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Comment by jhallenworld | Hacker News Reader

I'm wondering if the USB protocol tax now allows you to run Scheme. I mean if you didn't need USB you could use something like the PIC16F54 (512 ROM, 25 bytes of RAM) for $0.39 each... but you will almost certainly write the code in assembly language. I tried to find the cheapest microcontroller with USB support: I found C8051T622-GM ($0.982), with its luxurious 16KB of ROM and 1.25K of RAM. Curious if Microscheme will run on this- nope, it only supports Atmega..

Atmega32u4 is like $3.43.. too much when you consider that you can buy a keyboard for $4.00.

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> Atmega32u4 is like $3.43.. too much when you consider that you can buy a keyboard for $4.00.

You can buy a McDonalds hamburger for $4.00 too, but if it's something you're going to eat every day let's hope you can do better than that.

I've got a prototype keyboard that is built around a $19 ARM dev board that runs a firmware written in Forth. I tried running that on the ATMega, but 2.5kb of RAM is just not enough.

You can get bare ARM chips for nearly as cheap as AVR, but most people aren't going to be interested in a kit if it requires SMT soldering, so the daughterboard approach actually makes a lot of sense here. Surprisingly it only raises the cost from $4 to $9.

Looks like PICBIT is finally open source: https://github.com/stamourv/picobit

We use(d?) it at U of Montreal to drive small PIC18 robots. Except for the one time I had to debug its GC, it was a fine platform, even for HS students.

I doubt PICBIT (or Microscheme for that matter) could run on the PIC16 family, with it's 25 bytes of RAM. Wouldn't be much of stretch to port Microscheme to PIC18s though (with 512+ bytes of RAM), the code generator is pretty straight-forward: https://github.com/ryansuchocki/microscheme/blob/master/src/...

Original author here.

I have a prototype model of my keyboard that runs a firmware written in Forth. It is built around an ARM Cortex M4 dev board I got for $19. The ATMega doesn't have enough ram for Forth or a real (non-subset) Scheme.

You can get bare ARM chips for practically nothing, but for this project I ruled out SMT since it's intended for a DIY kit and most people don't feel comfortable soldering SMT. An ATMega dev daughterboard costs a bit more ($9 vs $3) but fits the requirements of this project much better.

>I ruled out SMT since it's intended for a DIY kit and most people don't feel comfortable soldering SMT

this is superstition and education issue, not technological one, SMD is EASIER, faster to solder, and cheaper.

People are scared because they have soldering iron and know only soldering iron. Show them hot plate or hot air gun. I dont buy "but they already bought soldering gun, they would have to buy next tool" arguments. Its like peddling wooden car frames, because people have glue already. Soldering with hotair is easier to learn, faster to master, and more versatile.

You have to pick your battles. That may be true, but unfortunately there's not much I can do about it; I've talked to a lot of people who were hesitant to buy an Ergodox when they saw the assembly instructions mentioned a magnifying glass and tweezers.

In any case you can't get around the need for a soldering iron anyway in a kit that includes key switches.

What does a $3 cost difference in the CPU matter? Someone doing this is almost certainly not doing it to save money.

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