What is a Stepper Motor Driver?
A stepper motor driver (or stepper motor drive) is a circuit used to drive or run a stepper motor. A stepper motor driver usually consists of a controller, a driver, and the stepper motor’s connections.
A lot of driver circuits are available on the market today.
Over time, these have been made to be easier and easier to interface to a stepper motor.
You can almost instantly run the motor as soon as you connect the driver circuits to it.
These circuits come in current and voltage ratings, so it’s important that you select the right driver circuit according to the motor’s ratings.
Essential Components of Stepper Motor Drive
- Controller (essentially a microcontroller or a microprocessor)
- A driver IC to handle the motor current
- A power supply unit
Stepper Motor Controller
The selection of a controller is the first step to building a driver. It must have a minimum of 4 output pins for the stepper. Additionally, it must contain timers, ADC, serial port, etc. depending on the application in which the driver will be used.
Stepper Motor Driver
Nowadays, people are moving away from discrete driver components like transistors to more compact integrated IC’s.
These driver IC’s are available at reasonable costs and are easier to implement in assembling, which improves the circuit’s overall design time.
The drivers must be selected to suit the motor ratings in terms of current and voltages. ULN2003 series of drivers are most popular in non-H Bridge-based applications, apt for a stepper motor drive.
Each Darlington pair inside the ULN can handle up to 500mA and the maximum voltage can be as high as 50VDC.
Power Supply for Stepper Motor Drive
A stepper motor may run at voltages varying from 5 V to 12 V and similarly, the current draw will be somewhere in the range of 100 mA to 400 mA.
The supplier will give the motor specifications. Accordingly, we must design the supply. The power must be regulated so that fluctuations in speed and torque can be avoided.
Power Supply Unit
Since the 7812 voltage regulator can handle only up to 1A of current, the outboard transistor is used here. It can handle 5 A of current. A proper heat sink must be provided depending on the total current draw.
The above block diagram shows the flow of connections and the interconnections between the driver board’s various components.
Miscellaneous Components
- Switches, Potentiometers
- Heat sink
- Connecting wires
Comprehensive Stepper Motor Drive
The stepper motor drive is a dumb piece of electronics unless you program the microcontroller to give signals correctly to the stepper motor via the driver.
A stepper motor can operate in many modes like full step, wave drive, or half-stepping (Please refer to the article on Stepper Motor for the sequence of steps).
Hence, we must make the driver interactive enough to take command from the user and do the required kind of stepping. Also, we must control the speed of rotation. A start/stop command must start or stop the motor rotation.
To accomplish the above functions, we need to use additional pins on the micro-controller. Two pins are required to select the kind of stepping and to start or stop the motor.
One pin is required to connect a pot, which will act as a speed controller. The ADC inside the micro-controller will be used to control the speed of rotation.
Program Algorithm
- Initialize the port pins in input/output modes.
- Initialize the ADC module.
- Create separate functions for half-stepping, full stepping, and wave drive and delay.
- Check two port pins for operating mode (00-stop, 01-wave drive,10-full step, 11-half stepping).
- Go to the appropriate function.
- Read the Potentiometer value via the ADC and accordingly set a delay value.
- Complete one cycle of sequence.
- Go to step 4.
Driver Board
If you plan to make your own board using CAD software like EAGLE, ensure that you provide sufficient thickness for the motor currents to flow without overheating the board.
Also, as motors are inductive components, care must be taken not to disturb the other signal paths through interferences. Proper ERC and DRC checks must be followed.
Note:
Building a Stepper motor driver is more about selecting the proper power supply and driver, and the selection of the micro-controller is secondary.
Many micro-controllers can do the simple job of rotating the motor. Still, the design considerations regarding the voltages and currents you must focus on while designing the driver.
Also, a single driver board must handle voltages and currents over a wide range and not only for a single motor. This will enable you to use the same board in many different projects rather than making a new one every time.
