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Built-in project · Arduino Uno R3

ULN2003A solenoid from an Arduino on an Arduino Uno

Blink on pin 13 switches a 12 V, 40 ohm solenoid through a ULN2003A: 0.27 A that a pin could never give, with the COM diode catching the coil when it lets go. The whole build, an Arduino Uno and 3 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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The parts retail for about $33. On Mokxi they're free.

ULN2003A solenoid from an Arduino · Arduino Uno R3live0.000 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 · Arduino Uno R3
// Blink: the smallest thing a board can do.
//
// Pin 13 has the LED soldered next to the USB socket, so LED_BUILTIN is 13.
// Wire an LED and a 220 ohm resistor from pin 13 to GND to see it on the
// breadboard too.
//
// delay() puts the chip to sleep between timer ticks rather than spinning, so
// this sketch costs the simulator almost nothing while it waits.

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);
  delay(500);
}

Parts list

5 parts, plus the jumper wires and a bench instrument. The parts retail for about $33; on Mokxi they're free, and so are the instruments.

How it is wired

4 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.

  • Arduino Uno R3 pin 13; ULN2003A Darlington array pin 1B; Oscilloscope pin CH2
  • Ground: Arduino Uno R3 pin GND; ULN2003A Darlington array pin E; Oscilloscope pin GND
  • 12 V: ULN2003A Darlington array pin COM; Solenoid pin 1
  • ULN2003A Darlington array pin 1C; Solenoid pin 2; Oscilloscope pin CH1

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