ULN2803

Darlington driver

ULN2803 8-channel Darlington array (18-pin) — drives relays/steppers/solenoids from logic. Like the ULN2003 with an 8th channel.

Manufacturer datasheet

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In stock

Specifications

No specs listed.

Pinout

Pin	Name	Functions	Notes
1	IN1	GPIO	Input 1
2	IN2	GPIO	Input 2
3	IN3	GPIO	Input 3
4	IN4	GPIO	Input 4
5	IN5	GPIO	Input 5
6	IN6	GPIO	Input 6
7	IN7	GPIO	Input 7
8	IN8	GPIO	Input 8
9	GND	GND	Ground
10	COM	POWER	Common (flyback cathodes)
11	OUT8	—	Output 8
12	OUT7	—	Output 7
13	OUT6	—	Output 6
14	OUT5	—	Output 5
15	OUT4	—	Output 4
16	OUT3	—	Output 3
17	OUT2	—	Output 2
18	OUT1	—	Output 1

Interactive pinout

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ULN2803

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Starter code

Community starter examples — minimal, unofficial, and provided to get you wiring fast. Verify against the manufacturer datasheet before relying on them.

Arduino (C++)

arduino

// ULN2803A Darlington sink driver — community starter example
// Each input drives a sinking output (relay/solenoid/LED low side).
#if defined(ESP32)
  #define IN_PIN 26
#else
  #define IN_PIN 8
#endif

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

void loop() {
  digitalWrite(IN_PIN, HIGH);   // OUT pulls its load to GND
  delay(500);
  digitalWrite(IN_PIN, LOW);    // output off (open)
  delay(500);
}

MicroPython

python

# ULN2803A Darlington driver (ESP32) — community starter example
from machine import Pin
import time

drv = Pin(26, Pin.OUT)   # IN1 -> OUT1 sinks the load

while True:
    drv.value(1)   # load ON (sunk to GND)
    time.sleep(0.5)
    drv.value(0)
    time.sleep(0.5)

Wiring

Pin	Arduino Uno R3	ESP32 DevKitC (WROOM-32)	Notes
IN1	D8	GPIO26	Logic input; 3.3 V drives it fine
GND	GND	GND	Chip ground (pin 9)
COM	-	-	Flyback-diode common: tie to the load's + supply for inductive loads
OUT1	-	-	Open-collector sink: load between +V and OUT1

Typical uses

Driving relays, solenoids, and steppers (low side)
Switching up to 8 loads from logic pins