Example Application

5 of 5

Figure 4. Manual Control of a Stepper Motor

Figure 4 shows the ELM310 used in a circuit to

control a four phase stepper motor. The motor shown

here is typical of the type often found in computer disk

drives, and are readily available on the surplus market.

This particular motor requires +12V at 160mA per phase

to operate, and has a resolution of 3.6° per step.

Momentary action pushbuttons are used as control

inputs in this case. This allows the user to experiment

with the operation of the motor. An ELM410 is used to

debounce

the

switches,

so

that

the

mechanical

bouncing of the switches does not cause multiple steps

of the motor armature.

Both integrated circuits are powered from a 5 volt

supply, not shown on this diagram. This supply could be

derived from the 12V for the motor, but is not

necessarily, as the user may want to separate the two

due to noise from the motor.

The motor is directly driven by IRF511 power

MOSFETS in this design, because they were readily

available, but many other devices would be suitable.

The main criteria, as well as voltage and current

capabilities, is that the MOSFET be fully switched by the

logic signal available (in this case 5V). Some of the

‘logic level’ HEXFETs would be well suited in this case

(IRLZ14 or IRL510 for example).

The main advantages of power MOSFETs over

bipolar types are their ability to be driven directly from

CMOS logic, and their inherent reverse biased diode

ELM310

ELM310DSB

2

3

4

6

5

+5V

8

1

0.1µF

+5V

Step

Clockwise

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

1

2

3

4

8

7

6

5

Bk

R

G

Br

W

+12V

*

*

*

connected from Drain to Source internally. This diode

helps to control inductive kick-back when a winding is de-

energized. Optional resistors (50-100

Ω) are shown in the

circuit to dampen resonances due to wiring inductance

and gate capacitance. They should be used if the

transistors are mounted any more than a few inches from

the ELM310.

Operation of the circuit is straight-forward. The motor

advances one step each time the step button is released.

If the clockwise input is also pressed, the windings will be

energized in the order A-B-C-D when in full-step mode,

and A-AB-B-BC-C-CD-D-DA in the half-step mode.

Recall that when power is first applied, no winding is

energized, to provide a means to sequence the start-up

of several motors in larger systems. For this reason, no

output will appear until the first step command is issued.

This circuit demonstrates the operation of a stepper

motor,

and

can

easily

be

modified

for

further

experimentation. One change that could be made is the

addition of an oscillator in the place of the ELM410, to

provide continuous motion. Another might be the direct

connection of the ELM310 to a computer port for

robotics, and the incorporation of sensors for feedback to

the computer.

*

Stepper

Motor

7