Control a stepper motor with just one low cost IC

There are generally two type of motor that can do the amount of work you request, stepper and a servo motor. Stepper is usually more precise but slow (to prevent overturn or underturn), but those stepper in your hardrive is not slow at all, it can even go up to 10'000RPM, perhap it turn a large degree for every driving signal? Or it can be magnetized/demagnetized very fast, I just never have experience with it.

A stepper motor is the type of motor that usually use in printer, typewriter to roll the paper in the correct length one time a bit.

Custom stepper motor driver is expansive, usually around RM15 to RM25 each driver IC. If you burn one during development of your project, that mean you burn RM15 each time.

Alternatively, you can use 4 MOSFET or BJT and one microcontroller to drive your unipolar type stepper motor. If you need to drive a bipolar type stepper motor with only 4-pin as you found on most printer, you will need at least 6 transistor to form two individual switchable H-bridge.

A H-bridge is a transistor bridge that allow bipolar (two direction) current flowing. To cut the cost, one can actually get a ready available bidirectional motor drive IC on the market such as BA6238A.

Those IC are very famous last time, it is widely use in CD-player, tape-recorder and etch. As long as there are at least 2 bidirectional channel, you can use it to drive a stepper motor. Please note that those IC only cost less than RM3, but I doubt will you still get it from the market as it is obsoleted. Nowaday BJT is widely replace by the MOSFET due to it significant power saving benefit over BJT.

You can refer to code below to drive your BA6238A to bipolar stepper motor, please note that a unipolar stepper can be drive with bipolar driver, but a bipolar stepper motor won't work if drive with unipolar driver.

Last Pattern is global variable that store the last motor control patern. We only need to output 3 LSB pin from PC port or MCU port to the BA6238A. Pin 10 of BA6238 is common to both bipolar coil of the motor, Pin 2,3 is connected to the repective coil of different phase.

ACT_OP1=0x07; //Motor 1 mask 00000111, last 3 pin of port B
if (MTP1.Val>RELATIVE_POS1.Val && !FORCE_REVERSE)
{
switch (LAST_PATTERN1)
{
case 5: LAST_PATTERN1=3;break;
case 3: LAST_PATTERN1=4;break;
case 4: LAST_PATTERN1=2;break;
case 2: LAST_PATTERN1=5;break;
default: LAST_PATTERN1=5;
}
RELATIVE_POS1.Val++; //Change this to change direction??
}

Reverse drection is done with reversed pattern.

else if (FORCE_REVERSE)
{ //MASK=LAST_PATTERN1 & 0x07
switch (LAST_PATTERN1)
{
case 5: LAST_PATTERN1=2;break;
case 3: LAST_PATTERN1=5;break;
case 4: LAST_PATTERN1=3;break;
case 2: LAST_PATTERN1=4;break;
default: LAST_PATTERN1=5; }
RELATIVE_POS1.Val--;
}
else
{
ACT_OP1=0;
}

motor= LAST_PATTERN1 & ACT_OP1

'motor' is Port B in my case. I know it is dificuit with no photo here, but I am not too free to take the photo yet, will try to post it later if posible.

Please note that you should turn the active coil off for a while before you turn on another coil, you can do this with timer, alternatively, a current sense circuit can be used to sense the current across the motor. The best way is high side current sensing on BA driver, then chop the supply off when it over the limit. If you sense it at low side, the digital i/o signal will become too noisy.

Ok, I think that is enough for small piece of information, if you have problem kindly email to: mail.altbattery@gmail.com. May not be replied on this affair, but you can try your luck.