Day 24: Controlling a relay with the Raspberry Pi

In order to control the circuit presented on Day 23 with the Raspberry Pi, I used the L293D motor driver.

The relay requires 40 mA and the GPIO can provide up to 16 mA. Using the L293D motor is a little overkill since it can handle up to 600 mA. I believe that the ideal solution would be using a transistor as shown in this article but I don’t have one now.

It is extremely important to use the protection diode in the proper position. I have been told that the 1N4148 is more suitable for this because it has a better response time. By now, I only have a 1N4001. I have read in some blogs people saying they use the 1N4001 without problems, so I gave it a chance.

Relay_Pi

I used the GPIO #17 pin to activate the relay through the L293D. I connected +5V from a external power source to the line in the top of the image  and its ground to the line in the bottom of the image.

As usual, I used my PiEater library to control the GPIO from my desktop computer. Since this is just a quick test, I added a new check box in my previous Truck Driver program:

TruckDriver_Relay

And, voilà!

Green  Red

Day 20: MC-1 Part I: Hardware

The MC-1, abbreviation for Monster Car 1, is based on parts of a car that once was remote controlled. My wife chose this name because she thinks it is ugly as a monster.

The front wheels are turned by a solenoid. Since the current provided by the L293D is limited, I created this workaround. When the servo moves, it causes the paper clips to close an electric circuit and activate the solenoid.

Relay-Workaround

I have created a standard for the wiring–The connectors that provide power are females and the one that receive power are males. Hence, I don’t have energized male connectors touching each other causing short-circuits. I used glued tape to group the wires together and label them. In this way, it will be easier reconnect the chassis to the board.

MC1-Board MC1-Chassis

I used Velcro to attach the breadboard and the Raspberry Pi to the car. This is how the final assembly looks like.

MC1-v1.0

Day 17: Controlling a DC motor

I bought this car in a second-hand-stuff shop. Originally it was remote-controlled but when I bought it, it no longer had the remote control. I don’t know the motor specification. This car has five AA batteries (7.5V), so I think it is safe to use my 5V power source. I put it on a box to avoid it to run away.

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This time I used the L293D attached to GPIO 18 and 23 in a way I can make the motor run forwards or backwards.

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I used the Servo Blaster library as presented on Day 14. In order to run the motor forwards, I kept one signal at zero and changed the other one.


echo "2=0" > /dev/servoblaster

echo "5=500" > /dev/servoblaster

To run backwards, I inverted the signals:


echo "5=0" > /dev/servoblaster

echo "2=500" > /dev/servoblaster

It worked with values from 300 to 2000.

When the motor runs forwards, the white LED is on. The LED is connected after the L293D.

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When the motor runs backwards, the green LED is on. The LED is connected before the L293D.

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Day 12: Playing with LEDs (III) – PWM and L293D

This time I replaced the red LED in the circuit I used on Day 11 for a ultra bright white LED.

The white LED requires more power than the Pi can provide, so I added the external power source used on Day 9 and a motor control chip, the L293D. I did the wiring based on this Adafruit tutorial but my Cobbler is connected in the inverted position.

This is the final circuit:

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Notes:

  • I used the following wire color guidelines: Black for ground, Red for Vcc, Yellow for data, and Blue for control.
  • The white LED can take up to 80mA and is connected to 100/3 = 33 Ohms resistor.
  • The green LED is connected to a 330 Ohms resistor.
  • I used an external 5V power source connected to the bottom-right corner.

The following picture shows the connections from another direction:

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This is the final result: