Components

	ECP-U1C104MA5 Panasonic Electronic Components	x 2
	1N5819WS Hottech(合科泰)	x 8
	S9012_C2931721	x 4
	S9013W J3	x 6
	RT0805BRE0710KL YAGEO	x 8
	AECR0805F1K00K9	x 10

Tools, APP Software Used etc.

EasyEDA

Description

W307186ASV62_Gerber_PCB_DUAL-H-Bridge

by makeriot2020

on May 27, 2022

Many of us have old toys laying around the house, they belong to our children or the children of our friends. In this article, I will attempt to show you how to give an old toy car new life, as well as hopefully teach a child a few interesting things with electronics.

The inspiration for this article comes from my friend’s 7-year-old boy, who, way too clever for his age, always has a lot of very interesting questions. His mother and I have thus decided to do an experiment:

“Let us try to teach him Arduino programming, so he can start to make his own toys”

Obviously, the challenges in this venture are many…

To name a few:

The boy speaks only Thai, so English is a no-go.

Soldering is out of the question, due to his age, as well as safety issues – All teaching will have to be done on a breadboard.

My challenges apart, this is a project that many people would want to attempt, so it is important to start with a bit of theory.

Controlling a DC Motor from a microcontroller

DC motors, like those found in toy cars, are inductive loads, and that means that they induce electromagnetic fields when switched on or off. These EMF fields can damage your sensitive microcontroller quite easily. Another thing to remember is that your typical microcontroller can only source or sink in the region of 25mA to 50mA of current, not quite enough to drive a motor, let alone a toy car.

Directional control of the motor

In our toy car, we would definitely want the driving motor to be able to change direction, meaning spin forwards or backwards, thereby changing the direction that the car is travelling. This is achieved by using a circuit called an H-Bridge. In this circuit, four transistors, either BJTs or MOSFETs are arranged in a particular way to allow us to change the direction that the motor spins by changing certain logic signals.

Implementing an H-Bridge with switches

In the picture above, we simulate the H-Bridge circuit using slide switches in order to explain the method of operation. It should be clear that the direction is changed by switching on diagonally opposite switches.

Driving a motor with a transistor

In the picture above, we implement a simple, one-directional motor control circuit using a single transistor. This circuit still has the limitation that the motor can only spin in a single direction.

Half of an H-Bridge

In the circuit above, we combine the two motor driver circuits (with PNP and NPN transistor ) to complete one half of the H-Bridge circuit. This circuit still has the limitation that we can only spin the motor in a single direction.

The completed H-Bridge circuit

In the picture above, we added another half H-Bridge to complete the circuit. We will thus have 2 PNP and 2 NPN transistors, which form the completed circuit. This circuit will give us full bi-directional control of the motor. We can also control the speed of the motor if we apply a suitable PWM signal to the bases of the NPN transistors – we do need to be careful of SHOOT THROUGH and shorts though.

My proposed Motor Driving Circuit

the inside of the toy car, without the old broken circuit-board

In the picture above, we can clearly see that there is not a lot going on inside this toy car. An On-Off switch is connected to the battery compartment, and two wires go to the drive- and steering motor.

Interfacing this car to a microcontroller is thus going to require two separate H-Bridge circuits. One for the drive motor, and the second for the steering.

Dual H-Bridge Circuit diagram

I have designed the circuit above to control both motors of the toy car, the control signals are simplified to 2 per H-Bridge, and a common PWM signal to control speed.

Code

Basic Testing Code

Arduino

int MotorFwd = 4;
int MotorRev = 5;
int MotorLeft = 6;
int MotorRight = 7;
int PWM_Pin = 3;

void setup() {
// Set Initial States for the bridge, to avoid floating pins causing shorts etc.
    digitalWrite(MotorFwd,LOW);
    digitalWrite(MotorRev,LOW);
    digitalWrite(MotorLeft,LOW);
    digitalWrite(MotorRight,LOW);
// Pull PWM pin LOW as well
    digitalWrite(PWM_Pin,LOW);
//  Now we can set the pin directions, this way, all pins will always initialise in a correct state
    
    pinMode(MotorFwd,OUTPUT);
    pinMode(MotorRev,OUTPUT);
    pinMode(MotorLeft,OUTPUT);
    pinMode(MotorRight,OUTPUT);
    pinMode(PWM_Pin,OUTPUT);
    // Let us do a very simple square circuit...
// Start PWM
   analogWrite(PWM_Pin,230); // Medium High speed
   steering_center();
   stop_motion();
   delay(200);
}

void loop() {

   
// Start Driving FWD
   drive_fwd();
   delay(2000); // 2 seconds;
   steer_left();
   delay(500); // experiment with this delay
   steering_center();
   delay(50);
   steering_right();
   delay(250);
   steering_center();
   delay(50);
   
    
}

// Some short Functions
void steering_center() {
    digitalWrite(MotorLeft,LOW);
    digitalWrite(MotorRight,LOW);
}

void steer_left() {
    digitalWrite(MotorLeft,HIGH);
    digitalWrite(MotorRight,LOW);
}

void steering_right() {
    digitalWrite(MotorLeft,LOW);
    digitalWrite(MotorRight,HIGH);
}

void stop_motion() {
    digitalWrite(MotorFwd,LOW);
    digitalWrite(MotorRev,LOW);
}

void drive_fwd() {
    digitalWrite(MotorFwd,HIGH);
    digitalWrite(MotorRev,LOW);
}

void drive_rev() {
    digitalWrite(MotorFwd,LOW);
    digitalWrite(MotorRev,HIGH);
}

Schematic and Layout

Schematic

Schematic_DUAL-H-Bridge_2022-05-30.png

Download BOM(Bill of materials)

May 30,2022

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W307186ASV62_Gerber_PCB_DUAL-H-Bridge

2 Layers PCB 40.6 x 68.6 mm FR-4, 1.6 mm, 1, HASL with lead, Green Solder Mask, White silkscreen

1161

Published: May 30,2022

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