I'm prototyping a concept and for now will happily use a module (TMC2208) to operate a mechanical sub assembly that uses tiny bipolar stepper motors. There are three of these sub assemblies and there's (A) no great reason to ever use them simultaneously. I also (B) can't really think of a great reason they'd ever need to turn backwards.
With those general parameters I'd still like to be informed for some future conversation where we start to discuss and source for production- likely a custom PCB circuit. I'm also just curious about what the minimum circuit IC would look like.
Given parameter A: Would there even be a need to use 3 driver ICs, or would an EE typically use the same driver to sequentially control each assembly?
Given parameter B: Would I even need a driver at all (or an H-bridge?), or would you just use a transistor scheme?
Steppers don't hold position if power is not applied.
Given parameter B: Would I even need a driver at all
An H-bridge of some sort is always needed, because to take a full step, the current through one coil has to be reversed. The only difference between forward and backward rotation is the order of the current reversal.
Ok, thanks! for parameter A: That's ok. There is friction in the system to hold them in place regardless so I'd happily turn them off and save power.
Parameter B: Ok. Fair enough. You may have seen an earlier post about driver choice for this project. It would still be nice to reduce # of wires for the microcontroller, and to that end, I can at least collectively ground the direction pins here, but overall I guess we'll still need at least one driver (H-bridge) circuit.
It's actually the little sub assemblies that inspired this concept from the get go- given how little we're leveraging the precision step and directional ability, I'm kind of surprised they use stepers at all (over a basic coreless DC to keep it simpler), but for the cost and size, I'm envisioning the same assmeblies in a production item- everything else could change.
I dunno. Ask you I guess.
Could be that's a terrible idea. Maybe they just use individual driver chips, maybe theres one chip that contains multiple H-bridges for a stepper array. I'm here because I'm curious.
Multiplexing one driver to three steppers is totally unrealistic.
Three of the TMC2208 would be a fine choice. Control logic voltage is 3.3 to 5V, and only one control wire is required for per motor, using the UART serial option.
Ah, ok, so that was Sarcasm. Cool.
I did see someone else wondering the same thing recently, so it was unresolved in my head- I tend to think of things more mechanically so imagining this somewhat like an old timey phone switchboard I can see it. I didn't know if there was some analogous design strategy in PCB design.
Part of my curiousity here is to start visualizing cost- multiple little steppers like this are pretty common these days (cameras, etc.) and TMC2208 seems to cost a bit more than average. I thought some IC manufacturer might be selling a chip designed to run an assortment of identical spec steppers and offer cost savings.
It's nothing that I need to worry about right now, but I'm always interested in being at least somewhat prepared if/when that topic comes up.
Any of those was the motivation. Your second sentence sums up my answer. I was just wondering. The higher cost of TMC2208 over other contenders is what prompted the thought- that and just wondering about the production solution.