Akila's week 12 at Fab academy

1. The circuit design is based on Neil's circuit in the course webpage. I have added a switch and changed the pin header to connect the motor from 2x2 to 1x4.

2. I autorouted the circuit (with the usual design rules: Clearances=16mil; Minimum width=18mil) first, followed by manually increasing the trace width to 30-40mil to handle the 12V motor.

3. The traces to be milled.

4. The PCB outline to be cut and four holes to be drilled for two jumper wire connections.

2. PCB production

1. The tool path for the traces to be milled in the PCB using the 1/64in tool bit.

2. The toolpath for the PCB outline to be cut with the 1/32in tool bit.

3. The machine bed was not totally flat. Hence the traces were not milled completely on one half of the PCB.

4. I increased the Z-depth and tried milling along the same toolpath again. This time, since the tool used was a V-bit, it cut off perfectly on left half but took away too much copper from the right half of the PCB.

5. The traces on the right half of the board are too thin and hence may peel off when heated. I decided to mill another board.

6. The board that I milled again was better but not the best. Probably because of a mediocre tool bit used. The holes were not drilled fully and I drilled them manually through using a broken tool bit. I had to cut off some copper to accomodate the 1x4 pin header to connect the motor.

3. PCB programming

A few datasheets that I referred to understand the working of the bipolar stepper motor : source1,source2, source3.

After checking if the board is fine with avrdude command, I flashed Neil's stepper motor code into the ATtiny44. The clockwise rotations looked fine (see video at the top of this page) but the anti-clockwise rotations did not.
I tried Rahul's code. The steps worked.
I then wanted to programme switch control of the motor. I tried this in Arduino IDE. I modified a code logic from an internet source to incorporate switch control. Frustratingly though, the switch worked only to pause the motor when the pin is held high in the code and switching would cut off the current. The other way where the pin is held low and switching would take it high and thus operate the motor, did not work. This is a puzzle yet to be solved. The code, however, worked beautifully for clockwise and anticlockwise rotations: ino file

Something else that I would like to document is my persisting problem with soldering. On two days, I was stuck with only one motor driver chip heating up and the other one idling. On each of those times, it was either one or the other chip not soldered properly. A lot of time wasted in debugging. Soldering is still my weakness.

A figure from the internet that I used to understand and implement the coding logic. I am yet to study and understand full step (one/two phase), half-step excitation, microstepping etc.

For the 4x1 pin header to connect to the motor, I had to design carefully, referring to which wires in the motor were coil pairs. One pair of coil terminals had to be connected to pins of the same motor driver chip. The other pair had to be controlled by the other driver chip.

The makefile executed. The board is working fine.

Jumper wires on the left to connect to the power supply. Jumper wires (yellow and red) on the right end of the board to complete the circuit routing.

Using 12V and 0.5A power supply to operate the motor.

Flashing different codes into the chip to check the motor control.

Week 12 - Output devices

1. PCB design

2. PCB production

3. PCB programming

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