Hello,

I opened up a working cd-rom drive that has a BD7907FS chip which drives the spindle motor, loading tray motor and sled(laser) motor. I'm only interested in the sled motor portion since I'm looking to drive the stepper motor (worm gear motor) separately for another project using (hopefully) an Arduino.

Here is the Datasheet:
http://pdf.datasheetcatalog.com/datasheet/rohm/bd7907fs.pdf

From what I could make out on my own it seems the upper right hand portion from pins 28-37 is everything that has anything to do with the stepper motor. it seems pins 28, 29(Sledin1/2) is the input for the stepper motor.

Also the stepper motor is a bipolar 4 wire motor with 2 windings, each ~10.7 ohms and it has a long worm drive gear as it's output.

I've tried (blindly) applying +5v and GND to the two input pins and reversing it (all while the cd-rom was plugged in to a computer power supply) thinking that was the signals that it took to drive the motor, but I had no luck.

I know that a bipolar stepper motor requires switching polarity on each winding in the correct pattern and fast enought to make it well, step or run. I know I can easily make this setup go using an H-Bridge like the L239D from TI, but I would like to use what I have at hand.

So, I'm wondering if anyone can help me decipher the datasheet and help me run my stepper motor with that IC. What needs to be connected to what and what inputs are needed to driver the motor?

TL;DR Help me run a 4 wire stepper motor using this IC: http://pdf.datasheetcatalog.com/datasheet/rohm/bd7907fs.pdf

 

It looks like at best all you will get with that chip is to run the motor in 1 direction or the other. The circuitry that drives the stepper moter phases is all internal ans my hunch is that 1 pin runs the motor in 1 direction and the other pin makes it go in the other direction. Something that isn't obvious needs to make the motor only run for so long (to move the sled in or out)
The data sheet doesn't really indicate what level makes the motors go, 5v is a good guess. Have you isolated the two sled pins from the cd player controller?

 

Quote, " it seems pins 28, 29(Sledin1/2) is the input for the stepper motor." The section of the chip you are using for the driver looks to be the H-bridge. The pins #28, #29, look to be expecting the pulses that would drive the motor. Thes pulses would come from your Arduino. You need a stepper program for the Arduino to drive those pins in the correct sequence.

 

2)ON/OFF for each driver, brake mode switching of spindle and stand-by mode switching can be controlled by 2-wire serial data

Reverse engineering stuff is the best learning experience.

You really want to logic probe the inputs of interest while in operation unless that is not possible.

Are there ON/OFF brake standby signals involved? That is what the quote above indicates.

After that is cleared up you should be able to give the correct pattern of on off to the stepper PWM input pins.

The sequence of controls signals for 2 control wires is as follows
(columns C1 and C2 from above):

Step C0 C1
1 0 1
2 1 1
3 1 0
4 0 0

Reverse direction through the pattern will spin the other direction.