ADC Differential Pi

The ADC Pi is an 8 channel 17 bit analogue to digital converter designed to work with the Raspberry Pi. The ADC Pi is based on two Microchip MCP3424 A/D converters each containing 4 analogue inputs. The MCP3424 is a delta-sigma A/D converter with low noise differential inputs.

Not sure which ADC you need ? Check our Analogue to Digital Buyers guide to compare our ADC expansion boards.

We designed the ADC Differential Pi as a companion for our ADC Pi. Unlike the ADC Pi the ADC Differential Pi does not include any voltage dividers so the inputs can be used to measure a differential voltage range of ±2.048V. This is useful for measuring inputs below ±2.048V or allows you to use your own voltage divider to measure higher voltages.

The ADC Pi is powered through the host Raspberry Pi using the GPIO port and extended pins on the GPIO connector allow you to stack the ADC Pi along with other expansion boards.

The two MCP3424 A/D converters communicate via i2c to the host Raspberry Pi giving you eight analogue inputs to use. A logic level converter is included on the ADC Pi board giving you a buffered 5V i2c port making it easy to add other I2C devices which operate at 5 volts without damaging the raspberry pi 3.3 volt i2c port. The i2c buffer uses N-channel mosfets with a maximum drain current of 100mA.

You will need to enable i2c on your Raspberry Pi, you can follow this tutorial to guide you through that process.

The I2C address bits are selectable using the on-board jumpers. The MCP3424 supports up to 8 different I2C addresses so with two A/D converters on each ADC Pi you can stack up to 4 ADC Pi boards on a single Raspberry Pi giving you 32 ADC inputs.

The MCP3424 contains a programmable Gain Amplifier giving the user a selectable gain of x1, x2, x4 or x8 before the analogue to digital conversion takes place.

The data rate for analogue to digital conversions is 3.75 (17 bit), 15 (15 bit), 60 (13 bit) or 240 (11 bit) samples per second. Data rate and resolution can be configured within software using the I2C interface.

We have a knowledge base article, ADC Sample Rate Comparison which has more detailed sample information and test scripts to compare the different MCP2424 ADC chip bit and sample rates.

Unused inputs should be tied to ground.

If you want to sample a higher input voltage you can use our ADC Pi Input Voltage Calculator to find the additional resistors and calculation values needed.

Note: We designed the ADC Differential Pi as a companion for our ADC Pi.  Unlike the ADC Pi the ADC Differential Pi does not include any voltage dividers so the inputs can be used to measure a differential voltage range of ±2.048V.  This is useful for measuring inputs below ±2.048V or allows you to use your own voltage divider to measure higher voltages.

Features

• 8 x 18-bit differential inputs
• Control via the Raspberry Pi I2C port
• Stack up to 4 ADC Differential Pi boards on a single Raspberry Pi
• Jumper selectable I2C addresses
• Buffered 5V I2C port
• Based on the MCP3424 from Microchip Technologies Inc
• Input range of ±2.048V
• On-board 2.048V reference voltage (Accuracy ± 0.05%, Drift: 15 ppm/°C)
• On-Board Programmable Gain Amplifier (PGA): Gains of 1, 2, 4 or 8
• Programmable Data Rate Options:
• - 3.75 SPS (18 bits)
• - 15 SPS (16 bits)
• - 60 SPS (14 bits)
• - 240 SPS (12 bits)
• One-Shot or Continuous Conversion Options

Specifications

• Vdd (5V pin on I2C bus): 5.0V
• ADC Input Voltage: -2.048V to + 2.048V
• Maximum ADC Input voltage: VSS–0.4V to VDD+0.4 V
• Current at Input Pins: ±2 mA
• I2C SDA/SCL voltage: 5.0 V
• I2C port current: 100 mA

Assembly Guide

The ADC Differential Pi is supplied with the 40 pin GPIO connector and the 12 pin address connector unsoldered. Before using the ADC Differential Pi you will need to solder both connectors onto the PCB.

We suggest soldering the 40 pin GPIO connector first and then the address select connector. Soldering the address select connector first will make it difficult to access the three corner pins on the GPIO connector. Assembly for the ADC Differential Pi is the same as on our ADC Pi Plus.

Documents

• ADC Differential Pi - 3D CAD File (STEP Format)
• Schematic Drawings
• Code Libraries and Demos
• Datasheets