Stepper Motor Logic Circuit

This stepper motor logic circuit uses a 4017 decade counter IC to produce the necessary logic for the driver circuit, shown in the previous page of this multipage article. This circuit makes use of counts 0 to 3, and on the fourth count, it resets and begins again. You can see that pin 10, which produces an output on the count of four, connects to pin 15, which activates RESET.

As you can see from the animated circuit diagram, each output from the counter has to drive a pair of coils; therefore, we are using diodes to prevent the output current from one pin sinking into another pin. For this application, I am using the 1N914 diodes simply because they are cheap to buy in bags of 100. You could use the 1N4148 if you already have them.

This circuit also requires a slow clock pulse through pin 14. I have designed a variable frequency square wave generator using a 555 IC for this part. I decided to use this IC because I wanted to keep it within scope of GCSE students. This circuit, and others, are in the following pages of this article.

Logic Sequence

As well as being an extremely simple circuit to make, the 4017 IC is extremely cheap to buy and I managed to get a bag of 100 for around three pounds from online auction sites.

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