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Wemos Motor Shield

Sep 10, 20246 min read

The ports of the ESP8266 can yield a maximal current of 12 mA. This is perfect to control other ports and drive LED, but way too low to drive even the smallest motors and other real world objects. Moreover, the maximum voltage of 3.3 volt will be insufficient in most situation to drive these objects. In order to handle bigger currents and higher voltages there is the motor shield.

Although the name suggest that this shield must be coupled to motors, it is in fact very suited to drive any electrical object. Typical examples are electromagnets, lamps and buzzers.

This shield can handle 15 volt and 1.2 ampere (3.2 ampere peak) for each of the two motor outputs. For even higher currents and voltages we need more powerful motor shields, a relay.

Motor shields use PWM, see image below, signals to control the power given to the motor, and hence the speed, while preserving maximal torque. The wave form is exactly identical to the PWM signals used to control to position of a servo motor. Here the motor does not contain a feedback mechanism for the position. The duty cycle of the PWM signal just controls the speed. By switching the wires or the direction from the motor shield the motor can turn in the reverse direction. Some motor shields have additional options, like short circuiting the connections of the motor to stop it as fast as possible.

PWM

There are two version of the motor shield used in the lab. Their use is very similar, but there are differences in the hardware as well as in the software. We will discus both versions.

Both versions of the motor shield are however contected to same only require different software.

The shield is connected by stacking it on top of the Wemos D1 Mini, or next to it on a triple base. This will provide a communication channel and a ground. However power is not provided this way. The shield must be powered by an external power source for most applications.

Note

In for the first assignment you can use the 5V output of the Wemos D1 Mini to power the shield. This is only possible if the motors are not too power hungry. For later application you will need to consinder power usage.

The motor shield has 6 IO pins, 4 of which are used to control the motors the two A pins and the two B pins. It also has a VM and GND pin, for voltage and ground respectively. The VM pin is used to power the motors, and the GND pin is used to ground the motors. For our toy motors, we can use the 5V output of the Wemos D1 Mini to power the motors by connecting a jumper cable from the bottom right 5V pin to the VM pin on the motor shield. For the ground we do not need to do the same, because it is already connected through the stacking of the shields.

To connect the motor we connect both leads to A1 and A2 or B1 and B2. The order does not matter, but the motor will turn in the opposite direction if the leads are switched. See the image below for the connections.

Motor connections

Wemos Motor shield version 1.0.0

This motor shield uses WEMOS_Motor_Shield_Arduino_Library and comes with some examples.

A basic example to speed up the motor connected to output A in small steps is:

#include "WEMOS_Motor.h"
 
#define I2C_ADDRESS 0x30
#define PWM_FREQUENCY 1000
 
Motor MA(I2C_ADDRESS, _MOTOR_A, PWM_FREQUENCY); // define Motor A
 
void setup() { }
 
void loop() {
	for (int duty = 40; duty <= 100; duty += 1) {
		MA.setmotor( _CW, duty); // _CW: Clock Wise; _CCW: Counter Clock Wise
		delay(200);
	}
	MA.setmotor(_STANDBY);
	delay(500);
}

Wemos Motor shield version 2.0.0

This moter shield uses LOLIN_I2C_MOTOR_Library and comes with some examples.

Note

This libary has a notable issue when used in combination with the Wemos OLED button shield. They both use the same namespace

A basic example to speed up the motor connected to output A in small steps is:

#include <Wire.h>
#include <LOLIN_I2C_MOTOR.h>
 
#define PWM_FREQUENCY 1000
 
LOLIN_I2C_MOTOR motor(DEFAULT_I2C_MOTOR_ADDRESS); 
	//I2C address 0x30 SEE NOTE BELOW
 
void setup() {
	//wait until motor shield ready.
	while (motor.PRODUCT_ID != PRODUCT_ID_I2C_MOTOR) {
		motor.getInfo();
	}
}
 
void loop() {
	motor.changeFreq(MOTOR_CH_BOTH, PWM_FREQUENCY);
	motor.changeStatus(MOTOR_CH_A, MOTOR_STATUS_CCW);
	for (int duty = 40; duty <= 100; duty += 1) {
		motor.changeDuty(MOTOR_CH_A, duty);
		delay(200);
	}
	motor.changeStatus(MOTOR_CH_A, MOTOR_STATUS_STANDBY);
	delay(500);
}

Troubleshooting

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