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

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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:

Day 9: Playing with LEDs (II) – White LEDs

This time, I used ultra bright white LEDs. These LEDs work in a higher voltage (3.0 to 3.8V) and can take a higher current, too.

The first one has 140,000 mcd of luminosity in a 12 degree viewing angle. I used a 100 ohms resistor to limit the current to 20 mA:

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The second one has a 30 degree viewing angle and can take up to 80 mA. I used two 100 ohms resistors in parallel resulting in 50 ohms, implying in 50 mA of current:

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The problem with the second one is that it does not have the “cut” in its side indicating the catode terminal. The catode is shorter but if someday I cut them in the same size, it would be harder to tell which is which.

Day 8: First soldering

I bought a 5.1 V power converter that had a round connector. As I do not have a corresponding female connector, I decided to cut it off and solder some wires in order to be able to connect it to my breadboard.

Soldering

Eventually I read a little more about soldering and realized this was not a good one :(. But at least it works!

Day 7: Playing with LEDs (I) – Red LED

Since I don’t have a hardware background, I have to start from the beginning.

This circuit get power from a 5 Volts power converter and use a 220 ohms resistor:

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Of course, the power switch is optional :).

I used the Led Calculator to calculate the resistor’s value. I assumed this LED has 2 Volts of forward voltage at can take up to 15 mA.