electronics

Today I learned how to make PCBs. I didn’t invent anything here, this is all pretty well known by the PCB-making community, but it’s not well-known to me. So I taught myself a bit!

The first part was the design an electronic circuit. I decided I was short on time, so I grabbed an existing schematic.

Next, I downloaded KiCAD, and recreated the circuit there. I found this video tutorial very helpful to learn kicad.

Next, I made the actual PCB layout.

To my surprise, after a little jiggling I got it down to a one-layer design.

That means home-printing would be much easier. No having to line up the two sides carefully.

I printed out the image on paper (backwards) on my toner printer, and taped it to the copper-clad PCBs.

First, I tried laminating it. Almost no ink transferred, and the paper came off easily. Then I tried ironing it, but the paper stick to the iron and not to the PCB. The tape melted on the iron. For both, I dunked them in water after, which is supposed to help loosen the paper.

Next, I tried the standard advice–sand the PCBs (I used 320 grit) and use glossy paper. This time, both pieces of paper stuck very well. I was wary about the iron coming off again, so I just left it on place on the highest heat–this worked fine for adhesion, but I had to iron out wrinkles at the end. The laminated piece had lose edges, while the ironed piece was on there totally flat.

I tried peeling off the laminated paper–oops! It peeled back and most of the ink stayed on the paper. I think if I took it off more carefully, it would have worked.

I picked at the ironed paper a bit, but it didn’t budge. I let it sit in dish soap for a while so the paper would fall apart. The first hour didn’t do anything.

Meanwhile, I made an order at PCBWay. It’s still under review.

Edit: after some advice from a friend, I peeled off this paper more aggressively, and scrubbed it off. The ink was fine. It doesn’t look great, but I think this is mostly the wrinkles during transfer. It’s a little blurry, I’ll have to do a third attempt before I try etching.

I’ve been prototyping an e-ink laptop.

a wooden box with a keyboard inside and an e-ink screen mounted to it

a closed wooden box with a keyboard visible through a hole in the front — Closed “laptop”

I’m not the first, there have been many other such devices before. I came up with the idea independently, but the specifics are heavily inspired by the Ultimate Writer by NinjaTrappeur in 2018. Similar to him, my use case is typing without distractions, and reading books. E-ink displays are quite slow to update, so I don’t think it can serve as a general purpose computer. Here’s a video of it in action. It operates at one frame per second.

The electronics are not fully done. They need better secured, and I’m going to redo the cabling and power back.

an e-ink screen reading "hello world" — I broke a screen over-tightening a nut. That said, I like this look pretty well! If the lid was thicker, I know how to avoid screws on the other side, too.

a e-ink screen loose on a desk, covered in garbage — Early screen progress. I got *something* to display, but not what I wanted.

a mechanical keyboard in a box — I found a really nice, cheap mechanical keyboard on ebay. The main downside is that it’s heavy–730g. It also consumes heavy amounts of power, even when not in use. I have a nearly identical keyboard that doesn’t, which I’ll use for v2.

a homemade battery pack with four red lithium-ion batteries — I made my own lithium-ion battery pack. It works well, but it doesn’t quite fit so I’m going to redo it with one less cell. It also needs an on/off switch and a right angle USB cable.

a close-up of a raspberry pi in a box — The prototype is powered by a Raspberry Pi 3. The final version will use a microcontroller to save power. The Pi Zero can also be swapped in with no changes, and uses a third of the power. But it’s noticeably slower and takes 30 seconds to boot. For prototyping I’m using the Pi 3 for now.

I’m not the best woodworker, but I’m slowly learning. Here are pictures of case and lid action.

back view of a box with hinges — Hinged lid. The screen is on the bottom of the lid.

back view of a wooden stop, closed — A wooden stop on each side

back view of a wooden stop, open — Wooden stop with lid open. It hits the bottom, bringing the lid/screen to a rest at vertical.

picture of a latch, open — Latches on the side

close-up of a hinge in cracked plywood — Don’t put hinges sideways into plywood. But if you do, drill big pilot holes. Out of six screw, one cracked a little.

On the software end, shout outs to:

the creator of the ultimate-writer software, NinjaTrappeur, who has been encouraging (and explained the right way to rewrite the stack, if you wanted to today).
Ben Krasnow, who made a video about how to hack partial refresh on an e-ink display.

There’s a few things I’d like to polish still–even as a prototype this isn’t fully done.

The raspberry pi and battery pack are currently sitting loose. They need secured, especially since they can fall out the open front.
The software has some major problems. It doesn’t support Control-C, etc in linux, a must, and it doesn’t update the screen at boot until you press a key, which would be nice to fix.
There’s no power switch. Right now you have to unplug it manually.
I’d like to add a carrying handle.
I’d like to tuck away the electronics behind a panel. They’re ugly.
The wood looks rough in a few places. I want to hide some splintered wood, screw holes, etc.
The USB cables have too much stress on them. I need to make a little more room in the wood, and use a right-angled connector in one place.

There’s also no default software, but that’s a feature. A prototype is for figuring out how I want the interface to work, and what I want it to do.

Parts list

7.5 inch e-ink screen from Waveshare (not particularly good) – $60
Raspberry Pi 3 (Pi Zero, etc also work with no changes) – $35 (but unavailable)
microsd card – $7
Plywood and boards, wood glue – $15
Plexiglass (to cover screen) – $10
Bolts, washers, and nuts to secure it. – $5
Circular window latch x2 – $8 (or use $10 smaller version)
Hinge x2 – $2
Total: $142

Power budget (at 5V):

Keyboard: 500mW. Other USB keyboards use zero to within my measurement abilities.
Screen: 0-250mW when updating. Hard to measure.
Pi 3: 2000mW. I have the wifi chip enabled (the default) but I’m not actively connected to wifi.
Pi Zero W: 650mW

A real-life test showed 5-6 hour battery life. Theory says (13Wh/battery * 4 batteries / 2.7 watts)=20 hours battery life. I’m investigating the discrepancy. In theory, swapping for a Pi Zero W and a better keyboard would give 72-hour battery life.

Tag Archives: electronics

Hack-a-Day, Day 22: Homemade PCBs

e-ink “laptop”