How to Design Reset Circuit for Microcontroller in PCB Design

To design a reset circuit for a microcontroller in PCB design, use a push-button switch connected to the reset pin with a pull-up resistor to the supply voltage and a capacitor to ground for power-on reset delay. This setup ensures the microcontroller starts correctly and can be manually reset when needed.

Syntax

A basic reset circuit includes these parts connected to the microcontroller's reset pin:

• Push-button switch: Connects reset pin to ground when pressed.
• Pull-up resistor (10kΩ): Connects reset pin to Vcc to keep it high normally.
• Capacitor (0.1µF): Connected between reset pin and ground to create a delay on power-up.

This combination ensures the reset pin is normally high, goes low when the button is pressed, and has a brief low pulse at power-up.

plaintext

Reset Pin --- Pull-up Resistor (10kΩ) --- Vcc
          |
          +--- Push-button --- GND
          |
          +--- Capacitor (0.1µF) --- GND

Example

This example shows a simple reset circuit schematic for a microcontroller:

• Connect a 10kΩ resistor from the reset pin to +5V.
• Connect a push-button from the reset pin to ground.
• Connect a 0.1µF capacitor from the reset pin to ground.

When power is applied, the capacitor briefly pulls the reset pin low, resetting the microcontroller. Pressing the button also pulls the reset pin low to reset manually.

plaintext

Component connections:
- Reset pin to one end of 10kΩ resistor
- Other end of resistor to +5V
- Reset pin to one terminal of push-button
- Other terminal of push-button to GND
- Reset pin to one terminal of 0.1µF capacitor
- Other terminal of capacitor to GND

Output

Microcontroller resets on power-up and when button is pressed

Common Pitfalls

Common mistakes when designing reset circuits include:

• Using no pull-up resistor, causing the reset pin to float and random resets.
• Choosing too large or too small capacitor values, which can cause too long or too short reset pulses.
• Not debouncing the reset button, which can cause multiple resets.
• Connecting the reset pin directly to ground without resistor, which can damage the microcontroller.

Always use a pull-up resistor and a small capacitor for stable reset behavior.

plaintext

Wrong:
Reset Pin --- Push-button --- GND (no resistor)

Right:
Reset Pin --- Pull-up Resistor --- Vcc
          |
          +--- Push-button --- GND

Quick Reference

Component	Value	Purpose
Pull-up resistor	10kΩ	Keeps reset pin high normally
Push-button switch	N/A	Manually pulls reset pin low
Capacitor	0.1µF	Creates power-on reset delay
Reset pin	N/A	Microcontroller reset input

Key Takeaways

Always use a pull-up resistor on the reset pin to avoid floating signals.

Add a small capacitor to ground on the reset pin for a reliable power-on reset.

Use a push-button switch to manually reset the microcontroller safely.

Avoid connecting the reset pin directly to ground without a resistor.

Choose component values carefully to ensure proper reset timing.