microtherion has published new project the ChipHeadBang, that is available on Github:
Design for an USB to Serial converter with ICSP header for (slow) bitbang programming, based on the CH340G chip.
While this seems to work pretty well, and the CH340G can be obtained extremely cheaply from sources such as AliExpress, driver support can be a bit iffy. For current versions of OS X, the vendor provided driver will cause kernel panics, and as far as I know, only this commercial alternative will work
The title of this summary gives the impression at least to me that this is supposed to be a ICSP programmer as the main feature but the actual article is about using a cheap USB to serial chip instead of the more common but more expensive chips. The ICSP connector is a bonus “free” feature you’d use to bootstrap a real programmer.
“My understanding is that the Linux and BSD drivers are OK, but the Windows and Mac drivers are not properly signed, and the Mac drivers will actually cause kernel panics on the latest versions of OS X. I was quite satisfied with quality of the commercial third party OS X driver I ended up buying, and the price is very reasonable, but if building a cheap solution was the objective in the first place, even that reasonable price does of course spoil the economics (if not the hedonics) of the exercise. ”
Erm. Yeah. I think I’ll give the CH340G chip a miss for now! Dealing with the Prolific and FTDI drivers is already a hassle. I don’t want to also deal with unsigned drivers and ones that crash your system.
Another FTDI/Prolific alternative is to use a PIC microcontroller. The PIC16F1454 is around $1 and can be programmed to be a CDC serial adapter. (It also doesn’t need support components that are not exactly free like a crystal.)
Going CDC uses Windows/Linux/whatever’s existing driver, and the PIC firmware can be customized for the particular application.
I tried to take some of the PIC pain out of it with an open-source bootloader and example code (see website). With the bootloader, downloading your own custom code to the PIC is easy
The gotcha is that unless I can somehow get an entity to start selling pre-programmed chips to individuals, you still need a PICkit to program it the first time with the bootloader.