Left module flickering with mobile phone

Thought I’d start a topic about an issue which I’m aware at least a few people have experienced. Which is that the left module’s connection can flicker on/off if your mobile phone is placed to the left of it.

I realised this initially when I tried to capture a video of it happening and couldn’t do it, realising that the act of picking up my phone resolved it. These days I keep the phone away from that side of desk. It’s not a particular problem for me, but I’m sure it’ll be a confusing issue for people when they first encounter it.

My suspicion is that the I2C connection between the two halves has less protection against interference than USB. But it might be interesting to hear from actual engineers about this. And also if people have found a way to mitigate it.

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Admittedly, the UHK is rather sensitive to electromagnetic interference, and we send this troubleshooting guide to our customers when they encounter such issues. We couldn’t catch this issue in the design phase, but fortunately, people can almost always work around it.

I2C is a likely reason; the bus is too long and has too many ICs on it. Future UHK versions will use UART between the halves. Another possible cause is insufficient ground pour on the PCBs, which will be much increased in future versions as well.

Useful to know. Would be useful to have that page in the knowledgebase maybe? As I mentioned, it wasn’t an issue for me once I realised the phone was causing it.

On a side-note, I find the whole idea of communicating over wires kinda fascinating. Last week I chanced on a steam railway and found myself in the signalling room. Long before there was telephone, they have, and still have, an electrical system for communicating between stations. From memory one pulse was to get their attention, two pulses means the train is leaving. It was also connected to a locked token system, which I think is the earliest use (that I’ve come across) of the term ‘token’ to denote something that gives you a permission.

This troubleshooting guide is already part of the knowledgebase. For example, it appears when you type the “flicker” word. I’ll create an index showing all articles.

I’m also quite fascinated by the entire system design. Thankfully, we have digital communication now. In a way, the UHK is a network of tiny computers talking to each other. I wrote a guest article on Toptal way back. A lot has changed in the meantime.


I started experiencing this interference back in January. I started getting it right after I moved across the country. I initially thought the keyboard got damaged in the move. Discovered at the beginning of the summer that my phone was the cause of the issues. Keeping the phone further away certainly is a decent solution but it’s a bit inconvenient for my setup. Is there any more detailed guide about how to use the foil to protect against the interference?

Please try to apply aluminum foil on the entire bottom sides of your UHK. If it doesn’t work, you may need to apply it on the sides, too, in which case the end result won’t be pretty, unfortunately.

Alternatively, halving or further decreasing the default communication speed of the UHK by using the set i2cBaudRate 50000 smart macro command in the $onInit macro may work at the expense of reduced responsiveness.

Are you saying I should put foil around the outside of the plastic UHK casing? Or around an internal part of the left keyboard half?

I mean outside. Putting the foil inside would short electronics, so it’s strongly unadvised.

Glad I came here to check. I have messed up several emails and Slack messages in the last 14 months because of this and wasn’t happy about it. Hopefully this is it ! Thanks