# Microcontroller Wiring First Checks

Learn the first checks before blaming firmware: power, ground, pin mapping, signal direction, and measurement points.

## Outcome
Inspect a simple controller circuit with less guesswork and fewer fried parts.

## Safe first step
Disconnect power before changing wiring, then verify voltage before connecting a device.

## Ladder steps
### 1. Name power rails
Know the voltage each part expects.

Check: The supply voltage matches the component rating.

### 2. Prove common ground
Signals need a shared reference.

Check: Ground points measure continuity where intended.

### 3. Map pins
Board labels, code pin names, and physical pins can differ.

Check: The code and wiring refer to the same pin.

### 4. Measure before load
A no-load voltage check catches obvious mistakes.

Check: Voltage is in range before the component is connected.

## Examples
### Check supply voltage
```sh
Multimeter: DC volts across VCC and GND
```
Expected signal: Voltage near the expected rail

### Verify shared ground
```sh
Continuity check between grounds
```
Expected signal: Continuity only where ground should be common

### Match labels to physical pins
```sh
Read board pinout before wiring
```
Expected signal: The chosen pin supports the needed function

## Common traps
- Moving wires while powered.
- Assuming all board pins tolerate 5V.
- Trusting a breadboard rail without measuring it.

## Practice task
Draw a three-wire sensor connection and mark power, ground, signal, expected voltage, and measurement point.

## Next steps
- Learn pull-up resistors.
- Learn PWM vs digital output.
- Learn motor driver safety.

## Related
- [Command-line foundations for project logs](/learn/linux/command-line-foundations/)