Following, i designed and made the PCB for the sugar and coffee dispensers. For this controller, i will use a doubled Unipolar Stepper Motor Full Step Controller that i had designed a couple of days ago. Because i have to control 2 motors, i will design one controoler and i will also include 2 relays to select each time which motor to drive. Of course, both motors will be able to run simultaneously.

So, here is the schematic diagram of the circuit:

The X1 connector is for the power supply. The SV1 is the interface to the main board, which will ultimately control all the modules. I use 2 relays, K1 and K2, to connect or disconnect the common wire of the motors. The relays will be controlled from the main board directly. Into production now:

The procedure is more or less known. First, the printout of the PCB	Then i cut the transparencies into size.	And i also cut a photosensitive PCB board to size...	...Which i smoothed its edges with a file

Transferring the artwork to the PCB with photographic method	Developing the PCB in the solution	Drilling a hole for hanging the PCB into the etching bath	And finally, etching the PCB

After cleaning and drying the PCB...

First the drilling part.	And then,the soldering part	BTW: My soldering station rocks!

This phenomenon worths to be mentioned. When i put the controller into test, it worked perfectly, except one slight problem: No matter which motor was enabled (by the relay), both motors would run! I could not run a single motor by no means! Then, i re-checked the circuit and found out what happened!:

Suppose that K1 is closed and K2 is open. The top motor should operate, while the bottom should be stopped. Now, suppose that a pulse arrives at the gate of Q2. The red line, indicates the normal current flow, through the top motor and through the Q2. The blue line, indicates the parasitic current flow. From the other side of the first coil of the top motor, an amount of current runs through, and goes through the other motor's coil! That is exactly why both motors run, even if the second motor's common wire is completely disconnected!

To resolve the problem, i soldered diodes on each of the 4 wires of the coils:

This way, the current will not follow the blue line, as it cannot go backwards to the second motor's coil. I soldered the diodes directly on the wires of the motors, because i did not want to re-make the PCB:

8 diodes and 8 pieces of heatshrink tube is what i will need	I cut the leads of the diodes small	And one by one, i cut the wires of the coils of the motors. NOT the common wire
Then i soldered the diodes with the correct polarity	And with the thermal gun, i shrink the heatshrinks	Done this for both modules

And then i tested the modules. they work perfectly! Now i can control both motors with a single controller, being also able to run them simultaneously.

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