Two days ago we introduced Capstan, the dial for your rig. This post is not about Capstan. It is about the little round display the largest Capstan runs on, and it is written for anyone with a project on the bench, whether or not a TrailCurrent system is ever part of it. We made a review video of it, built a second project with it that has nothing to do with RVs, and put every file up for free.
Why a post about somebody else's part
TrailCurrent has three goals. Build a real open source Software Defined Vehicle platform. Give it away. Teach other makers how to do the same thing with their own ideas. Most of what you read here is about the first two. This one is the third.
Building a whole system means we spend a lot of time finding out which off-the-shelf parts are good, which are fiddly, and what the instructions leave out. That knowledge is useful far outside an RV. So when we learn something, we share it, even when the person it helps is building a coffee roaster, a boat panel or a desk gadget and never touches our code.
The part in question is the Makerfabs MaTouch Rotary, a 2.1 inch round screen that was $38.80 when we filmed. Makerfabs sent us this one at no charge. They did not see the video before you did, that link is not an affiliate link, and we do not take a video down because a maker dislikes what we said.
You feel it, and that changes things
We already have big touchscreens in the rig and like them. This is a different kind of control. The whole metal housing is the knob. Turn it and you feel a small click for every step. Push it and the entire face, glass and all, moves inward with a click you can feel and hear.
It is hard to get across on video how much that matters. With a touchscreen you look, aim and hope. With this you count clicks and feel the press land, so your hand knows what happened before your eyes check. Three things follow from that, and they apply to nearly any project:
- You get an answer back. Every step and every press pushes back at your fingers. You can use it in the dark, or while you are watching something else.
- It works with gloves on. Glass often ignores a gloved finger. A ring you grip and turn does not care what is on your hands, which matters in a cold shop, on a boat, or anywhere your hands are wet or dirty.
- It fits where a touchscreen will not. It is about the size of a jar lid. A panel big enough to tap comfortably needs a patch of wall. This goes on the edge of a shelf, beside a bunk, or on a crowded dashboard.
One design choice deserves credit. Pressing the dial and touching the glass are two separate things on this unit, and it tells them apart for you. Some round displays make the touchscreen itself the button, which blurs the two. Here a press is always a press. We liked that enough to turn touch off completely in our own project, so nothing happens unless somebody meant it.
A project with no RV in it
To show that none of this depends on TrailCurrent, the first thing we built is a desk tool. Plug the dial into a laptop with one USB-C cable and the computer treats it as an ordinary keyboard. There is nothing to install for that part.
A small helper program on the laptop tells the dial which window you are working in, and the ring of eight shortcuts around the screen changes to suit. In FreeCAD, turning the ring spins the model. In Blender it rotates what you have selected, and a press changes the axis. In Kdenlive it moves along the video timeline, and a press makes a cut where you are. It scrolls in a browser and zooms in GIMP and Inkscape.
If you draw, model or edit video, that is a useful tool on its own. It is also a starting point. Swap in the programs you use and it becomes yours.
Lessons that carry over
The second project in the video is Capstan. We covered what it does in its own post, so here are only the parts worth borrowing for something of your own.
- Do not put a keyboard on a tiny screen. The display is sharp, but there is no room to type a WiFi password on it. Have the device create its own small WiFi network, join it from your phone, and type on a screen made for typing. It takes a minute, once.
- Do not wire every sensor to the thing with the screen. Our dial shows battery, water and air readings, and none of those sensors are attached to it. Other devices measure and pass the numbers along. Small devices that share what they know are easier to build than one box that does everything.
- Show what really happened. When you switch a light from the dial, the picture only changes once the light has actually switched. A control that tells the truth is worth the extra step.
What tripped us up, so it does not trip you
A review that only says nice things is not much use. Here is what cost us time.
- A black screen. With the standard startup settings the backlight came on and nothing else did. No error, only black. The right settings were in one of the maker's own examples, and we carried them across.
- Red and blue swapped. The maker's guide and the maker's sample code disagree about which connections are red and which are blue.
- Missed clicks. The sample code can lose a click or two if you spin the ring while the screen is redrawing. We changed how the clicks are counted so it keeps up however fast you turn.
- No 3D model to design a case around. The maker does not publish one, so lining up the cable openings took many test prints. In the end we went old school: scaled a photo to the published dimensions and drew over it.
The first three are already fixed in the files below, so you start from a dial that works. The fourth is what the next section is about.
A stand for it, and a wall mount on the way
That tracing exercise produced something new since the Capstan announcement. There is now a printable desk stand for the 2.1 inch dial. It sits on a desk or shelf as it is, and it has screw holes for places that move, like a vehicle. Hook and loop tape or adhesive works too. A wall mount that locks the dial in place with a screw is next, and it will land in the same folder.
Should you get one
If you want a control that changes with the program you are using, yes. If you have a project that already works and you want it to feel better in the hand, also yes. It is not the right pick if you need to type on it or show a lot at once. That is a job for a bigger screen.
Take all of it
Everything from the video is free and MIT licensed, same as the rest of TrailCurrent.
- The macro pad and starter examples, with the fixes above already in.
- The desk stand files, ready to print or change.
- The Capstan software, if you want to see a finished dial from the inside.
If the rig side is what brought you here, the Capstan page has a dial you can turn in your browser. And if you build something with a knob that is also a screen, tell us about it in the video comments or on Discord. More like this goes up on the open source channel.