I2C Reay Board - strictly 5V?


the product description of “16-Channel General Purpose SPDT Relay Controller with I2C Interface” mentions only 5V at the I2c port.

As my Teensy 3.6 is ONLY 3.3V, I wonder if there is a way to use the relay controller without switching to a Teensy 3.5 or introducing level shifters.

What happens if the I2C port of the relay board is run with 3.3V from the master? Are the SDA/SCL lines still 5V?



All of our I2C products operate at a line voltage of 5VDC(on SCL and SDA) this dramatically increases the length of cables that can be used between boards and allows for chaining boards together. At a 3.3VDC line level the cables have to be extremely short. This is why all of our I2C devices operate at a line level voltage of 5VDC.

We make I2C shields for several products that are only 3.3vdc tolerant such Raspberry Pi which utilize level shifters to convert line level voltages from 3.3VDC to 5VDC and vice versa.

I would say you are going to need a level shifter or move to a 5VDC tolerant platform to use our devices.

I am using 2 NCD IO i2c expansion boards… the 8ch relay board and the 8 channel digital i/o board… connected to a RaspberryPI4 via i2c. I also have 6 other i2c devices on the same bus. all of the lines are very short, with no more than 8" between them. I’m sure that I have no more than 20" of total cable length on the i2c bus. I don’t have issues. I do employ .56uF capacitors for induction suppression on about 50% of the loads on the relay board (solenoids, motors, etc…)… I don’t bother to do that for the channels that have resistive loads (heaters, super low powered LED lighting).

Your mileage may vary, and obviously I took the risk of purchasing the devices without knowing if they would in fact be reliable. I am content.