Output devices

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Add an output device to a microcontroller board you've designed and program it to do something.

• Documented what you learned from interfacing output device(s) to microcontroller and controlling the device(s).
• Documented your design and fabrication process or linked to the board you made in a previous assignment.
• Explained the programming process/es you used.
• Explained any problems you encountered and how you fixed them.
• Included original design files and source code.
• Included a ‘hero shot’ of your board.

Group assignment:

• Measure the power consumption of an output device.

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Group Assignment

Measuring power consumption of peristaltic pump:

_{End of group assignment}

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Design and fabrication of the PCB

You can see the documentation for this on my previous weeks' pages: Electronics design & Electronics production

Writing the program

It makes sense to program the microcontroller before connecting other devices, since they might interfere with the upload connection for the code.
The program shown below defines the pin connected to the MOSFET's Gate as an output pin. Every 3 seconds, power is supplied to the pin, which bridges the connection between the Drain and the Source of the MOSFET, connecting the GND of the pump to the common GND and therefore enabling it to run:

// Define the MOSFET pin
const int MOSFET_PIN = 9;

void setup() {
  // Set the MOSFET pin as an output
  pinMode(MOSFET_PIN, OUTPUT);
}

void loop() {
  // Turn the MOSFET on
  digitalWrite(MOSFET_PIN, HIGH);

  // Wait for a short period of time
  delay(3000);

  // Turn the MOSFET off
  digitalWrite(MOSFET_PIN, LOW);

  // Wait for a short period of time
  delay(3000);
}

Now upload the program to the board as described in the embedded programming assignment.

Connection of the output device

I am using the waterpump as my output device this week. A peristaltic pump is a special kind of pump that moves liquids using a flexible tube or hose. It works in a similar way to how our muscles push food through our digestive system.
When the pump starts, one roller presses on the tube, squeezing it. This squeezing creates a seal and prevents the liquid from going backward. Then, as the roller moves along the tube, it pushes the squeezed portion of the tube forward, making the liquid move in the same direction. This process repeats as the rollers keep moving, creating a continuous flow of liquid through the pump.
It is a 12V pump and needs an external powersupply as well as a MOSFET to control it.
MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistor) are commonly used as a switch or an amplifier. They have three terminals: the source, the gate, and the drain, and their conductive behavior is controlled by the voltage applied to the gate.

Components mentioned:

• 5V regulator LM7805 (Input Voltage: Minimum 7V, Maximum 25V Output Current: 1.5A)
• 12V power adapter
• 12V peristaltic pump

Working pump (pumps water every 3 seconds for 3 seconds):

Troubleshooting

In reality it did not work on the first try. The KiCad footprint I used for the MOSFET was outdated and had the pads for Drain and Source switched. This caused the pump to not receive the right voltage and therefore not work. My instructor Ahmed helped me desolder the MOSFET with a hot air gun.

After doing so and soldering the MOSFET back onto the PCB, everything worked perfectly fine!