I’ve since written up my experiences with printing at 3rd party services – it’s not without their own issues:

https://saccade.com/blog/2019/12/fit-testing-block/

These have enable and phase. Phase as described is direction, enable is being used to turn the motor on and off. The original code (I think) uses this as a PWM speed control. Because you want a change in frequency for the step and direction pins on a modern external stepper controller you need to convert that pwm with a variable duty cycle and presumably some fixed frequency to a 50% duty cycle variable frequency signal.

I would probably stick an arduino in like I said and read the pwm low passed as analog and synthesize the speed to run the stepper from either a function or lookup table. a pro mini is about the size of a postage stamp so it’s not like you’re hanging an arduino uno off of the thing. The other option is you could do it in a more analog way. An LM331 and support circuitry would be a solution pretty small and could probably be tuned to do exactly what you need in terms of range of voltage inputs and frequency drive output. Without using any ‘specialized’ chips you could use an op-amp to do the same thing but the setup is a bit harder: https://bestengineeringprojects.com/voltage-into-frequency-converter/#:~:text=The%20circuit%20of%20voltage%20into,converted%20to%20its%20corresponding%20frequency.

Oh, all of this ignores the lack of an ‘enable’ signal which modern stepper drivers seem to want. Step, Direction, and Enable. The last one basically says that when you’re not moving do you lock the steppers in place or let them spin freely. No enable signal means your stepper controllers are burning whatever current they drive with all the time holding the motor stationary. This isn’t a big deal when you’re constantly extruding anyway but can be a bit un-nerving to have your motor sitting there burning current whenever the unit is on.

That’s all without changing the code for the atmega168, which you totally can do. But the amount of changes you want to make is up to you.

I’d think it wouldn’t be too bad to take the pwm signal for the h-bridge and use it to drive the stepper. You’d have to make some decisions about max speed and scale that to max pwm. I would probably stick an arduino pro mini where the h-bridge is as a matter of simplicity and drive any off-the-shelf stepper driver from that. You’ll probably end up filtering a couple pwm channels and reading them as analog before synthesizing stepper driver signals. You may be able to do it entirely in logic gates but that design really puts you at the mercy of chance that it will move even close to the rate you want it to. I did something similar turning step and direction signals into quadrature to drive ancient shop bot motor controllers with a modern cnc brain. Then again, if your goal is historical accuracy I bid you good luck searching to find out how it used to be done. I’m currently trying to revive my old c64 dtv board and all the information is websites on the internet archive now.

I don’t want to get a web browser running on a Commodore-64! I’d just like to get my Commodore-64 and its floppy drive working again to play Jumpman, and my Amiga working to play Arctic Fox.

Those statements are both literally true and metaphorical for what I want from the CupCake. I don’t want to go buy an E3D hot end and a RAMPS board set and build a no-name printer in a CupCake frame, and I don’t exactly want to uplift the CupCake into the modern era. I want to get the CupCake working the way it was starting to work back in the day, but I lacked the time to dedicate to completing the job. I’d like to add only a few upgrades, like the Wade’s geared extruder and the TwoTimes low-rider X-Y carriage, that were available at the time.

Part of my interest is historical preservation. I’m privileged to own a pre-release printer from the company that catalyzed the hobbyist 3D-printer revolution, and I’d like to get and keep it working as close to original condition as possible. I’ve visited the Altair display (apparently now dismantled) at the New Mexico Museum of Natural History and Science more than once; and as reverent as I felt about the exhibit, the machines there were doing nothing. I’d much rather keep the CupCake working, if at all possible.

Finally, I do have some ulterior motives.

I love printing in ABS; but in my experience, it requires a heated chamber and gentle air circulation, neither of which my Prusa has. Yes, I could build it an enclosure; but the ABS I’ve bought for it doesn’t stick to their PEI sheet nor (strangely) to the same kapton tape I use on the CupCake. Albeit at a lower resolution, I think the CupCake has the potential to print ABS better than the Prusa.

And man, is that 0.6-mm nozzle fast compared to a 0.4-mm nozzle. With about twice the cross-sectional area, one could expect the CupCake to print almost twice as fast as the Prusa, again at a lower resolution — and at the same time that the Prusa is busy printing something in PLA. Preliminary slicing with the CupCake profile I’ve built in PrusaSlicer bears that out.

So I have a few plans up my sleeve, and you should be seeing more soon.

That said, this update is a bit reminiscent of “I got a web browser running on a Commodore 64!” Fascinating as a bit of retro archeology, but when you can now buy a budget 3D printer for under ~$200 that will reliably turn out quality prints out of the box, I question whether it is worth the effort to bring a zeroth generation CupCake into the modern era.

But if that’s what it takes to bring your blog back to life, I welcome it.