Hi all,
I'm trying to make this long post a little easier to read, and this is the only way I know how. So I apologize if this looks too much like a school report.
What I'm trying to do:
As part of my final year college project, I am trying to build a driver circuit to drive my magnetorquer (Think of it as a solenoid within a metal coil) , the magnetorquer is : http://www.cubespace.co.za/cubetorquer . I intend to supply bi-directional current to it using a H-bridge motor driver, the motor driver chip that I am using is : http://www.mouser.com/ds/2/427/sip2100-519775.pdf
I will be controlling the input pins (InA and InB) using PWM signals from my arduino. As a test, I am just using a simple arduino program that varies the duty cycle of the pwm output in Pin 5, and sets Pin 6 to digital low. The connection of my circuit is the attached image. Note that the batteries would represent my DC Supply(I am using 5V to power my chip) , and the inductor represents my magnetorquer. Also, assume that the bottom left pin of the IC is pin 1.
What went wrong:
I have observed that as I am drawing an unusually low amount of current, compared to what I should get theoretically(V=IR , resistance of the magnetorquer is shown in the link above ). When the duty cycle of my PWM signal is set to 50%, the chip only draws 0.030A of current, in that case the resistor of my magnetorquer would be R=V/I = 2.5/0.03 = 83.33Ω! Which is almost thrice of what is stated in the link above!
I am using an oscilloscope to measure the output voltage across my magnetorquer, when I set my duty cycle to 50%, what I get on the oscilloscope is a square wave that has max and min voltages of 2.5V and -2.5V respectively. If Pin 5(OUTB) of my motor driver is always 0, I should expect to see my output voltage vary from 0-2.5V right?
Also, when I set the duty cycle to 100%, I should be expecting to see 5V on my oscilloscope, but what I see is a very small DC voltage ( about 100mV ) which is effectively 0.
What I've tried:
I tried connected the negative end of my magnetorquer to ground while keeping the positive end at Pin 8 (OUTA) of my motor driver chip, but nothing changed.
I have tried shorting Pin 5(OUTB) of my motor driver chip to ground, didn't work either.
I have also tried connecting a the second channel of my DC power supply ( Set to 2.5V ) to pins 6 and 7 (InB and InA ) of my motor driver chip, when I do this the current jumps up to about 0.150A and doesn't increase when I increase the supply voltage of the second channel of my DC power supply.
I'm currently really out of options, at this point I can really only assume that my motor driver chip is broken. Is there something that I am not doing right?
Thanks and sorry for the long post.
I'm trying to make this long post a little easier to read, and this is the only way I know how. So I apologize if this looks too much like a school report.
What I'm trying to do:
As part of my final year college project, I am trying to build a driver circuit to drive my magnetorquer (Think of it as a solenoid within a metal coil) , the magnetorquer is : http://www.cubespace.co.za/cubetorquer . I intend to supply bi-directional current to it using a H-bridge motor driver, the motor driver chip that I am using is : http://www.mouser.com/ds/2/427/sip2100-519775.pdf
I will be controlling the input pins (InA and InB) using PWM signals from my arduino. As a test, I am just using a simple arduino program that varies the duty cycle of the pwm output in Pin 5, and sets Pin 6 to digital low. The connection of my circuit is the attached image. Note that the batteries would represent my DC Supply(I am using 5V to power my chip) , and the inductor represents my magnetorquer. Also, assume that the bottom left pin of the IC is pin 1.
What went wrong:
I have observed that as I am drawing an unusually low amount of current, compared to what I should get theoretically(V=IR , resistance of the magnetorquer is shown in the link above ). When the duty cycle of my PWM signal is set to 50%, the chip only draws 0.030A of current, in that case the resistor of my magnetorquer would be R=V/I = 2.5/0.03 = 83.33Ω! Which is almost thrice of what is stated in the link above!
I am using an oscilloscope to measure the output voltage across my magnetorquer, when I set my duty cycle to 50%, what I get on the oscilloscope is a square wave that has max and min voltages of 2.5V and -2.5V respectively. If Pin 5(OUTB) of my motor driver is always 0, I should expect to see my output voltage vary from 0-2.5V right?
Also, when I set the duty cycle to 100%, I should be expecting to see 5V on my oscilloscope, but what I see is a very small DC voltage ( about 100mV ) which is effectively 0.
What I've tried:
I tried connected the negative end of my magnetorquer to ground while keeping the positive end at Pin 8 (OUTA) of my motor driver chip, but nothing changed.
I have tried shorting Pin 5(OUTB) of my motor driver chip to ground, didn't work either.
I have also tried connecting a the second channel of my DC power supply ( Set to 2.5V ) to pins 6 and 7 (InB and InA ) of my motor driver chip, when I do this the current jumps up to about 0.150A and doesn't increase when I increase the supply voltage of the second channel of my DC power supply.
I'm currently really out of options, at this point I can really only assume that my motor driver chip is broken. Is there something that I am not doing right?
Thanks and sorry for the long post.
Why? That may have fried the chip, or if you're lucky the chip's internal protection will have saved it.
