I battery-powered my Digitakt!

[Cannikin]

TL;DR I put 3 x 18650 lithium ion batteries and some electronics in a Digitakt to make it ultra portable. Gallery here: https://imgur.com/a/muZwgLX

I like to bring my Digitakt downstairs and just fiddle with it on my lap in the evenings. This isn’t ideal since it requires 12V. Using a 12V USB-C to barrel jack cord and a battery works, but it’s still some extra junk you have to cart around. I wanted it to be totally self contained. After finding some photos of the internals I saw there’s a huge empty cavity in there. The hard part was going to be figuring out how to convert the variable voltage coming out of the battery pack (ranges from 12.6V when full to ~8V when empty) into a steady 12V.

After some research I went with a 12V step-up/step-down voltage regulator. That gets 12V from the battery pack to the Digitakt itself, but then I need to recharge the battery. I found an adjustable buck/boost converter that lets you dial in both the max current and max voltage, perfect for charging a battery pack like this. Then I needed some way to protect the batteries to make sure they didn’t over/under charge. This BMS board handles that job. Then I wanted a way to indicate the current battery state, and not just wait for the Digitakt to turn off when the battery got too low. This display does the trick, you just need to press a button to turn it on for a few seconds. The only downside to this combination of items was that the 12V voltage regulator draws about 0.03A continuously, even when the Digitakt is off. But, there is a way to put it to sleep which brings the amp draw down to practically zero. To do that, I designed a small circuit board with a transistor and a couple of resistors. It also acts as distribution center for all the various connections.

I designed and 3D printed a bracket to hold all of the components, and using the VESA mount holes on the bottom to secure it. The little blue squares in the photo above are thermal pads so that any heat is spread out on the bottom of the case. To connect everything to the Digitakt mainboard I cut the lead that went from the + of the barrel jack connector to the mainboard. I wired the input of the buck/boost to the barrel jack. I connected the output of the 12V step-up/step-down converter back to the mainboard. Then I ran a wire (the yellow one) from the power switch to my custom circuit board to enable sleep mode. When the power switch is off, the 12V regulator is asleep, and when the switch is on the regulator wakes up and sends 12V to the mainboard. I drilled 6 holes in the front so I could activate the battery level board and see the LEDs.

And it works great! I get around 7 hours of usage, and then it recharges in around 3 hours. I use a bluetooth audio adapter to send the sound to my Airpods Pro and I’m 100% wireless!

Comparison to Other Solutions

I discovered the big battery powered thread and noticed some differences between that one and mine, mainly that it connects directly to the stock 12V power input, not cutting the lead between the port and the mainboard. The side effect of this is that the 12V jack will now send power OUT as well as accept power in. That seems a little dangerous to me as you would normally never, ever expect an input power jack to be sending power out.

They also rely on the fact that, as the battery drains, it eventually crosses a low voltage threshold (around 10.8V) where the Digitakt can’t run any more, and shuts off. I wanted to give the Digitakt the exact 12V it’s designed for the entire time, for as long as the battery’s BMS is willing to provide power, which is down to around 8.9V on my model. With the step up/down converter I’ve got, no matter where the battery is in its voltage range, the Digitakt gets the same, steady 12V.

With the setup in that thread, the battery never gets 100% full (12.6V) because the stock power brick will only supply about 12.1V max. On mine I’ve got the adjustable buck/boost that gets the battery right up to its max 12.6V.

The setup in that thread is much simpler than mine, and if I had found it before I made mine I probably would have done the same thing! But now that I’ve found it I’m glad that my more complex/expensive setup actually has a few benefits, and that I didn’t go through that extra work for nothing.

[shigginpit]

Loving the battery meter! You should also add this to the Digitakt internal battery thread so that the information can be easily accessed by future gear modifiers.

Digitakt modified with internal battery

Elektron event is over, so I can finally reveal my internal battery-powered Digitakt. Works for 5+ hours. Can power a second Elektron machine by simply connecting the DC inputs. Both will work for 2 hours then, good enough for a full live set. Charges with a standard Elektron power supply. It can be plugged in and removed at any time, no need to turn off the machine to move from battery power to wall power and back. A more powerful PSU may get an additional hour of play though. There are no vi…

Great work! Be advised, the biggest problem is that you will not likely see it again without opening the device back up, and others have found that these types of battery mods are not immune from leaking or swelling.

Might be a good idea to check in on it periodically just to make sure that everything stays in tip top shape.

Cool share, thanks!

[Gral_Kerkila]

That is a neat job, well done!

[captain8]

@Cannikin is there enough room in the digitakt to be able to slice it in half horizontally, allowing one to have a much sleeker form factored digitakt?
(minus the battery modifications you made)

[bibenu]

@captain8 pretty sure that this guy knows the constraints there.

My Slim Case for the Digitakt/Digitone

Available now! [The Manually Sliced Case for Elektron Digitakt and Digitone]

[captain8]

oh yeah forgot about that, thanks

[LaVernWinston]

The slimmest you could go is indeed pretty much half of the factory device ironically. So somewhere around 1.25” if you were going to keep it flat with no angle. There would be a ~1.5” forehead though so it would have the model cycles/samples vibe.

[Juniper_Steels]

This is effing cool!

(And thanks for putting the TL:DR at the beginning of the post)

[Cannikin]

@shigginpit

Be advised, the biggest problem is that you will not likely see it again without opening the device back up, and others have found that these types of battery mods are not immune from leaking or swelling.

I haven’t heard of cases of leaking/swelling from lithium ion cells before! I know this is common with the flat lithium polymer cells (keeping them charged at 100% for long periods of time famously causes swelling). You can pack those more densely, but the li-ion cells are so much more robust/low-maintenance (and there’s plenty of room for them in the Digitakt).

[shigginpit]

I worked in the cellular industry for quite a long time. Seen some battery issues you wouldn’t believe even prior to the shift towards li-poly, but hopefully a non-issue for you!

[Augenadler]

Thx for linking the stepup/down-regulator.
Will upgrade my DTII battery-pack for sure.

[Cannikin]

Just note that although that step up/down is amazing, it does draw a little bit of current even when the Digitakt isn’t turned on: between 10-35 mA according to the info on their site. If you’re using the Digitakt and recharging it regularly you probably won’t even notice, but otherwise you’ll come back to find the battery empty after a week or two of not using it.

But, if you can bring the “enable” pin on the board low then it puts everything to sleep and it draws between 2-10 µA instead (per volt on the input side). That’s what my little custom circuit board does: puts it to sleep until you turn on the power switch.