I am building a robot using one of my Raspberry Pi 2s. I bought a chasis that came with wheels and 4 motors. Figuring out how to control the motors seemed unnecessasrily difficult to figure out. I am not terribly familiar with electronic circuits and chips.
I quickly learned that I need to master using the L239D chip to succeed. This is because a microcontroller cannot provide enough power to a motor for such an application directly. You need to use a separate battery back, and use the microcontroller to determine if and how the motor gets power from the batter. The L239D is a very popular chip for doing just that.
It took me too much trial and error to figure out how to use the L239D chip. So, I wrote this guide as the guide that I wish I had when I was learning how to set up my robot.
To write this guide, I assembled the following components I had handy.
- Breadboard - For learning the wiring, a standard divided breadboard is easiest.
- Microcontroller - I used my Arduino clone from Sparkfun. It is the simplest to set up. Any microntroller like a Pi or BeagleBone will do just fine, though.
- Battery Pack - A 9 volt battery is fine. I happened to have a 4xAA battery holder handy, so I used that.
- Jumper Cables - I strongly prefer to use red for positive, black for negative, and other colors for digital connections.
- L293D Chip - I ordered 10 of them from Amazon for about $9.
- Motor - I had a small motor from my Sparkfun inventors kit handy. The motors for my robot are much more powerful, but this one was fine for the guide.
There are many useful diagrams of the chip on the web, such as this:
However, I had to piece together information from many sources before I could get a very clear idea of how the chip is intended to be used.
Note the direction on which the pins are numbered. The functionality and relationship of each pin is not always very clear. Refer to the number photo below.
Pin 1 and Pin 9 are not used in these instructions. The purpose of these pins is to take input from a microcontroller's PWN pin to allow variable amounts of power from the battery to flow to the motor. The digital pins 2,7,15, and 10 determine if power flows from the battery to the motor, but pin 1 and pin 9 can be used to determine if some percentage of the power will flow. If you do not use these pins, the battery power is delivered at full power to the motor. Pin 1 affects the motor connected to the left side of the chip, and Pin 9 affects the right side.
These pins work together in pairs to control if power flows from the battery to the motor. For example, The digital pin from the microcontroller connects to Pin 2, so Pin 2 is called the input pin. Pin 3 connects to either the positive or negative lead of the motor, so is called the output pin. In general, if you send an "on" signal to Pin 2, it will cause power to flow through through Pin 3 to the battery. The exception to this is cases where the negative lead from the motor is also sent to "on." This interaction will be described more below. Pins 7 and 6, Pins 10 and 11, and Pins 15 and 14 have this same relationship.
The chip itself requires power to run. This power is supplied to pin 16, typically from a a 5v output pin on your microcontroller.
The positive lead from the battery is connected to pin 8.
The negative lead (ground) of the battery can be connected to any of the grounding pins, Pins 4, 5, 12, or 13.
For reference:
Pin 1: PWM pin for the left hand side of the chip.
Pin 2: Input pin controlling output for pin 3.
Pin 3: Output pin controlled by pin 2.
Pin 4: Ground
Pin 5: Ground
Pin 6: Output pin for pin 7.
Pin 7: Input pin for pin 8.
Pin 8: Power input from the battery
Pin 9: PWN pin for the right hand side of the chip.
Pin 10: Input pin for controlling pin 11.
Pin 11: Output pin controlled by pin 12.
Pin 12: Ground
Pin 13: Ground
Pin 14: Output pin controlled by pin 15.
Pin 15: Input ping controlling pin 14.
Pin 16: Power input for the chip itself.
So, conceptual, in order to use the chip, you supply power to the chip itself through pin 16. Then you supply power from the battery through pin 8.
Then, in order to control the direction of a motor, you use the 2 pairs of input and output pins on one side of the chip. Then you you can control the direction of the motor by connecting the positive lead of the motor to one output pin, and the negative lead to the other.
For example, if you use the left side of the chip, you might use pins 2 and 3 for positive, and pins 6 and 7 for the negative. Then, depending on how you set the inputs, you get the following effects:
Pin 2 off and pin 7 off: The motor is off Pin 2 on and pin 7 off: The motor goes forward (the battery power flows through the positive lead). Pin 2 off and Pin 7 on: The motor moves backward (the battery flows through the negative lead). Pin 2 on and Pin 7 on: The motor is off (power can only flow in one direction).
You can additionally set how fast the motor goes by sending a signal to the PWM input on pin 1.
The chip itself needs power to run. This is separate from the power that will go the motor, and separate from the digital output to command whether to give juice to the motor. Your microcontrol almost certainly has a 5v out that is perfect for this. On the Arduino, it is conveniently labeled "5V."
I prefer to use red jumpers for positive power, and black for negative/ground. After this step, your L29D will have the power it needs to run its logic.
Use a red jumper to connect the 5v of your microcontroller to the power strip of the breadboard.
Next, ground the breadboard. This ground will be used by everything plugged into the L293D. Use a black jumper to connect the ground on the breadboard to the ground on your microcontroller.
Now that the breadboard is set up, you can complete the circuit to the L293D.
- Use a red jumper cable to connect pin 16 to the positive power channel in the breadboard.
- Use a black jumper to connect pin 13 to the negative channel in the breadboard.
Next we will provide power for motor. The battery pack will provide the power to the motor (when commanded by the microcontroller). After this step, the batter will be wired up, but the motor still won't be connected, nor will the commands from the microcontroller.
Plug the red lead from the battery pack in the breadboards other positive channel. Then use a red jumper cable to connect from the positive channel to pin 8 on the L239D. This provides the power from the battery that will be used to control the motor.
Then connect the black lead from the battery into the ground channel from the other side. This will just use the existing ground on the microcontroller.
In this step, you will connect the digital pins from the microcontroller to the chip.
In this application, the motor is controller by digital pins that can be either on or off (usually called GPIO) pins. By connecting digital pins to the L239D, you can tell the L239D to allow electricity to flow through the motors red positive lead, or black negative lead. If the batter power flows through the red lead, the motor will go forward, if through the black lead, it will go backward. If electricity goes through either or both, the motor will not move. In this way, you need two inputs to fully control the direction of the motor.
I chose pins 7 and 4 on the Arduino due to their convenient placement. Use a jumper that is not black or red for each digital pin that you choose.
Then connect them to the L239D inputs, but connecting them to pins 2 and 7. These are the 2 "input" pins on this side of L239D.
The L239D is now ready to receive commands.
In this final step, you will create the circuit for the motor.
This is the last step in creating the cirtuits. You simply need to pair the red and black leads from the motor with the digital pin inputs, by connecting them to pins 3 and 6 on the L239D. This pairs them with the inputs on pin 2 and 7.
Now you can control the direction of the motor with the microcontroller. Here is an Arduino sketch that causes the motor to spin in one direction for 1 second. Then rests for a second, then spins the other way, and then rests, and so forth.
void setup() {
// put your setup code here, to run once:
pinMode(4, OUTPUT);
pinMode(7, OUTPUT);
}
void loop() {
// put your main code here, to run repeatedly:
digitalWrite(4, HIGH);
digitalWrite(7, LOW);
delay(1000);
digitalWrite(4, LOW);
digitalWrite(7, LOW);
delay(1000);
digitalWrite(4, LOW);
digitalWrite(7, HIGH);
delay(1000);
}
Note that you only used one side of the L239D. There are 2 more inputs and outputs (pins 15/14 and pins 10/11). That means that you can use the same L239D to control another motor. In my application, I use 2 L239Ds to control 4 wheels of my robot independently.
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