Analogue to digital converter Buyers Guide
Choosing an analogue to digital converter
Created: 03/10/2015 | Last Updated: 22/05/2021
We sell a range of analogue to digital expansion boards for the Raspberry Pi which can also be used on other platforms such as Arduino.
This guide is to help you choose the best ADC board for your application.
When selecting an ADC you need to consider the characteristics of the ADC for your needs.
- Input voltage range - Many analogue to digital converters have a single ended input range of 0 to 2.048 volts or a differential input range of -2.048 to + 2.048
- Interface - ADC chips will either use I2C or SPI bus interfaces. SPI is faster but you are limited by the number of devices the SPI bus can accept. I2C is slower but you can connect many more devices to the I2C host machine
- Number of channels - this is the number of voltage inputs you can connect to the boards.
- Sensitivity - The sensitivity of an ADC chip is measured by its bit rate. A higher bit rate means that the chip has a higher resolution for measuring the input voltage but this comes at the expensive of the speed of the readings. Our ADC boards have bit rates of between 12 bit and 18 bit.
- Sample Rate - This is the speed in which the ADC chip can sample and report the input voltage. The ADC DAC Pi can sample several thousand times per second whereas the ADC Pi & ADC Differential Pi can sample between 3.5 (18-bit mode) and 120 (12-bit mode) samples per second on each input channel but at a higher resolution than the faster ADC DAC Pi boards.
How many inputs do you need to measure?
Up to two inputs:
The ADC DAC Pi Zero is a 2 channel 12-bit high speed analogue to digital converter which measures between 0 and 3.3 Volts
More than two inputs:
Do you need to read a positive voltage between 0 and 5 volts?
The ADC Pi is an 8 channel 17 bit analogue to digital converter which measures between 0 and 5 Volts using its onboard voltage divider. They can be stacked to give you up to 32 analogue inputs.
Do you need to be able to read a differential voltage inputs and/or single ended inputs?
ADC Differential Pi is an 8 channel 18 bit analogue to digital converter which allows you to measure an input range of -2.048 volts to + 2.048 volts on each channel. Each channel can also be used in single-ended mode by connecting the negative side of the input to the GND pads. The ADC chip will then measure an input range of 0 to 2.048 volts which you can then expand the input range using an external resistor voltage divider.
Expanding the ADC Pi input voltage range.
The ADC Pi Plus and ADC Pi Zero use resistor voltage dividers on each input using 10k and 6K8 values to reduce inputs down to a voltage suitable for the ADC chip. By default the input voltage can be a maximum of 5.06V but this can be increased by adding a resistor in series with the input.
We have a calculator you can use to find the correct resistor value for your voltage range.