9

FORGE

Now, flash the code, from hsmag.cc/lwNQKt, to
your Arduino and if everything goes according to plan,
your motor should rotate alternately 360° clockwise,
then 360° anti-clockwise, with 0.5 second pauses,
until you remove the power. Now, let’s take a closer
look at what’s going on.

CODE CLOSE-UP

const int step_pin = 5;

const int direction_pin = 4;

int delay_time = 500;

Lines 1–2 of the code above set the values of
the ‘step’ and ‘direction’ pins we’re using. Then the
last line of code sets the delay time (in microseconds)
between steps. 50 μs gives maximum motor speed
of ~10 000 steps per second or, to put it another
way, ~180 rpm. It doesn’t work well if you try to go
faster. If you need faster rotation, consider using
fewer microsteps (see the data sheet at hsmag.cc/
nYKMEQ). At the slow end, 5000 μs works perfectly
well too, giving a very usable range.

digitalWrite(direction_pin, HIGH);

for(int x = 0; x < 3200; x++) {

digitalWrite(step_pin, HIGH);

delayMicroseconds(delay_time);

digitalWrite(step_pin, LOW);

delayMicroseconds(delay_time);

}

Looking closer at the code above, the line
digitalWrite(direction_pin, HIGH); sets the

motor rotation clockwise – LOW would be used to set it

to anti-clockwise.

The code then loops 3200 times to generate – you

guessed it – 3200 HIGH/LOW pulses to the step pin.

Each complete HIGH/LOW cycle signals the A4988 to

perform a step. There is a short delay of delay_time μs

between each HIGH or LOW, so each step takes two

times delay_time μs.

Which all means that you set the motor direction

by driving direction_pin HIGH or LOW, and the motor

speed by adjusting the value of delay_time, and the

number of steps by writing pulses to

step_pin. Now you can incorporate either kind of

stepper motor into your projects and, well, take over

the world. Happy making!

SETTING THE

Once your circuit is wired up, you’ll need to set the

value of Vref using the potentiometer.

Examine sense resistors (Rs) marked S1 and S2.

The example board has R100.

Look up the value on hsmag.cc/DlkyOH

R100 = 0.100 Ω

Look up the maximum current rating of your

stepper motor. 17HS08-1004S = 1 A

Now use the equation...

Itripmax * 8Rs = Vref

In this case, Itripmax = 1 A and Rs = 0.100 Ω

So Vref = 1 * 8 * 0.1 = 0.8 V

Now power up your board and motor and adjust

the potentiometer until the voltage between its metal

top and GND equals 0.8 V (or whatever you calculated

if your values are different). This will set the motor

current limit at 1 A.

A4988 CURRENT LIMIT

Arduino Nano powered by USB. Motor

powered by >8 V supply.

3 × 12 kΩ resistors used to ensure 1/16

micro-stepping resolution.

100 μF electrolytic capacitor.

Blue, red, black, green motor wire

colours match those of my motor.

The full code for

these stepper motor

projects can be

found on GitHub:

hsmag.cc/BiqFPe

QUICK TIP

Figure 3

Wiring the NEMA 17

17HS08-1004S is a

bit more involved, but

isn’t difficult if you are

methodical and take

your time

Left

Wiring for the unipolar

28BYJ-48 circuit (left)

is very simple. The

bipolar NEMA 17

17HS08-1004S (right)

is a bit more complex,

and requires separate

motor power