Claude-Analog Input on Raspberry Pi Pico

Multi-Channel Analog Input Guide: ESP32 vs Raspberry Pi

Overview

This guide covers implementing 4+ channel analog input systems using ESP32 and Raspberry Pi platforms, with detailed comparisons and implementation strategies.

Hardware Platforms Comparison

Raspberry Pi Pico (RP2040)

  • ADC Channels: 3 only (GPIO 26, 27, 28)
  • Resolution: 12-bit (4096 levels)
  • Voltage Range: 0-3.3V
  • Sampling Rate: 500 ksps
  • Limitation: Requires external ADC for 4+ channels

ESP32-S3

  • ADC Channels: 20 channels (18 usable)
  • Resolution: 12-bit (4096 levels)
  • Voltage Range: 0-3.3V (up to 3.9V with attenuation)
  • Sampling Rate: Up to 83.3 ksps
  • Advantage: Built-in WiFi/Bluetooth, no external ADC needed

Implementation Options for 4+ Channels

Available pins for analog input:

  • GPIO2 (ADC1_CH1)
  • GPIO3 (ADC1_CH2)
  • GPIO17 (ADC2_CH6)
  • GPIO18 (ADC2_CH7)

Arduino Code Implementation:

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void setup() {
  Serial.begin(115200);
  analogReadResolution(12);        // 12-bit resolution
  analogSetAttenuation(ADC_11db);  // 0-3.3V range
}

void loop() {
  // Read 4 analog channels
  int sensor1 = analogRead(2);   // GPIO2
  int sensor2 = analogRead(3);   // GPIO3  
  int sensor3 = analogRead(17);  // GPIO17
  int sensor4 = analogRead(18);  // GPIO18
  
  // Convert to voltage
  float voltage1 = sensor1 * 3.3 / 4095.0;
  float voltage2 = sensor2 * 3.3 / 4095.0;
  float voltage3 = sensor3 * 3.3 / 4095.0;
  float voltage4 = sensor4 * 3.3 / 4095.0;
  
  // Output results
  Serial.printf("Ch1: %.2fV, Ch2: %.2fV, Ch3: %.2fV, Ch4: %.2fV\n", 
                voltage1, voltage2, voltage3, voltage4);
  
  delay(100);
}

Option 2: External ADC Solutions (For Raspberry Pi or Higher Precision)

ADS1115 (4-channel, 16-bit, I2C)

Connections:

  • VDD → 3.3V
  • GND → GND
  • SCL → GPIO10 (ESP32) / GP1 (Pico)
  • SDA → GPIO11 (ESP32) / GP0 (Pico)

Code Example (ESP32):

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#include <Wire.h>
#include <Adafruit_ADS1X15.h>

Adafruit_ADS1115 ads;

void setup() {
  Serial.begin(115200);
  Wire.begin(11, 10); // SDA=11, SCL=10 for ESP32
  
  if (!ads.begin()) {
    Serial.println("Failed to initialize ADS1115!");
    while (1);
  }
  ads.setGain(GAIN_ONE); // ±4.096V range
}

void loop() {
  // Read all 4 channels
  for (int i = 0; i < 4; i++) {
    int16_t raw = ads.readADC_SingleEnded(i);
    float voltage = ads.computeVolts(raw);
    Serial.printf("Ch%d: %.3fV ", i, voltage);
  }
  Serial.println();
  delay(100);
}

MCP3008 (8-channel, 10-bit, SPI)

Connections:

  • VDD → 3.3V
  • VREF → 3.3V
  • AGND → GND
  • CLK → GPIO2 (SPI Clock)
  • DOUT → GPIO4 (MISO)
  • DIN → GPIO3 (MOSI)
  • CS → GPIO5 (Chip Select)

Option 3: Analog Multiplexer (CD74HC4051)

For using 1 ADC pin with 8 input channels:

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// Multiplexer control pins
#define S0_PIN 16
#define S1_PIN 17
#define S2_PIN 18
#define ADC_PIN 26

void selectChannel(int channel) {
  digitalWrite(S0_PIN, channel & 1);
  digitalWrite(S1_PIN, (channel >> 1) & 1);
  digitalWrite(S2_PIN, (channel >> 2) & 1);
  delayMicroseconds(10);
}

void setup() {
  Serial.begin(115200);
  pinMode(S0_PIN, OUTPUT);
  pinMode(S1_PIN, OUTPUT);
  pinMode(S2_PIN, OUTPUT);
}

void loop() {
  for (int ch = 0; ch < 4; ch++) {
    selectChannel(ch);
    int raw = analogRead(ADC_PIN);
    float voltage = raw * 3.3 / 4095.0;
    Serial.printf("Ch%d: %.2fV ", ch, voltage);
  }
  Serial.println();
  delay(100);
}

Platform Comparison Summary

Feature ESP32 Series Raspberry Pi Series
Type Microcontroller (MCU) Single Board Computer (SBC)
Processing Dual-core 240MHz ARM 700MHz-2.4GHz
Memory 520KB RAM, 4-16MB Flash 1-8GB RAM, SD storage
Operating System FreeRTOS (Real-time) Full Linux
ADC Channels Up to 20 built-in 3 (Pico only)
Power Consumption Very Low (10μA sleep) High (2-8W)
Connectivity WiFi + Bluetooth built-in WiFi/BT (Pi 3+), Ethernet
Programming C/C++, Arduino, MicroPython Python, C++, Java, Node.js
Real-time Performance Excellent Limited
Cost $2-10 $15-100

Use Case Recommendations

Choose ESP32 for:

  • IoT sensor networks - Built-in wireless connectivity
  • Battery-powered projects - Ultra-low power consumption
  • Real-time control systems - Deterministic timing
  • Cost-sensitive applications - Lower hardware cost
  • Simple to moderate complexity - Embedded programming
  • Wireless sensor nodes - WiFi/Bluetooth integration

Choose Raspberry Pi for:

  • Complex data processing - Full computing power
  • Web applications - Rich networking stack
  • Computer vision - Processing power for ML/AI
  • Database applications - Full Linux filesystem
  • Development flexibility - Multiple programming languages
  • Rich user interfaces - Desktop-like capabilities

Wiring Best Practices

Signal Conditioning

For 5V signals with 3.3V ADC:

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5V Signal ──[10kΩ]──●──[6.8kΩ]── GND
                    │
                    └── MCU ADC Pin

Noise Reduction

  • Add 100nF ceramic capacitors near sensors
  • Use twisted pair cables for long connections
  • Implement software filtering for stable readings
  • Ground all signal sources to common ground

Power Supply

  • Use stable 3.3V supply for sensors
  • Separate analog and digital grounds if possible
  • Add bulk capacitors (10-100μF) for power stability

High-Speed Sampling (ESP32 Advanced)

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#include "driver/adc.h"
#include "esp_adc_cal.h"

void setup() {
  Serial.begin(115200);
  adc1_config_width(ADC_WIDTH_BIT_12);
  adc1_config_channel_atten(ADC1_CHANNEL_1, ADC_ATTEN_DB_11); // GPIO2
  adc1_config_channel_atten(ADC1_CHANNEL_2, ADC_ATTEN_DB_11); // GPIO3
}

void loop() {
  // Fast sampling using low-level API
  int raw1 = adc1_get_raw(ADC1_CHANNEL_1);
  int raw2 = adc1_get_raw(ADC1_CHANNEL_2);
  
  Serial.printf("Raw1: %d, Raw2: %d\n", raw1, raw2);
  delayMicroseconds(100); // High-speed sampling
}

Conclusion

For 4+ channel analog input applications, ESP32-S3 is the recommended choice due to:

  • Abundant built-in ADC channels (20 available)
  • No need for external ADC components
  • Built-in wireless connectivity
  • Real-time performance capabilities
  • Cost-effective solution
  • Simpler hardware design

The ESP32 platform provides the optimal balance of features, performance, and cost for multi-channel analog input systems, especially when wireless connectivity and real-time processing are requirements.