The ADC Pi Zero is an 8 channel 17 bit analogue to digital converter designed to work with the Raspberry Pi Zero. The ADC Pi Zero 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.

Soldering required! This product comes unassembled and unsoldered.

We designed the ADC Pi Zero to work as a single ended A/D converter using the internal 2.048V reference voltage with the -V pins tied to ground. A voltage divider on the ADC Pi Zero board brings the input voltage range to a much more useful 0 – 5.06V. In this configuration the sample size is 17 bits for each channel.

Introduction:

The ADC Pi Zero is powered through the host Raspberry Pi Zero using the GPIO port and extended pins on the GPIO connector allow you to stack the ADC Pi Zero 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 Zero 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.

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 Zero you can stack up to 4 ADC Pi Zero boards on a single Raspberry Pi Zero giving you 32 ADC inputs.

The MCP3424 contains an on-board 2.048V reference voltage with an input range of ±2.048V differentially (full scale range of 4.096V/PGA). A programmable Gain Amplifier gives 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 Comparisonwhich 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.

I2C Address Selection

The MCP3424 analogue to digital converter contains two address select pins which can be tied to Vss, Vdd or left floating. This gives 8 possible I2C addresses for each chip. The ADC Pi Zero contains two MCP3424 chips so you can stack up to 4 ADC Pi Zero boards on a single Raspberry Pi. To simplify address selection on the ADC Pi Zero we have included a set of address selection pins which can be configured using the included jumpers. The illustrations below show the four recommended configurations for your ADC Pi Zero and the associated I2C addresses.

Note:
Disconnect the ADC Pi Zero from the Raspberry Pi before changing the address pins. You may need to short the 5V and ground with a resistor to discharge the capacitors in order for the new addresses to be recognised.

Address selection pins

I²C Address Table

Adr 0	Adr 1	I2C Address
Low or Float	Low or Float	0x68
Low	Float	0x69
Low	High	0x6A
Float	Low	0x6B
High	Low	0x6C
High	Float	0x6D
High	High	0x6E
Float	High	0x6F

Warning

Do not under any circumstanced connect the two centre pins together. This will create a direct short between the 5V and ground pins and will damage or destroy your Raspberry Pi and ADC Pi Zero board.

Recommended Address Configurations

Configuration 1:

Analogue Channels 1-4 = I2C Address: 0x68
Analogue Channels 5-8 = I2C Address: 0x69

Address Configuration 1

Configuration 2:

Analogue Channels 1-4 = I2C Address: 0x6A
Analogue Channels 5-8 = I2C Address: 0x6B

Address Configuration 2

Configuration 3:

Analogue Channels 1-4 = I2C Address: 0x6C
Analogue Channels 5-8 = I2C Address: 0x6D

Address Configuration 3

Configuration 4:

Analogue Channels 1-4 = I2C Address: 0x6E
Analogue Channels 5-8 = I2C Address: 0x6F

Address Configuration 4

Datasheets

MCP3424

Compatibility Chart

Raspberry Pi Model A	No
Raspberry Pi Model B	No
Raspberry Pi 1 Model A+	Yes
Raspberry Pi 1 Model B+	Yes
Raspberry Pi 2 Model B	Yes
Raspberry Pi 3 Model B	Yes
Raspberry Pi Zero	Yes
ODroid C1	Yes
ODroid C2	Yes

Features

8 x 17-bit 0 to 5V Single Ended Inputs
Control via the Raspberry Pi I2C port
Stack up to 4 ADC Pi Zero boards on a single Raspberry Pi
Jumper selectable I2C addresses
Buffered 5V I2C port
Based on the MCP3424 from Microchip Technologies Inc
Single Ended full-scale range of 5.0V
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 (17 bits)
- 15 SPS (15 bits)
- 60 SPS (13 bits)
- 240 SPS (11 bits)
One-Shot or Continuous Conversion Options

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

Input Ratings & Specifications

Vdd (5V pin on I2C bus)	5.0V
All AD inputs and outputs	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

Board Layout

Schematic

Click to download schematic PDF.

Mechanical Drawings

Click image to enlarge

Sample Code

We have Arduino, C, Windows 10 IOT, Python 2 and Python 3 libraries available for this expansion board. You can download all of the libraries from github at:

https://github.com/abelectronicsuk/

Download the Arduino librariesfrom: https://github.com/abelectronicsuk/ABElectronics_Arduino_Libraries

To download the C libraries to your Raspberry Pi type in terminal:

git clone https://github.com/abelectronicsuk/ABElectronics_C_Libraries.git

To download the Python 2 libraries to your Raspberry Pi type in terminal:

git clone https://github.com/abelectronicsuk/ABElectronics_Python_Libraries.git

To download the Python 3 libraries to your Raspberry Pi type in terminal:

git clone https://github.com/abelectronicsuk/ABElectronics_Python3_Libraries.git

Download the Windows 10 IOT libraries from:https://github.com/abelectronicsuk/ABElectronics_Win10IOT_Libraries/

Tutorials

We have a range of tutorials for the ADC Pi, ADC Pi Zero and ADC Pi Plus in our Knowledge Base

ADC Pi Zero Tutorials

Assembly Instructions

The ADC Pi Zero is supplied with the 40 pin GPIO connector and the 12 pin address connector unsoldered. We supply the ADC Pi Zero this way because the Raspberry Pi Zero is also supplied without a GPIO header and the ADC Pi Zero could therefore be fitted both above or below the Raspberry Pi Zero.

Before using the ADC Pi Zero 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.

PCB Header Assembly Jig

Download and print our PCB Header Assembly Jig to hold your circuit board when soldering the header pins.

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