As equipment like motors and relays require high current, microcontrollers cannot drive them. In order to drive them, we need special current drivers. Motor relay board comes into the picture because of these requirements. Motor relay board drives motors and relays by supplying sufficient current. It can drive one relay and four DC motors or one stepper motor at a time. The motor relay board eases the task of interfacing external motor and AC devices with the ATmega32 microcontroller. It has ULN2003 drivers for high current applications like motor driving and relay driving circuits for AC device interfacing.

There are three main sections for a motor relay board.

Relay Driver

Using the provided relay circuit, 230V devices can be controlled. This section is helpful for automating the ON and OFF.

Motor Driver

The DC motor can be controlled using this section, there is 4 ULN2003 driver controlled lines for driving motors and each provides sufficient current to control the DC motor.

External Interfaces

* Terminal block (3pin) –for connecting relay IN and OUT
* Terminal block(7pin) – for connecting 4 lines of motor, 1 for power and 2 pins for ground

Connecting the Board

* Power up the board using SW1, power LED will glow.
* Connect the port connector to the default port.
* Shunt the jumpers in J4.
* Use jumper caps to select port pins. First four pins (0, 1, 2&3) are relay selectors. The relay can be connected to 4 pins.
* Use port pins 4,5,6&7 for motors in the order of motor D, C, B&A.
* Set the input port pin correspondingly to turn ON/OFF the relay/motor.


There is an alternate header J3 for accessing individual pins.


The Jumper description is as below for J4.


The relay and motor inputs can be directly accessed by the header J5.


Terminal Blocks

Terminal blocks are used for connecting motor, external supply, and relay controlled equipment. There are three terminal blocks. One is for the motor which is a 7-pin device, another one a 2-pin device for connecting external 12V supply and 3-pin terminal block is used for connecting relay inputs and outputs.

Pin arrangements in terminal blocks are as below.

Relay Block


NC – Normally closed
COM – Common
NO – Normally open

Motor Block


VCC – Supply from external 12V or internal 9V whichever is higher

External Supply Block


12V – External power for motor
GND – Ground

Power Headers

There are two power headers available in this board, J9 for 9V and J7 for 5V.



Motor Operation

There are 4 lines for motor control and both DC motor and stepper motor can be interfaced to the board. The motor can be interfaced to terminal block J8. The pins 2, 3, 4 and 5 are for motor lines.

Stepper Motor

For a unipolar stepper motor, connect 4 lines to the motor terminals and a common terminal to the VCC. Put the jumper cap over 5, 6, 7 and 8 pins of J4 to connect pins to the microcontroller port.
For a bipolar stepper motor, connect 4 lines to each of the terminals. Put the jumper cap over 5, 6, 7 and 8 pins of J4.

DC Motor

For DC motor, connect the motor line to any one of the motor terminals and VCC to the common. Connect the jumper cap on the J4 for the corresponding pin.

Relay Operation

The relay can be operated by shorting any of the first four-port pin pairs of connector J4 with the help of a jumper.

Relay has 3 terminals to connect,

* NO – Normally open
* COM – Common terminal
* NC – Normally closed

Connect the input in COM terminal. NO terminal will be connected to the COM terminal during the relay OFF condition and NC will be connected to the COM terminal during ON condition. The relay can be used to control power devices working up to 230V /7 A.

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