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Built-in project · SparkFun Pro Micro

Pro Micro blink

A board with no LED on pin 13 blinks its RX lamp instead, with an LED on pin 9 beside it wired the ordinary way around. The whole build, a SparkFun Pro Micro and 2 more parts, runs here in your browser on the firmware below; open it in the editor to change the wiring or the code and run it again.

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Pro Micro blink · SparkFun Pro Microlive0.000 s 0.00x
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The circuit itself, running here on the simulator. Press what can be pressed; click anything else to open it in the editor.

The code

The firmware exactly as the editor opens it. Change a line there and press Run: it compiles in the browser.

sketch.ino · SparkFun Pro Micro
// RX blink: the lamp a board with no pin 13 still has.
//
// Every ATmega32U4 board has an RX and a TX LED, and both are wired from 5 V
// through a resistor to a pin: RX to PB0, TX to PD5. So the pin has to go LOW
// to light one. RXLED1 does that and RXLED0 lets it go dark again.
//
// On a Leonardo or a Micro this blinks the RX lamp beside L. On a SparkFun Pro
// Micro, which does not bring pin 13 out at all, it is the only way to see a
// blink without wiring anything: LED_BUILTIN is still 13 there, and blinking
// it lights nothing.
//
// Pin 9 blinks at the same time the ordinary way round, HIGH for on, so an
// LED and a resistor from pin 9 to GND show the difference side by side.

const int WIRED = 9;

void setup() {
  TX_RX_LED_INIT;
  TXLED0;
  pinMode(WIRED, OUTPUT);
}

void loop() {
  RXLED1;                     // lamp on: PB0 low
  digitalWrite(WIRED, HIGH);  // wired LED on: pin 9 high
  delay(500);
  RXLED0;                     // lamp off: PB0 high
  digitalWrite(WIRED, LOW);
  delay(500);
}

Parts list

4 parts, plus the jumper wires. Every one is in the editor's parts bin.

How it is wired

3 connections, pin by pin, read from the circuit itself. Each line is one set of pins joined together, by a jumper wire or a breadboard strip.

  • Ground: SparkFun Pro Micro pin GND; LED, red pin C
  • SparkFun Pro Micro pin 9; Resistor, 220 Ω pin 2
  • Resistor, 220 Ω pin 1; LED, red pin A

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