort of isolation does it have to protect the low side from high voltages, say putting 120/240 VAC on one relay and it experiences a fault? Optoisolators or magnetic protection?

I have a load of Rosemount pressure and temperature transmitters using 4-20 mA, which require 24 volts of power. My plan is to provide 24 VDC with a dedicated industrial power supply in series with 4 devices. What would be the correct board to receive these 4 inputs and how would they be wired to utilize the single power supply?


Our current relay controllers in that series do not offer optical isolation on mechanical relays. They are however used for switching 120/240VAC regularly and are completely fine if the loads are resistive and not inductive.

If you require optical isolation for your application then I would recommend solid state relays such as this product:

We use high quality Crydom solid state relays and they are ideal for almost any switching application as long as the load meets the minimum current draw requirements of the relay(60 mA).

Would you care to answer the question on wiring in the Rosemount Pressure and Temperature transmitters?

are the 4-20mA sensors 2 wire sensors ?

Yes they are two wire devices.

What is the max amp rating for the solid state relays? I’m looking for at least 20 amps.

You can use this board

This board has one board power supply( 16V) so you wont need any external power as well.

Most of these 4-20mA sensors works at 9-24V DC.

Depending on loading of the circuit, 16 volts may not be enough to maintain above liftoff for the devices and is close to the minimum operating range. What board would you recommend with an external power supply?

In 4-20mA system the max load could be 20mA. The on board power supply is designed to provide 16VDC@20mA.
The load resistance of the 4-20mA receiver is 4.99Ohm.


You can take a look at all the different solid state relays we offer here:

I will check it out, Thank you for the quick response!

I have the board and using the I2C scanning code, I can see the 4-Channel 4-20 mA Current Loop Receiver 16-Bit ADS1115 I2C Mini Module at address 73n. What would be the best way to pull data back from 1-4 4-20 mA transmitters? I’m new to the code, but I can only finds stuff for ads1118 for arduino, while I’m trying to pull it in through the Particle Photon.

Thank you,

you can find arduino lib over here

and particle lib over here

Let me know if you have any other questions.


So I have copied the particle library (.h and .cpp) files and used the example to try to read data from the inputs. When I try to compile, I get the following errors:

ads1115.ino:9:0: undefined reference to "ADS1115::setAddress(int)"
ads1115.ino:15:0: undefined reference to "ADS1115::readInput(int)"
ads1115.ino:21:0: undefined reference to "ADS1115::readInput(int)"
ads1115.ino:27:0: undefined reference to "ADS1115::readInput(int)"
ads1115.ino:33:0: undefined reference to “ADS1115::readInput(int)”

Am I needing to put the address 72n somewhere in the files?

Thank you,

looks like its not finding the .h and .cpp files.
no, you dont need to put the address, lib will work with the default address.

This is what I have using the Particle IDE. Am I doing something wrong. I created the ads1115.ino file, then the plus sign on the right to add the .cpp and .h for the library as it is not a library available on the Particle’s IDE except for manual entry.

Got it to work. It’s been a while since I wrote code and naming the ino the same as the library is what I did.