I've taken a second look at my old BLDC stroboscope project
, prompted by requests by other forum users, most recently Georg in this thread
The original software as well as schematics left a lot to be desired. One of my own problems with it was the dangerous overheating of the SN754410 chip used as the H-bridge(s). The circuit only allowed for driving the winding with high or low levels and this is not a very efficient way of doing it since on each step there's one winding that's working against the force of the other two.
Anyway, given that two users have already reported that they cannot make the original software work, I decided to completely abandon both the circuit as well as the software and create them anew with potential for making an actually usable sensor-less ESC (Electronic Speed Control) for small BLDC motors, such as those used as the spindle motor in DVD drives.
I'm still playing with the circuit and the software is a b**ch given the issues with back-EMF on small RPMs which is what I was interested with. Perhaps I will eventually give up on the sensor-less approach but for now I can at least make the motor run in a good (for me) range of RPMs between 0 and about 1100RPM and I'm playing with various settings for the spin-up routine as well as software PWM.
Anyhow, although the actual ESC is not ready yet, I already have a circuit as well as software that could be used for a more stable stroboscope project. Please see the attachments below for the diagram and the Arduino sketch.
Please note that I based my new circuit on discrete transistors (three pairs of complimentary PNP-NPN transistors) but it should in theory work with SN754410 H-Bridge ICs as well. In fact, other users already reported it working with the equivalent L293 chip, so you should be fine with SN754410 as well. Just use the Arduino's digital outputs 9,10 and 11 which on my digram go to their respective transistors H-bridges to activate the corresponding inputs of the L293 or SN754410 chip.
Please note also that this software is not using PWM (for speed of development I took it out) and so the DVD disk freely laying ontop of the BLDC spindle may slip (the spindle rotates in steps, not continuously as with PWM), so you may want to either use laptop DVD drive motor that has three little latches for the disk or, like I'm doing here, just lay two disks one ontop of another to weight it more and create more friction - that will take the choppiness of the rotation out.
Please post here if you've successfully built a stroboscope using this circuit / software and if you have any questions at all about this project, post them in this thread.