Week 9: Input Devices

• Regulate incoming DC voltage
• Protect batteries from overcharging
• Stabilize energy input regardless of fluctuations

After the charge controller, the output passes through a voltage regulator, stepping down the voltage from ~14V to 5V, which is used to power a Seeed XIAO microcontroller through its 5V input pin.

Current Peaks and PCB Design Considerations

Schematic design

• Pin headers (4 pins) for the motor phases and Components for the boost converter, voltage regulator, and solar panel charger.


• A 6-pin header for the INA sensor

• The XIAO module, whose footprint already includes properly spaced pads

• Diodes (×42), mainly defined by their footprint

A key detail in the circuit architecture is the 5V input of the XIAO, where two power sources are connected:
• One from the solar panel charging system
• One emergency input
Both lines are controlled using diodes, allowing automatic power selection without backfeeding between sources. This ensures safe and seamless switching depending on availability.

PCB Layout

• For updating the board, we need to using the button located in the top menu

• Routing is performed following the connection guides automatically generated by KiCad from the schematic

Copper fill (F.Cu layer)

• The copper pour (fill) tool is selected
• The board area is outlined as desired
• Press “B” to refill zones

Board outline (Edge.Cuts layer)

• This step creates the physical outline of the PCB
• A 2 mm line width is used to match the cutting tool diameter

Drilling layer (User.1)

• Holes are drawn manually as filled circles
• Minimum radius must be 0.4 mm, since the tool diameter is 0.8 mm
• In this case, a radius of 0.5 mm is used for safety and tolerance

Drilling Process

Traces Milling

To fix this, the image must be inverted in the “Convert SVG Image” module, so that the tool removes only the surrounding copper and preserves the traces. Just click on the button invert

For this step, a 0.40 mm flat end mill is used with a feed rate of 4 mm/s, and the origin is again set to (0,0,0).

Board Outline

1. Click “Delete All” to remove any previously loaded jobs.
2. Click “Add” and select the .rml files generated earlier in MODS.

• If drilling is done after milling traces, it may damage or lift the copper tracks.
• If the outline is cut first, the board may move, ruining the remaining processes.

Tooling and Setup Considerations

1. Securing the PCB material to the bed.
2. Setting the X, Y, and Z origin points.
3. Loading the .rml files in the correct order.
4. Running each process sequentially (drilling, traces, cutout).
5. Changing tools and recalibrating Z between each step.

Solder

The soldering temperature used is 700°F (~370°C), which provides a good balance between efficient heat transfer and control. If the temperature is too low, the solder may not flow properly, resulting in weak or “cold” joints. On the other hand, excessively high temperatures can damage components, lift PCB pads, or degrade the board material.

Soldering Temperatures

Hardware Definitions

 const int pinCorriente = D0;
 const int pinVoltaje = D1; 

ADC Configuration

 // Parámetros ADC 
const float VREF = 3.3;
 const int ADC_RES = 4095; 

Sensor Calibration

 // AJUSTAR CON CALIBRACIÓN float offset = 1.65; float sensibilidad = 0.1; 

Noise Filtering

 // Promedio const int samples = 10;

float leerPromedio(int pin) {
long sum = 0;
for (int i = 0; i < samples; i++) {
sum += analogRead(pin);
delay(2);
}
return sum / (float)samples;
}

Initialization

 void setup() { Serial.begin(115200); } 

Current Measurement

float rawCorr = leerPromedio(pinCorriente);
 float voltCorr = rawCorr * (VREF / ADC_RES);
 float corriente = (voltCorr - offset) / sensibilidad; 

Voltage Measurement

float rawVolt = leerPromedio(pinVoltaje); 
float voltaje = rawVolt * (VREF / ADC_RES); 

Power Calculation

float potencia = voltaje * corriente; 

Serial Output

Serial.print("Voltaje: "); 
Serial.print(voltaje); 
Serial.print(" V | Corriente: "); 
Serial.print(corriente); 
Serial.print(" A | Potencia: "); 
Serial.print(potencia); 
Serial.println(" W");

delay(500);

 
                                        const int pinCorriente = D0; 
                                        const int pinVoltaje = D1; 
                                        // ===== ADC ===== 
                                        const float VREF = 3.3; 
                                        const int ADC_RES = 4095; 
                                        // ===== Calibration ===== 
                                        float offset = 1.65; 
                                        float sensibilidad = 0.1; 

                                        const int samples = 10; 
                                        float leerPromedio(int pin) { 
                                            long sum = 0; 
                                        for (int i = 0; i < samples; i++) { 
                                                sum += analogRead(pin); delay(2); 
                                            } 
                                            return sum / (float)samples; 
                                        } 
                                        // ===== Setup ===== 
                                        void setup() { 
                                            Serial.begin(115200); 
                                        } 
                                        // ===== Loop ===== 
                                        void loop() { 

                                            float rawCorr = leerPromedio(pinCorriente); 
                                            float voltCorr = rawCorr * (VREF / ADC_RES); 
                                            float corriente = (voltCorr - offset) / sensibilidad; 
                                            
                                            float rawVolt = leerPromedio(pinVoltaje); 
                                            float voltaje = rawVolt * (VREF / ADC_RES); 
                                            
                                            float potencia = voltaje * corriente; 

                                            // ===== OUTPUT ===== 
                                            Serial.print("Voltaje: "); 
                                            Serial.print(voltaje); Serial.print(" V | Corriente: "); 
                                            Serial.print(corriente); Serial.print(" A | Potencia: "); 
                                            Serial.print(potencia); Serial.println(" W"); 
                                            delay(500); 
                                        }