Battery Interrupter for Switch Adapting

It was recently brought to our attention that we don’t have a design for a battery interrupter on the website.

A battery interrupt / battery interrupter is a simple, cheap device that enables you to switch adapt many battery powered electronics devices and toys. The battery interrupt is slipped in between the batteries or battery and battery terminal, breaking the circuit until a switch is attached and closed.

MMC had previously put together a set of instructions for creating one using copper tape and a switch jack:
Battery_Interrupt_Instructions (w heat shrink).pdf (575.5 KB)

battery interrupt

Does anyone else have a favorite design or technique they would like to share?
e.g. There is a similar solder-free version here:

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Maker Works which hosts our program is developing a variety of products which are intended to make AT simpler and more affordable. One is an inexpensive solder free jack for switch adapting items that uses a custom printed circuit board and screw terminals for attaching the wires. Used in conjunction with WAGO 221 Series LEVER-NUTS a device could be switch adapted without soldering. While more involved than a battery interrupter the finished product should be more durable.


That’s very cool, and could certainly be used with a battery interrupter or to directly switch adapt a device.

Do you know where they intend to sell them? And is there an intention to release the design open-source?

If the design files are available, it would be fairly easy to create a 3d printable enclosure for this, too.


Dale Grover, the inventor, is a gifted electrical engineer with a background in AT communication devices. I saw a prototype Switch Modifier before the pandemic but only recently saw the other items in development. He designed a compact solid state switch modifier using a custom circuit board and code. Initially it had a 3D printed case but Dale is currently working on injection molded cases so the device can be economically produced at scale. The result is a product that has the features of the MMC Switch Modifier with a lower component cost, quicker production and smaller form factor.

I honestly don’t know Dale’s plans for distribution but his goal is to help as many people as possible by making the items low cost and user friendly. It would probably be best if you or someone else from MMC talked to him directly. He is looking for some people to test the products and provide feedback. If you let me know who would be the best contact I will work on arranging an introduction.


This is pretty great @brentcourson! Would love to chat with Dale and his plans… is he here on the forum? Otherwise feel free to email me -


@MMC_Chad Dale is not on the forum but I will connect you by email. I look forward to hearing what comes out of the discussion.


A few thoughts about my screw-terminal design pictured earlier: it’s simple, but I think the reality is that most wires are going to be fairly direct inside a toy, and it is unlikely you’d have the slack to just snip a power wire, strip the ends, and route both to a convenient location for the jack, so you’d end up with two wires spliced in. So I’m changing direction (though if the screw terminal design appeals to you, I have the PCBs, and the parts are just DigiKey).

With the same goal of making this a solderless adaptor, let’s just solder some 18 AWG wire (6-12" long) to a 3.5mm jack and provide 2 Wago 2-position lever nuts. Heat shrink for strain relief at the jack. Color code the wires red and black just for fun. Supply an optional inexpensive wire stripper (18-28 awg?). (I’d lean a little towards the ultra-flexible silicone rubber insulated wire.)

Another issue is the thickness of plastic enclosures. It’s not unusual for the wall thickness of toys to be over the 0.07" or so the typical 3.5mm rear-mount panel jack can accommodate. So think about using a front-mount jack (example:, though this one is very expensive). There’s no problem with the wires passing through the hole from the outside–just don’t put the Wago’s on until after you insert the wires through the hole. Or, there are some rear-mount that go to 3mm thick (0.118") like: I haven’t done more than a quick search, so better ones are probably out there.

The only downside that comes to mind is that Wago’s have a little mass, so they’d bounce around if not secured with a twist-tie or hot glue. A soldered joint with heat shrink isn’t going to do that. I think the tradeoff of not required soldering skills may be worth for some cases.


On the topic of battery interrupters, a flexible circuit board version could potentially reduce or eliminate the problem of wire fatigue at the PCB that seems to plague at least some versions. A 20mm x 120mm flex pcb, qty 100, is $2.25 each delivered. (10" long for $2.62 each.) One end would be circular, goes in between cells or between a cell and the battery contact, gets thinner (maybe 1/4"), and the other end maybe has a 1/8" jack soldered to it, and/or holes for wires that go off to a jack.

Are flex PCBs (polyimide) robust enough for this? Seems like. Not sure what plating would be best. They’re 0.1 to .3mm or thicker, so should work with most battery holders in terms of not adding much length.

This is something that would require a central purchase due to the setup charges and quantities to get decent pricing. But might be a big upgrade over the PCB disks we’ve been using forever.


Welcome to the Forum, Dale, and thanks for sharing your thoughts.

I like the idea of exploring flexible PCBs as a more robust battery interrupter method and as an alternative to the metallic tape methods. Should be able to coordinate with @MMC_Milad to get a test batch ordered.


Welcome to the forum Dale (@dgrover).

The battery interrupter using Flex PCB is awesome idea.

I am testing an input interface using flex PCBs myself and hoping to do a test run in few weeks.

I can definitely order the test batch for our team to test it out. Can we have access to gerber files or the order should be done through you directly?


Just an idea–I don’t have a design for the PCB.
Some elements to include:
–“bulls-eye” circular end, with active copper only in the middle, a bit less in diameter than a AA cell, but (isolated) copper or silk screen circle as guides for C size, and the overall PCB the diameter of a D cell, so one could cut away the excess with scissors to match whatever size is needed without shorting the layers, but still have the pcb diameter help center the contact
–pads for through-hole 3.5mm jack (I’m finding stereo ones are a bit cheaper/easier to find than mono)
–holes/pads for directly soldering wires (might be shared with the holes for the jack): larger holes for insulated wire to pass through for strain relief, smaller holes/pads for soldering the stripped wire
–neck down the width between the ends to make it easier to route in the battery compartment

What layout software do you use? Would KiCAD work?


The different size option would be very useful and neat idea.

I wanted to ask you about it but you answered most my questions.

We have been using SJ1-3535 (3.5 mm stereo ) in many of our PCB based designs as you can get them way cheaper in bulk from alibaba or aliexpress. There seems to be sourcing issue with it at the moment. The vertical profile of the jack is not idea for every design though.

We use EAGLE mostly as you can export designs to FUSION 360 for enclosure design and validation. I have not used KiCAD for a long time but should be okay.

Created a dedicated thread for the flexible PCB version here:

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