Electronics > Beginners
Manual Stepper Motor Control (No Arduino)
Sikorsky66:
Im Building something called a "Barn Door Star Tracker" but that's not really important, its basically just a clock you slap your camera on.
For this project I'm going to need a stepper motor but with very simple functionality,
basically just a way to set a constant rpm and to do it as cheaply as possible,
and then power the whole thing with a simple USB 5v 2.0A power bank.
I was thinking of using a 28BYJ-48 stepper motor, they're cheap and 5v
Some kind of cheap stepper driver, most of the cheap ones seem to be tailored towards Arduinos which is annoying in my case
(this is the part that's giving me a hard time as i just don't know enough about how these work)
And finally some kind of PWM signal generator,
with a 5v +- input, a screen displaying the frequency, some buttons/knob to adjust the frequency and a pwm/grnd output.
These seem to be fairly cheap and common.
Could I please get some help finding the right stepper driver and some guidance on how to wire this all together.
Thank you
brucehoult:
The drivers aren't really anything to do with Arduinos -- they are generally simply a kind of current amplifier to get enough power to drive the stepper.
This type of stepper is a "unipolar" one which means it has a "common" wire and four phase wires. You connect common to ground (for example) and then connect each of phases 1, 2, 3, 4 in order (or in reverse order) to 5 V.
You could use anything you want to generate the pulses. For example a 4 bit bidirectional shift register (you'd have to somehow get one bit set one at power up). Or a two bit up/down counter, followed by a 2-to-4 decoder.
But I can't see any good reason *not* to use a cheap microcontroller or microcontroller board -- they're available for $5 or even less.
Note: bigger stepper motors are usually "bipolar" and need a more complicated bridge driver board which uses two pairs or wires A and B and generates first voltage one way and then voltage the other way on each pair. If you happen to get this type of driver I've found you can use it with a unipolar stepper motor by simply leaving the common wire unconnected.
Ian.M:
Many stepper motor driver ICs do a lot more than provide a high current output stage per coil or coil end as Bruce just described. Its common to have pulse and direction inputs, where pulse causes it to step once on each activation, and direction is a logic level that chooses whether the step is forward or backwards. Also, for a star tracker, you only need a fixed speed in tracking mode, with that speed determined by the mount's gearing, so you can calculate the exact pulse rate required and generate it in pure dumb logic by dividing down the output of a crystal oscillator, to whatever accuracy you require.
However, as has been pointed out, that would be actually the *HARD* way compared to using an Arduino clone*, and a stepper driver shield. That would also let you compensate for the tangent error of the mount electronically, for optimum tracking accuracy over the full mechanical movement range.
If you need a menu interface, add an I2C LCD and button shield, but the application is simple enough that once the speed is worked out, all the user interface you need would be a stop/run switch and a status LED.
Also most USB powerbanks shut down at low load currents, so you may well need to use a LiPO with a separate 5V output boost board.
* Genuine Arduinos use a ceramic resonator for the ATmega clock. The accuracy and thermal stability is poor compared to a crystal, so in timekeeping applications that don't justify the use of external RTC, a clone that uses a 16MHz crystal rather than a resonator is preferable.
rstofer:
Considering that the Internet is FULL of Arduino Barn Door Tracker projects, you probably don't need to know much about how to code the project. Copy, paste and 'click' the Upload button and it's all done.
A Google search will find a lot of these projects.
Refrigerator:
Stepper drivers are super simple. Direction pin is to set direction and Step pin is to take a step in said direction.
There are also microstepping and other pins but you can leave those disconnected and the driver will work in default mode, stepper drivers work fine at 5V.
28BYJ-48 will not work with regular stepper drivers because is has a common connection in the center tap of both coils, so you need to pop the blue cover and cut a trace inside the motor to make it work.
Or you can also do it with transistors >:D
Since 28BYJ-48 steppers have a common wire you could in theory control them with a two transistor miltivibrator.
Three coil wires to one transistor and one wire to the other, this way it would rotate on it's own and not buzz, sort of like a shaded pole induction motor.
For smoother operation you can do the controls with a transistor ring counter. To get 4 steps for a full revolution you would need 8 transistors and two more for a multivibrator, as i've found they're the most stability you can get with two transistors. But these discrete transistor drivers would be non reversible.
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