Hi all - I'm looking for the best/safest way to power both my Uno R3 and the Adafruit Motor Shield v3.
I'm using a 5v Regulated power supply that can handle 4 amps. The motor shield will drive 3 DC motors which are each part of a motorised potentiometer assembly - details here: https://www.bourns.com/docs/product-datasheets/PRM16.pdf
The motors are designed for 4.5 v at around 100mA.
I understand that I can hook my power supply directly to the Power In on the motor shield for powering the motors.
My question is - can I use the same power supply to also provide 5v to the Uno for logic control?
Would it work by just adding the VIN jumper to the Motor Shield or is the 5v too low as this ends up going through the Uno regulator which is expecting a higher voltage?
If that's no go - can I connect the 5v supply directly to the 5v and Ground Pins on the Uno. My understanding is that's safe to do with a quality, well regulated supply, which I have but is there a better way?
I'm also concerned about potential noise issues with having the motors and logic running off the same supply - I don't have the option for runing an additional supply or using USB so I'm wondering if I could make a little filter circuit right after the supply to create two isolated outputs - one to feed the Uno and one for the motors?
Power the Arduino Uno and Adafruit shield using a parallel wiring setup. Do not use the VIN jumper with a 5V supply. The Uno VIN pin requires at least 6.5 volts to function. A 5V input drops too low through the internal regulator. This will cause unstable logic behavior and frequent microchip brownouts. Instead, split your 5V 4A supply into two distinct paths. Connect one path directly to the shield motor power terminal block. Connect the second path directly to the Uno 5V pin. Always disconnect USB power before turning on the external supply. Bypassing the internal regulator removes standard reverse polarity and overvoltage protection.
Even Adafruit recomends using two separate supplies. You can try just one, maybe it will work since your motors don't use a lot of current. Connect to the Uno 5V not Vin.
Thanks for your reply - the parallel paths from the supply sounds the way to go. I'm also running a HT16K33 Display driver for some 3 digit 7 Seg displays that will likely benefit from it's own 5v path from the supply as I think all the displays on at once plus some additonal independant LEDs could potentially draw too much current to be fed power via the Uno.
I'll connect one path to the 5V pin on the Uno, one to the Motor Shield for driving the Motors and one to the HT16K33. I can easily add reverse polarity protection from the supply. Have also looked at these little Recom 5v to 5v DC/DC Convertors which could offer some additional isolation between the 5v paths from the regulated supply (also a Recom block). They're good for 200mA of output so only useful for placing before the Uno in this case. Wonder if you or anyone has had any experience with using them?
Thanks for your reply. It was reading the Adafruit guidance that raised my concern on how to best achieve what I'm looking to do. The project is running off 240v from the wall through a Recom voltage regulator block which outputs 5v at 4amps. Think I might have limited my options somewhat by converting straight down to 5v when it comes to providing isolated power supply paths for the different elements of my circuit but I'm commited to this road now so will endeavour to make it work by taming as much of the noise as possible. Cheers.
Yep, spot on. I'm confident now I'm not going to blow anything up and am busy wiring everything together in a test circuit. Will report back how I get on. Cheers
Awesome project. I am looking to built a similar project with 3 bourns motorized potentiometers. Basically for an amp, having 4 (or 5) presets and maybe a remote pedal (MIDI controlled). I am waiting for the pots to came. Something like a Neil Young Whizzer, with motorized pots.
Sorry for late reply. Yeah offloading the HT16K33 display driver is the right call. It prevents heavy current from glitching the Uno traces. Splitting these parallel wires requires reliable connections. You can find this write up helpful to make solid, vibration-resistant power distribution. Wire splice types Adafruit's guideline also must be followed.
The RECOM RO-0505S provides excellent galvanic isolation. It completely blocks high-frequency motor noise. However, it has a strict 200mA current limit. Your Uno naturally draws 50mA, leaving 150mA headroom. Unregulated converters also require a minimum load. Without a load, the voltage can spike dangerously. Fortunately, the Uno draws enough baseline current at boot.
The main catch is isolated grounds disrupt I2C communication. The Uno, shield, and display driver require shared grounds. Reconnecting the grounds defeats the RECOM module's isolation.
To fix this, use an ISO1540 digital isolator. This passes data signals across the isolation barrier safely. Alternatively, stick to parallel paths with an LC filter. The LC filter blocks noise without breaking ground connections.
Here is the ISO1540 digital isolator datasheet.
Thanks so much for your helpful response. I wondered about whether sharing the grounds would defeat the usefulness of the RO-0505S. I'll check out the ISO1540 for sure and see how that little bit of kit works. Thanks for the datasheet. I see Adafruit has a module for these too.
Otherwise using an LC filter might just do the trick. My motors are only being used to turn control pots into preset positions and won't actually be running that often so I might be overblowing the potential noise issue. I'm in the process of wiring up the full circuit on a test bed to better ascertain how much filtering I might need for it to opertate effectively.
Thanks for the info on wire splicing - that's a helpful article. All the connections will be well soldered in the final iteration and my practice here is pretty solid - I'm using the arduino to add digital controls to a usually all analog audio amplifier and it's the digital stuff that's providing exciting new ways to trip myself up:)
Also explains why I'm hot on the potential for noise as I need to ensure its kept out of the audio path as well as the digital brain. Will forge ahead - cheers
Adding digital brains to analog audio changes everything. Audio paths are incredibly sensitive to digital noise. Motor brush arcing causes nasty ticks in speakers. Ceramic capacitors on the motor casings are mandatory.
Using the RECOM module and ISO1540 is standard audio practice. This combination completely prevents digital ground loops. Digital switching noise will otherwise cause high-pitched whines. Isolating the Uno ground keeps that garbage sealed away.
Your test bed is the perfect next step. Turn the amplifier volume up without playing music. Trigger the motors and change display digits. Listen closely for any speaker artifacts.