Overview

The PCF8591 is a single-chip 8-bit CMOS data acquisition IC manufactured by NXP Semiconductors. It integrates four single-ended (or two differential) 8-bit analog inputs, one 8-bit Digital-to-Analog converter (DAC) output, an internal track-and-hold circuit, and a standard I2CI^2C bus interface.

Standard blue PCB breakout modules bundle the PCF8591 alongside three onboard analog components: an NTC thermistor, a photoresistor (LDR), and a trimmer potentiometer connected to AIN0–AIN2 via removable jumpers. It is widely used in beginner Raspberry Pi and Arduino projects to learn analog-to-digital and digital-to-analog conversion over I2CI^2C.

Quick reference

Operating voltage (VCC)2.5 V to 6.0 V DC
ADC resolution8-bit (256 discrete levels)
ADC channels4 single-ended, 2 differential, or mixed
DAC resolution8-bit (1 analog voltage output pin AOUT)
InterfaceI2CI^2C (Standard 100 kHz)
Default I2CI^2C address0x48 (3 hardware address pins A0,A1,A2→GNDA_0, A_1, A_2 \to \text{GND})
Operating current250 μA250\ \mu\text{A} active / 10 μA10\ \mu\text{A} standby

Pinout

Common 4-pin I2CI^2C + 4-pin Analog breakout header:

PinNameTypeDescription
1VCCPowerSupply voltage (+2.5 V to +6.0 V DC)
2GNDPowerGround (0 V)
3SDADigital Input / OutputI2CI^2C Serial Data
4SCLDigital InputI2CI^2C Serial Clock
5AIN0Analog InputAnalog Channel 0 (connected to LDR on module jumper P5)
6AIN1Analog InputAnalog Channel 1 (connected to Thermistor on jumper P4)
7AIN2Analog InputAnalog Channel 2 (connected to Potentiometer on jumper P6)
8AIN3Analog InputAnalog Channel 3 (free external analog input)
9AOUTAnalog Output8-bit DAC output voltage pin

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageVCCV_{CC}2.53.3 / 5.06.0VDC
Reference VoltageVAGND…VREFV_{AGND} \dots V_{REF}VSSV_{SS}—VDDV_{DD}VAnalog reference range
ADC Conversion Timetconvt_{conv}—90—µsLimited by I2CI^2C clock speed
ADC Non-LinearityELE_L-1±0.5\pm 0.5+1LSB8-bit resolution
DAC Slew RateSRdacSR_{dac}—100—V/msFull-scale step output
DAC Load ResistanceRLR_L10——kΩConnected to AOUT

Control Byte & Protocol

The PCF8591 uses a single control byte sent immediately following the I2CI^2C device address (0x48):

  • Bit 7: Always 0.
  • Bit 6: ANALOG OUTPUT ENABLE (1 = DAC AOUT output enabled, 0 = High impedance).
  • Bits 5–4: Analog Input Programming Mode (00 = 4 single-ended inputs).
  • Bit 3: Always 0.
  • Bit 2: Auto-increment flag (1 = automatically cycle through AIN0–AIN3 on sequential reads).
  • Bits 1–0: Channel Select (00 = AIN0, 01 = AIN1, 10 = AIN2, 11 = AIN3).

VAIN=Byte Value255×VCCV_{AIN} = \frac{\text{Byte Value}}{255} \times V_{CC}

VAOUT=DAC Write Byte255×VCCV_{AOUT} = \frac{\text{DAC Write Byte}}{255} \times V_{CC}

Wiring

PCF8591 Pin→Arduino / Raspberry PiNotes
VCC5V / 3.3VMatch logic level of host MCU
GNDGNDSystem ground
SDAA4 / GPIO 2 (SDA)I2CI^2C Data
SCLA5 / GPIO 3 (SCL)I2CI^2C Clock

Example

cpp
#include <Wire.h>

#define PCF8591_ADDRESS 0x48

void setup() {
  Serial.begin(9600);
  Wire.begin();
}

void loop() {
  // Enable DAC output and read AIN0 (Channel 0)
  Wire.beginTransmission(PCF8591_ADDRESS);
  Wire.write(0x40); // 0x40 = Enable DAC (bit 6), read AIN0
  Wire.write(128);  // Set DAC AOUT to mid-rail (~2.5V)
  Wire.endTransmission();

  Wire.requestFrom(PCF8591_ADDRESS, 2);
  Wire.read(); // First byte returned is previous conversion result; discard
  uint8_t adcValue = Wire.read();

  float voltage = (adcValue / 255.0) * 5.0;
  Serial.print("AIN0 ADC: "); Serial.print(adcValue);
  Serial.print(" | Voltage: "); Serial.print(voltage); Serial.println(" V");

  delay(500);
}

Common mistakes

  • Discarding first I2CI^2C read byte: The PCF8591 uses a pipelined conversion architecture. When reading a channel over I2CI^2C, the first byte returned is the previous channel sample. Always discard the first byte or issue two sequential reads.
  • Forgetting jumper removal for external signals: On standard blue modules, jumpers P4, P5, and P6 hardwire AIN0–AIN2 to the onboard sensors. To read external analog voltages on AIN0–AIN2, remove the corresponding shunt jumper.

Notes

  • PCF8591 vs ADS1115: PCF8591 is 8-bit (256 steps) with DAC output; ADS1115 is 16-bit (65,536 steps) precision ADC without DAC.

Assets & downloads