Stepper Motor Driver, For Testing
3d solderingWhat is the purpose of this? Testing stepper motors: the circuit generates a blinking signal. The (purple PCB) driver then gets that blinking on its step pin.
The idea is to connect a stepper motor to the driver, and the driver should start making the motor turn, thanks to the blinking signal fed to it. I just had some fun making the blinking part 3d soldered!
As a simple testing setup, the direction pin is just shorted to ground and the step pin has some constant frequency signal with the intention of making the motor spin fast. Because it’s just for testing I don’t care about which frequency exactly, but it should be a simple circuit.
Online I found schematics for a blinking circuit with very few and cheap components, so then it was time for soldering! 3D soldering even
First working prototype, 3D soldered but it has some superfluous components, to figure out the best values. I’m not happy with how it looks
With redone 3D soldering: it allows a very efficient use of volume around the PCB. Also the “traces” can cross over each other just in the air.
On the right you may note the connector: yes it’s a pin solder-on header, as the connector to the motors’s coils. If it works, is it stupid?… Just don’t drop a screwdriver on it!
Side view
Bill of Materials #
- transistor BC547
- green LED 5mm
- capacitor 100nF
- resistors 6K8, 1K, 300, 150
On the pictures you may note I use two 150 resistors in series for the 300.
Schematic #
The blinking part is sometimes sensitive to outside EM noise, especially on the base pin.
The SLP and RST pins need to be pulled high for the driver to be happy, so that’s just a voltage divider. Then, the blinking part works with something “negative resistance” of the tansistor (note it’s connected flipped) which I don’t understand, but it works!
On the STP pin we then have an oscillation that tells the driver to turn the motor by one step every time, all without a microcontroller or a 555 timer.
Well, the oscillation can also be achieved with a “classical” two-transistor blinking circuit but this thing works with just one…
About these negative resistance characteristics of transistors, there’s also this and some, explainers.