Arduino NANO controlling two digital potentiometers independently

Question

Fellow colleagues

A buck/boost device comes with two 10 turn trim pots; 50k for voltage and 10k for current limiting. Having to panel mount these I had to replace the trim pots with std linear single turn pots.

Yes, the my work around causes a less user friendly adjustment.

Solution - I would like to use a Arduino NANO to control two digital potentiometers.

Being a total beginner with Arduio....

1) can the NANO handle two dig pot adjustments independently?

2) must I use one NANO for each adjustment?

Your advice/guidance will be appreciated.

Apologies in advance if something has been posted/answered already............ just soooo much good info on the site.

Thx

AT

Gough Lui · Answer

Even with the same I2C address, throwing in an I2C expander/mux would allow them to be addressed independently. - Gough

michaelkellett · Answer

You need to post the schematic of the buck/boost circuit. Can't advise you without because it matters exactly how the pots are used. One Arduino can easily control two pot chips but only if certain conditions re. common earth or reference voltage are met (and there are ways round these problems too .....) MK

alanthom · Answer

Dear MK Thank you for taking the time to guide me. Unfortunately the buck/boost is a proprietary device - no cct is available. GREAT - confirming once micro controller can do the job. The buck/boost cct is inexpensive so I can play around. My Arduino UNO and NANO kit will be arriving soon. Whilst waiting. I'll order the two dig pots and start with some basic Arduino projects. During my tertiary education, "modern" programming was in its infancy.....Olivetti Basic, Fortran and did a bit of assembler for Z80 chip. Did not love it and continued with analogue electr eng. How the wheel has turned..... Now, at the ripe age of 57.... I have to get to understand Arduion code.....lol Thanks Alan

fmilburn · Answer

I have used the MCP41010 and it is easy to use. As Doug states above, you need only add a second pin on the microcontroller as Chip Select (CS) for a second pot since it is a SPI device. Select and deselect by holding CS low to all devices and then high individually when selected. There are also 2-channel devices like the MCP42010 that have 2 pots on one chip. Googling the part number and Arduino will turn up additional information.

michaelkellett · Answer

Hello Frank,

The Arduino can work the pot OK, but the pot might not work in the PSU circuit.

The problems start when you use a 5V supply and connect one of the pot ends to a higher voltage (just like you normally would if connecting it to make an adjustable voltage feedback set up).

Any of the pins more than 1V above the supply pin and expect the chip to fail. Any of the pins more than a small amount (perhaps 100mV) above the supply pin and the pot won't work properly.

There are always work arounds but they get very tricky if both ends of the pot "track" are at high voltages.

When we know the voltages on the mechanical pots we can work out how to make it work.

MK

dougw · Answer

You can control multiple digital pots from one microcontroller. If the pot uses I2C for communication it usually has some address pins that allow each pot to have a unique address. If the pot uses SPI, the chip select pin on the pot allows the MCU to use a different MCU pin to select each pot.

michaelkellett · Answer

You're thinking of using an MCP41010 - beware - this part needs a 5V power supply and to share ground reference with the Arduino. None of its other pins must be connected to a voltage exceeding supply + 1V or it will be damaged. None of the other pins must be connected to a voltage above 5V or iot won't work correctly. If, as I suspect, your buck boost is a bit like this one in this article: https://wiki.beyondlogic.org/index.php?title=WD2002SJ_LTC3780_Synchronous_Buck_Boost_Converter_Ebay_Automatic_lifting_pr… where the voltage and current control features are described, then the voltage control pot is connected to Vout and you could not use an MCP41010. (the actual value of the pot is not very important, since the other resistors can be scaled to suit.) You can't just drop a digital pot in place of a real pot in any circuit and expect it to work. Unless you have the schematic you are setting yourself up to fail (in a smokey way !). If all else fail then trace the circuit board out yourself and draw the schematic - it will ensure that you really know what you are working with. Or post some pictures and someone on E14 may be able to identify it. MK

fmilburn · Answer

Remembered this Energia (fork of Arduino for TI MSP430) library I wrote some time back: https://github.com/fmilburn3/DigitalPot_MCP41010

dougw · Answer

it should be pretty similar to this example: MCP41010 Digital Potentiometer Arduino Users Manual | Henry's Bench

fmilburn · Answer

Michael,

Datasheet states “Single supply operation (2.7V-5.5V)” and I have used it at 3.3 V but I readily defer to your knowledge if I missed something

Disregard me. You are referring to over voltage.

Frank

michaelkellett · Answer

That module looks sufficiently different to be uncertain of which regulator chip it uses and how the pots may be connected.

You could try measuring the voltages at the ends of each pot (not the wiper) with respect to zero (gnd) over the range of operation.

If within the range 0-5V - OK, if not then you just can't avoid some trickery and you will get on much better if you know a bit more about the circuit.

I expect that you realise that this module (sub $5 ) will be pretty awful in terms of quality of parts - expect it to be disgustingly noisy (electrically).

MK

Arduino NANO controlling two digital potentiometers independently

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