Embedded Files
EAGLE Schematic
EAGLE Schematic
This is a schematic for the laptop cooling pad circuit that I modeled on Autodesk EAGLE. There are a few inaccuracies to the modeling which I will point out before describing the rest of the schematic. The first are the two rightmost pins on the LCD. On the schematic, these pins are titled "NC" which means not connected, but I used them in the actual circuit. These two pins correspond to the LED+ pin (connected to the 220 ohm resistor) and the LED- pin (connected to ground). The second inaccuracy in the circuit schematic has to do with the fans. There was no symbol for a dc motor in Autodesk EAGLE, so I used ammeter symbols in place of them. This schematic was made purely to visualize the circuit in a more neat way, because the actual circuit was breadboarded.
Eagle Schematic (Continued)
Now that the inaccuracies have been covered, I will describe the rest of the schematic. The main components of the circuit that make up the laptop cooling pad are the microcontroller (Elegoo Mega 2560), temperature sensors (2x TMP36), power transistors (2x IRF520), fans (2x Corsair ML120), and a 16x2 LCD to display the information.
I. Microcontroller
The microcontroller used for this project was an Elegoo Mega 2560. I chose this microcontroller because it has plenty of pins that were necessary for the project. It is positioned towards the back of the cooling pad, and has an i/o shield for its two ports. The biggest of the two ports is what connects to a laptop for data transmission. I used this port to upload my code and collect data from the microcontroller. The other port connects to a 12V AC/DC wall adapter. The 12 volts are required to power the fans. When using the laptop cooling pad, it only requires the wall adapter to be plugged in, as the code is already uploaded to the board.
II. Temperature Sensors
The sensors used for this project were two TMP36 analog temperature sensors. I chose the TMP36 because they are easy to work with and accurate enough for the application in which I am using them. They output a voltage that is linearly proportional to the temperature measured by the sensor. When programming, the analog output of the TMP36 can be quickly converted into a temperature reading, this is covered more in-depth in the code section. The TMP36 has three connections: one for power, ground, and the middle pin is connected to an analog pin on the microcontroller for data transmission. The analog pins used were A8 for the left fan and A9 for the right fan.
III. Transistors
Two transistors were required for this project to meet the power demands of the fans. Because the digital pins on the microcontroller can output only 5V (the fans need 12V), an external power source (the 12V AC/DC adapter) would be needed. To control the power output to the fans, I used two IRF520 power transistors. The sources of the transistors were tied to ground, the drains to the negatives of the fans, and the gates to one of the PWM-capable pins on the microcontroller (I used pins D6 and D7). Whenever the microcontroller outputs a voltage to the transistor, it allows for current to flow between the drain and the source (which powers the fans). This current is proportional to the voltage provided by the microcontroller. By using pulse width modulation (PWM), we can change the voltage output by the microcontroller and control the speed of the fans.
IV. Fans
The fans I used were two Corsair ML120 computer case fans. I was able to fit two of these fans inside of the cooling pad, covering the majority of the area on the top. The positives of the fans were connected to the 12V output of the AC/DC adapter (located on the Vin pin on the microcontroller). The negatives of the fans were connected to the drains of the IRF520 transistors.
V. LCD
In order to show the data recorded by the microcontroller I used a 16x2 liquid crystal display. I connected the rs pin to D12, en to D11 and then LCD digital pins 4-7 to D2-5 on the microcontroller. As mentioned earlier, the two rightmost pins on the schematic which are declared not connected are actually the LED+ and LED- pins, which are connected to +5V and GND, respectively. A 10 kiloohm potentiometer was used to control the brightness of the LCD, and a 220 ohm resistor was connected between +5V and the LED+ pins to limit the current into the LED backlight of the LCD.
Pictures of Components
Elegoo Mega 2560
TMP36 Analog Temperature Sensor
IRF520 MOSFET
Source: https://components101.com/mosfets/irf520-pinout-datasheet-features
Corsair ML120 Case Fan
Source: https://www.amazon.ca/Corsair-ML120-Magnetic-Levitation-CO-9050049-WW/dp/B08DL4RF71
16x2 Liquid Crystal Display
Source: https://www.addicore.com/1602-16x2-Character-LCD-with-I2C-backpack-p/ad156.htm
12V AC/DC Converter
Source: https://www.makerfabs.com/12v-2a-ac-dc-power-adapter-with-cable.html
10K Ohm Potentiometer
Source: https://www.reichelt.com/de/en/potentiometer-horizontal-6-mm-10-kohm-acp-6-l-10k-p110218.html
220 Ohm Resistor
Breadboarded Circuit
Breadboarded Circuit
This is a picture of what the inside of the laptop cooling pad looks like with everything connected. All of the components are shown in this picture besides for the temperature sensors and the fans which are connected but out of the frame.
As seen in the picture, I tried to make everything as compact as possible. Instead of connecting the LCD directly to the microcontroller, I had to keep the wires as flat as I could out of fear that they would interfere with the fans. As a result, the LCD wires had to travel a long way to get to the microcontroller. I also had to reposition the potentiometer, because when I had initially put the fans on, they would touch the potentiometer and not allow the cooler to close.
The MOSFETs can be seen in the breadboard on the right. They had to be placed in the space between the fans because they also were making contact with them.
The LCD and microcontroller fit perfectly into the spaces cut out for them in the 3D design, and they are both fastened to the case with glue. The breadboards have a peel-off adhesive on the bottom that keeps them stuck to the case.
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