What Remains to be Done

Published on 2023-08-29 in PewPew LCD.

I had a bit of a break on this project, caused both by my lack of motivation, and by the chip shortage, meaning you couldn’t get any SAMD21 chips (or anything that could easily replace them) anywhere. The shortage is apparently ending this September, and I have also recovered some strength, so I can think about the project again.

The time that passed wasn’t entirely wasted. I got to test the device in different conditions, with different computers, different programs and different batteries, and I have discovered at least two serious problems that require my attention, and that could lead to an increase of the price of the device.

The first problem wasn’t immediately apparent with the simple games I tested the device with, mostly because they check for button presses pretty often. But not all programs written for PewPew devices do that, and the less frequently they check for the presses, the worse the touch buttons on the device work. You see, originally the pew library would use the same interrupt it used to refresh the LED matrix to also check for button presses, so the checks were very frequent and were happening in the background. When it was ported to other devices, it used the keypad library to also keep checking the presses in the background at a high rate, and processed the resulting events when the game asked button presses. But there is currently no keypad library for touch pads in CircuitPython, or any other way of checking for touch in the background. So the pew library for this device only checks the pads for touches when the game asks it. And that means that if the game doesn’t ask often enough, some touches will be missed. And that results in an unreliable and laggy feel of the games on this device. It simply is not pleasant to use it. We can’t allow that.

I can think of two ways of solving this problem. The first is to fix it in software and write a library similar to keypad, but for touch. This requires some datasheet diving to be done right, without slowing the code running in the foreground on the device. I’m not entirely sure I can do it, but I will try. I can think of two ways of doing it, the harder, with interrupts, and the easier, with the system tick. If I don’t manage to write such a library, the only other solution I can think of is to add back physical buttons to the device. It would increase the price, yes, but it would also immediately solve the problem, as I could then again use the keypad library, and it would provide the users with tactile feedback, further increasing the pleasure from using the device. Plus, buttons are really not that expensive, even the nice ones.

The second problem has to do with batteries. You see, the kind of coin batteries that this device uses are not the same all over the world. When I designed the prototype, I tested it with batteries I bought in Switzerland, and they had no problem driving the display and the microcontroller. However, when I went to a conference to UK, and bought some batteries there, they proved to be too weak to even start the device. I can only assume that regulations in different countries require different power from the same type of the battery, and naturally batteries destined to different markets differ in quality.

Again, there are several ways I could solve this problem. I could switch back to two AAA cells, instead of a coin battery. I could require a thicker (and more expensive) variant of the coin battery I’m using, or even a bigger (and harder to obtain) one. I could remove the battery slot entirely and say that the device should be connected to USB for use – after all, that’s how it would be used during the workshop, which is the main target for it. But a simple boost converter circuit would work too, and it would also make it run on the same battery longer, draining it more completely before failure. What’s more important, it would feed the device a consistent voltage as long as the battery had enough juice left in it. And there are ready boost converter chips out there for really cheap. It would add to the cost of the device a little, and complicate it a bit more, but I think the increased reliability and use of the battery is well worth it.

So I need to redesign the prototype to add a boost converter circuit to it, complete with a small inductor and a controller chip, and some beefy filtering capacitors. I have already tested a similar circuit in another project, and it works very well, so I’m optimistic about this.

There is a third problem, but it has more to do with logistics than with the hardware. I don’t want to be selling those devices myself. Sure, I can order a batch for a workshop or two, but I don’t want to have to run to the post office to fulfill orders. But I want other people to also be able to run workshops with them. That means that I need to make them as easy to order as possible, and that’s done easily by re-doing the design in EasyEDA instead of Fritzing. With that, people can simply open the designs without having to install anything on their computers, change the silkscreen according to their needs, and order the device assembled with a few clicks. Well, mostly assembled, they would still need to buy and solder the displays.

Unless, of course, I switched to some kind of displays that are available from LCSC, like the small OLED screens I used in the PewPew OLED . Come to think of it… hmmm…

Anyways, I have some work and some decisions before me.