Hey friends,
Sharing some recent updates from projects I’ve been working on in August. A few other things are still in progress and not quite ready to show. More on those in the coming weeks. In the meantime here’s what I’ve been up to.
The first project I tackled this month was building out the frontend redesign of Cashu Brr. The redesign was based on work from Veronika, who designed Sovereign Note, which won second place in the ecash note design contest.
Veronika decided to start contributing to Cashu and Brr felt like the perfect starting point. She put together a design in Figma and I used Cursor to vibe code the front end. The new version of Brr now includes the contest winning notes and a streamlined design.
This was a big effort on my part. Close to 20–30 hours of work, mostly due to the complexity of live note previews. Users can enter an amount and it renders directly onto the SVG with the right font and color in real time. After a lot of back and forth, but I finally got it working.
You can try the updated app here. Huge thanks to Veronika and to Gandlaf, the original creator of Brr. I’m excited about where this redesign takes us. It makes adding new notes easier and I think the tool will only get better from here.
Another project I’m really excited about is the CDK LDK Node. This was a big learning experience for me. thesimplekid built entire app is built in Rust. We’re using Maud, a Rust crate that lets us inline HTML and CSS directly to to build web a GUI. He asked if I could help with the design and I jumped in.
The goal of this tool is to let users with an existing LDK node connect to CDK (a Rust implementation of Cashu) From there they can spin up a mint and manage it while also handling normal Lightning functionality like opening and closing channels or viewing transaction history.
Right now the design is still in very early stages but we’ve laid out a solid version 0.0.1. It’s all HTML and CSS. No JavaScript. Which makes it fast and lightweight. The little spinning globe was done with css which I thought was pretty fun.
There’s a lot more potential here: A more robust Cashu mint manager, packaging it for platforms like Umbrel or Start9, and deeper design iterations. For now I’m happy with this early version and looking forward to building on it.
I also revisited the design for the Cashu BTC Pay Server plugin. The aim is to let merchants easily accept Cashu payments through BTC Pay and onboarding is the first problem to solve.
We focused on making sure that after running through setup a merchant is ready to receive payments right away with the lowest friction possible. Depending on their BTC Pay configuration, merchants will have three possible acceptance modes:
Auto convert → Automatically melt all ecash to Lightning.
Hold when trusted → Hold ecash from whitelisted mints, melt all other ecash.
Trusted mints only → Only accept ecash from whitelisted mints.
The next challenge is wallet settings and fees. Should merchants or customers pay them? Should they even be visible or abstracted away? And if merchants choose to store tokens, what limits and controls should they have?
Now that we’ve laid out a solid onboarding flow I’m going to continue refining settings and fee mgmt in the next iterations.
On the personal project side, I built my first SwiftUI project: SL Tracker, a Stockholm Metro departure tracker for iOS.
I was frustrated with the existing SL app. It takes too many taps just to see when the next train was leaving. I wanted a simple widget that sits on the home screen and shows upcoming departures at a glance. So I built it. You can just do things.
I did my best to make this clean, minimal, and follow Apple’s design guidelines. It’s available now on TestFlight. For my first app I’m proud of how polished it feels. I’ll keep iterating on it, learning Swift, and having fun with the process.
Lastly I gave a talk at Bitcoin++ Privacy Edition. I spoke about the current state of Cashu design. The risks, challenges, progress, and what’s ahead. I was also invited to serve as a hackathon judge, which was an honor.
Bitcoin++ events are the highest signal events you can go to. If you haven’t been to one yet I highly recommend it. Later this year there will be a Lightning ++ in Berlin during the first week of October and I’ll be there.
That’s it for this month’s update. Thanks again to everyone building alongside me who helps makes these projects real.
See you online,
Erik
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