This is an _old style_ stepper driver thought to be used with the popular _28BYJ-48_ Stepper Motor. I created this circuit for using it in conjunction with the Rotating Table by Basement Creations

Times ago a couple of friends 3D-printed that Rotating Table and built a stepper driver using an Arduino. When they published pictures of their work on social networks, some people complained about that saying things like:  

This can be achieved using an NE555 too! Why waste a microcontroller?  

Yes, I said, but that can be done using also 4 pushbuttons and putting a trained monkey in front of them that pushes buttons one at time sequentially... But I did't read comment like this, very strange IMHO. It's clear that every task can be fullfilled in a lot of different ways but there is always someone ready to criticize because looks like we humans are made for this.

Anyway, since I had a lot of ancient ICs in my drawers (one of my hobbies is to repair vintage stuff) and I wanted to refresh some old electronics I learned during my school years, I made the stepper controller using an NE555, a decade counter and a darlington array IC. Now the remaining part of people can say stuff like:

Why use so old components? They're fuc*ing expensive nowadays! An ATmega328 would be more cheap!  

Making all people happy to criticize every other's project. So, first than criticize, please let me see your trained monkey device. 

How it Works

An NE555 is configured as Astable Oscillator : this means the expensive NE555 will produce a square wave continuously. In this configuration frequency is determined by R1, R2 and C1 in the schematic. I keep fixed C1 at 100nF and R1 at 10K so you can vary frequency by varying R2. For R2 I used a 10K resistor in series to a 100K trimmer. Since frequency of astable oscillator is determined by formula:  

f=1.44/((R1 + 2*R2)*C1)

when trimmer is set to zero, R2=10K and then frequency is 480Hz (motor at maximum speed), then trimmer is all turned R2=110K and then frequency=62Hz.

I designed the PCB so you can use a trimmer mounted on PCB (VR1) OR an external potentiometer to be mounted on panel and attached to VR1E connector : only one of those 2 must be used.  

Frequency output from NE555 is sent to a 4017 decade counter for generating pulse waves for driving the 4 coils of the stepper motor from outputs 0,1,2,3. Output 4 is sent to reset input for making cycle start again. 4017 outputs are connected to an ULN2003 for the power driving. Usually you can obtain a small board with an ULN2003 together that motor when you buy it: from that board you can recover the IC, the IC socket and the motor connector.

More info in the Github repository