So I’ve now spent hours reading all kinds of Forum discussions of Photons and Motors but it does not appear that anyone has tried this one yet. I’m working on a hydroponic control system that uses many motors (circulation, dosing, valves, etc) so I need to use i2C in order to connect them to the li…

Pictures coming shortly. In the interim it became more mysterious. I tried hooking my pair of resistors (10K now) to 5vdc instead of 3.3 in case the motor controller required 5V to operate. Then I pressed the reset button on the Motor Controller at the end of a failed scan and it immediately dete…

Just an FYI, if the VCC for your motor controller is 5V, that is going to be troublesome to connect it to the Photon I2C lines, since they are 3.3v. In other words if the Atmel processor on that motor controller is running at 5v then is will be an issue. Check into that first before continuing, Al…

@mikemoy , I2C is agnostic whether you are running 3.3V or 5V logic as long the pull-up resistors are tied to the correct level. Since I2C only actively pulls LOW but “delegates” the HIGH level to the pull-ups you are good to use 5V I2C devices on a 3.3V µC without level shifting.

Photon docs show that no special conversion is needed for 5V even thought the Photon is a 3V3 device as long as the pull-ups go to 5V. I’m curious what is the basis of your assertion that 10K is too high for I2C - all the docs I’ve seen recommend using either 4.7K or 10K.

@Mattster , I2C can be finicky and using 4.7K pull-ups with those “longer” wires may be better. Looking at your pictures, I now realize that the only power to the motor board is via the Grove connector which is supplying 3.3v, not 5v. In addition to that, the 3.3v supply on the Photon can’t possib…

This comes from many years of designing systems. The majority of people never look at the I2C or even SPI lines with a oscilloscope to actually make sure things are ok. They read something online somewhere from another who just guessed and they assume that’s the way to go, never even bothering to re…

@mikemoy , I dare to contradict - again - about the level shifting for I2C. I²C is (in parts) specially designed for mixed voltage architectures and so are the 5V tolerant pins. While it’s best to opt for a homogenous design, sometimes you may be stuck without the choice and for that’s perfectly fi…

Mixed voltages for I2C was not even a though when they created it as most things out back then were 5v. It was primarily designed to minimize wire signals & allow many multi-drop parts on the same set of wires, unlike SPI where you need a CS line for each part. If one were to take a look at virtuall…

@mikemoy , I don’t disagree with your arguments though I don’t agree either within the “off-the-self and hybrid platform” context. Nonetheless, can you please take this “rant” as you called it to another topic so as not to pollute the original post. Also, instead of a rant, providing guidelines, l…

Problem with Photon and Grove I2C Motor Driver

Troubleshooting

peekay123 August 25, 2017, 2:17am 25

@Mattster, see my response on another thread:

I2C Pull-up Resistors added to Photon motherboard Request

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Problem with Photon and Grove I2C Motor Driver

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