Raspberry Pi Hardware Guide

Complete parts list and assembly guide for the Raspberry Pi-based Open Colorimeter.

Overview

The Raspberry Pi version provides a web-based interface accessible from any device on your network. No physical display required - control everything through your phone, tablet, or computer.

Estimated Cost: $200-250

Required Components

Core Controller

Component Description Source Est. Cost
Raspberry Pi 3/4/5 Main controller Adafruit, Amazon $35-75
MicroSD Card 16GB+ for OS and data Amazon $8-15
USB-C Power Supply 5V 3A for Pi Adafruit $8

Recommendation: Raspberry Pi 4 (4GB RAM) or Pi 5 for best performance. Pi 3 works but may be slower.

I2C Hardware

Light Sensor

Component Description Adafruit PID Est. Cost
TSL2591 Light Sensor High-sensitivity light-to-digital converter 1980 $6.95

I2C Address: 0x29 (default)

Features:

  • 600M:1 dynamic range
  • Programmable gain (1x, 25x, 428x, 9876x)
  • Integration time: 100ms to 600ms
  • IR + visible light measurement

Motor Control

Component Description Adafruit PID Est. Cost
DC & Stepper Motor HAT 4-channel DC motor controller 2348 $22.50
12V DC Power Supply 12V 2-3A for motors 798 $12.50

I2C Address: 0x60 (PCA9685), 0x70 (auxiliary)

Features:

  • 4 H-Bridges for DC motors
  • 1.2A per channel continuous
  • Stackable design
  • Separate motor power supply

Solenoid Control

Component Description Adafruit PID Est. Cost
I2C 8-Channel Solenoid Driver MCP23017-based valve controller 6318 $9.95
12V Solenoid Valves Normally closed air valves (qty varies) 4663 $5.95 each

I2C Address: 0x20 (default, configurable)

Features:

  • 8 independent channels
  • 12V operation
  • LED status indicators per channel
  • Shared I2C bus with other components

Motors & Actuators

DC Motors

Component Description Source Est. Cost
Peristaltic Pump Motors 12V DC motors with pumps Various $15-30 each
Small DC Motors 6-12V for stirring/mixing Adafruit, Amazon $5-10 each

Requirements:

  • Voltage: 4.5V - 13.5V
  • Current: < 1.2A continuous per motor
  • Quantity: 2-4 motors depending on application

Typical Configuration:

  • Motor 1: Sample pump (fill cuvette)
  • Motor 2: Reagent pump (dosing)
  • Motor 3: Stirrer/mixer (optional)
  • Motor 4: Waste pump (optional)

Fluidics Components

Tubing & Connections

Component Description Adafruit PID Est. Cost
Silicone Tubing 3mm ID, food-safe 4661 $5.95/meter
Tube Fittings Barb connectors, valves Various $10-20

Cuvette & Optics

Component Description Source Est. Cost
Optical Cuvette 1cm path length, 3.5mL Amazon, Lab suppliers $10-20
LED Light Source 525nm (green) or 880nm (NIR) Adafruit $5-10

Cuvette Requirements:

  • Material: Optical-grade plastic or quartz
  • Path length: 1 cm (10mm)
  • Volume: 3-5 mL
  • Clear/transparent walls

Power Requirements

Power Distribution

Power Rail Voltage Current Usage
Raspberry Pi 5V 2-3A USB-C power adapter
Motors 12V 2-3A Motor HAT green terminal
Solenoids 12V 1-2A Solenoid driver terminal

Important:

  • Motor power is separate from Raspberry Pi power
  • Never connect 12V motor power to Raspberry Pi GPIO
  • Use proper polarity (+ and -)
  • Raspberry Pi: Official USB-C 5V 3A power supply
  • Motors: 12V 2A+ barrel jack adapter (Adafruit #798)
  • Total System: ~15W during operation

Assembly Overview

1. Stack the Motor HAT

  1. Power off Raspberry Pi
  2. Align Motor HAT with 40-pin GPIO header
  3. Press firmly to seat all pins
  4. HAT should sit flush on top

2. Connect I2C Devices

All I2C devices share the same SCL/SDA bus:

Connections:

  • TSL2591 Sensor:
    • VIN → Pi 3.3V or 5V
    • GND → Pi GND
    • SCL → Pi GPIO 3 (SCL)
    • SDA → Pi GPIO 2 (SDA)
  • Solenoid Driver:
    • VIN → Pi 3.3V or 5V
    • GND → Pi GND
    • SCL → Pi GPIO 3 (SCL)
    • SDA → Pi GPIO 2 (SDA)

Note: All I2C devices can connect to the same pins via breadboard or I2C hub.

3. Connect Motors

Connect DC motors to Motor HAT blue terminal blocks:

  • M1, M2, M3, M4 - two wires per motor
  • Polarity determines direction (can swap if backwards)

4. Connect Motor Power

Connect 12V power supply to Motor HAT green terminal:

  • + (positive) to + terminal
  • - (ground) to - terminal

Warning: Do NOT connect 12V to Raspberry Pi GPIO!

5. Connect Solenoids

If using solenoid valves:

  1. Connect 12V power to solenoid driver
  2. Connect valves to channels 1-8
  3. Each valve requires two wires

I2C Address Reference

Device Address Configurable
TSL2591 Sensor 0x29 No
Motor HAT (PCA9685) 0x60 Yes (solder jumpers)
Motor HAT (auxiliary) 0x70 No
Solenoid Driver (MCP23017) 0x20 Yes (solder jumpers)
Multiplexer (TCA9548A) 0x70 Yes (avoid conflict)

Verify I2C Devices:

sudo i2cdetect -y 1

Should show devices at their respective addresses.

Bill of Materials Summary

Minimum System (Sensor Only)

Component Qty Est. Cost
Raspberry Pi 4 (4GB) 1 $55
MicroSD Card (32GB) 1 $10
USB-C Power Supply 1 $8
TSL2591 Sensor 1 $7
Total   ~$80

Full System (Motors + Solenoids)

Component Qty Est. Cost
Raspberry Pi 4 (4GB) 1 $55
MicroSD Card (32GB) 1 $10
USB-C Power Supply 1 $8
TSL2591 Sensor 1 $7
Motor HAT 1 $23
12V Power Supply (motors) 1 $13
DC Motors 2-4 $40-80
Solenoid Driver 1 $10
Solenoid Valves 4 $24
Tubing & Fittings - $20
Cuvette 1 $15
LEDs 2 $10
Total   ~$235-275

Optional Enhancements

Sensor Multiplexer (Multi-Sensor Support)

Component Description Adafruit PID Est. Cost
TCA9548A Multiplexer 8-channel I2C switch 2717 $6.95

Use Case: Connect multiple TSL2591 sensors for different wavelengths or tests.

Configuration: Set I2C address to 0x71 or other to avoid conflict with Motor HAT auxiliary chip (0x70).

Enclosure & Mounting

  • 3D printed enclosure (STL files coming soon)
  • DIN rail mounting brackets
  • Acrylic or aluminum case
  • Cable management and strain relief

Next Steps

  1. Order Components: Use Adafruit shopping cart with PIDs listed above
  2. Install Software: See Raspberry Pi Setup Guide
  3. Assemble Hardware: Follow connection diagrams above
  4. Test I2C: Verify all devices detected with i2cdetect
  5. Configure System: Edit mappings.json for device names
  6. Calibrate: Create calibration curves for your tests

Troubleshooting

Motor HAT Not Detected

Check:

  • HAT properly seated on GPIO pins
  • I2C enabled in raspi-config
  • Run sudo i2cdetect -y 1 to scan bus

Motors Not Running

Check:

  • 12V power connected to green terminal
  • Polarity correct (+ and -)
  • Motor wires secure in blue terminals
  • Try swapping motor wires if direction is backwards

Sensor Not Found

Check:

  • Wiring: VIN, GND, SCL, SDA
  • Voltage: 3.3V or 5V (both work)
  • Address: Should appear at 0x29

Resources

Ready to build? Continue to Raspberry Pi Setup Guide