Week 3: January 30 to February 5, 2012

Hardware Development & Testing

I received part of the components from farnell on 30^th January while the balance arrived on 2^nd February 2012. 

1st delivery

2nd delivery

Therefore, on 31^st January I started to construct and test the motor driver with the stepper motor by using digital trainer as the input. However it didn’t work out. The stepper motor did not move at all. Then I tried to test the stepper motor directly with digital trainer. After a few attempts the stepper motor works.  This is the sequence that I used to test the stepper motor. For every 2 steps, the motor will move once. This is called two phase full driving. During this testing, the motor moved at step 1 and 3.

Step	White/Black	Blue	Yellow	Orange	Red
1	+3V	1	1	0	0
2	+3V	0	1	1	0
3	+3V	0	0	1	1
4	+3V	1	0	0	1

Testing process

The motor driver circuit

The motor

Since the motor driver did not working, I measured the voltage at the input and output of the motor driver and find out that the output voltage is different from the input. 

Input		Output
A	4.98V	A (Blue)	3.0V
A/	4.98V	A/ (Yellow)	3.0V
B	4.98V	B (Orange)	3.0V
B/	4.98V	B/ (Red)	3.0V

Basically, the input and output voltage should have the same value as this driver main function is to increase the current to drive the stepper motor. However, in this case the output voltage had the same value with the voltage supplied to the centre tap of the stepper motor (white and black wire). Why? I’m not sure. So I did searching for another schematic using SLA 7024 to compare with schematic that I used and I found one with exactly the same connection but with slightly different value.  Perhaps the motor did not work with digital trainer logic (I used 8 bits data switches as the input). As I went through the datasheet, it says “HIGH CURRENT PWM”,”DUAL PWM CURRENT CONTROL”. Perhaps this driver has to be triggered from a microcontroller. So, I decided to test the driver directly with microprocessor. Therefore I have to develop some code, probably the motor sequence to test the functionality of the driver.