Expander Pi

GPIO, Analogue and RTC Expander for the Raspberry Pi

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Features:

  • 16-channel digital input/outputs
  • 8-channel 12-bit resolution analogue input (ADC)
  • 2 channel 12-bit resolution analogue output (DAC)
  • Real-time Clock (RTC) with CR2032 battery holder.

Expander Pi is a versatile digital and analogue development board for the Raspberry Pi and other compatible single-board computers. It allows you to connect to switches, lights, sensors, and many other devices, allowing you to communicate with the outside world.

The Expander Pi plugs into the GPIO port on your Raspberry Pi and can be securely fitted to the Raspberry Pi using the optional mounting kit. It is powered through the host Raspberry Pi using the GPIO port or the onboard power connector. Extended pins on the GPIO connector allow you to stack the Expander Pi and other development boards.

Using the Expander Pi, you can connect 8 analogue inputs, 2 analogue outputs and 16 digital inputs or outputs to your Raspberry Pi. The Expander Pi also features an onboard Real Time Clock (RTC) to ensure that your Raspberry Pi always has the correct date and time.

Mounting holes are provided so you can securely bolt the Expander Pi to your Raspberry Pi with our mounting kit (sold separately).

The 16 input and output channels, using the MCP23017 16-bit I/O expander from Microchip Technology Inc, can be independently configured as either inputs or outputs with a maximum input of 5 volts on each channel.

The 2-channel digital-to-analogue converter is a 12-bit resolution using Microchip MCP4822 dual channel 12-bit DAC with an internal voltage reference.

The 8 analogue to digital converter is a 12-bit resolution using a Microchip MCP3208 8-Channel 12-Bit A/D Converters with SPI Serial Interface with a maximum sample rate of 100 ksps and includes a 4.096 volt precision voltage reference. Many of the Raspberry Pi ADC boards on the market use the 10 bit MCP3008 analog to digital converter (ADC). A 12-bit ADC provides 4 times the resolution of a 10-bit ADC, allowing for finer granularity when converting an analogue signal into its digital representation.

Please note the maximum sample rate is dependent on the programming language used and the CPU speed and usage. A separate Vref pin is included allowing you to use an external voltage reference. If you use an external voltage reference, you must disconnect the onboard voltage reference IC by removing the solder bridge from jumper J1. Failing to remove the J1 solder bridge when using an external reference could cause damage to the onboard voltage reference or your external reference circuitry.

The Real Time Clock uses the DS1307 RTC real-time clock and a CR2032 battery to maintain the date and time when the main system power is unavailable.

Warning: Do not connect the Expander Pi to your Raspberry Pi when the power is connected without a CR2032 battery installed. This can cause damage to the DS1307 RTC chip.

The Expander Pi uses a CR2032 button battery (battery not included).

Due to the use of the SPI bus and fixed addresses on the I2C bus, the Expander Pi can not be stacked alongside the ADC DAC Pi Zero or RTC Pi.  Only one Expander Pi can be used on a Raspberry Pi.

The I2C address for the MCP23017 digital I/O chip is set to 0x20; if you use the Expander Pi with an IO Pi Plus/Zero, you will need to ensure the addresses for the IO Pi chips are not set to 0x20.

Suppose you want to power the Raspberry Pi from the USB connector and use a separate supply for powering the Expander Pi. In that case, we recommend removing the solder bridge "JUMPER" next to GPIO pin 1 on the Expander Pi, disconnecting it from the Raspberry Pi 5V pins.

Note for MCP4822 LDAC pin: The Expander Pi is supplied with the LDAC pin on the MCP4822 DAC connected to ground, disabling the LDAC functions. The LDAC pin can be connected to the GPIO 25 pin on the Raspberry Pi GPIO header by removing resistor R3 and bridging the pads on R4 with solder or a 0R resistor.

Note for MCP23017 IO Controller: Microchip recommends that pin 8 (GPA7) and pin 16 (GPB7) are used as outputs only.  This change was made for revision D MCP23017 chips manufactured after June 2020. See the MCP23017 datasheet for more information.

Note for changes in version 2.1:

  • U3 74HC4050D was replaced with a TXB0108PWR. U3 is used for level shifting the SPI bus from 3.3V on the Raspberry Pi to 5V.
  • Resistors R3 and R4 were added to allow the LDAC pin on the MCP4822 to be connected to ground or GPIO25 on the Raspberry Pi GPIO header.
  • The schematic for version 2.0 can be viewed here.

Legacy Expander Pi Versions

See our Knowledge Base article for previous versions of this board.

Technical Details

Ratings & Specifications

Digital IO:

Vdd (isolation jumper removed):
4.5V - 5.5V
Voltage at I/O Pins:
0 - Vdd
Current at I/O Pins (sourced or sunk):
25 mA
Maximum current on all I/O pins combined:
125 mA

ADC Inputs:

Maximum ADC Input Voltage when using on-board voltage reference:
4.096V
Maximum ADC Input Voltage when using an external voltage reference:
5V
Maximum External Reference Voltage:
5V
Analogue input type:
single-ended or pseudo-differential pairs
All inputs and outputs w.r.t. VSS:
-0.6V to VDD +0.6V
Max ADC Sample Rate:
100,000 samples per second
Under Python 2.7 on a Pi 3+: 4400 samples per second.

DAC Outputs:

Maximum output voltage at Gain 1:
2.048V
Maximum output voltage at Gain 2:
4.096V
Maximum output current:
25 mA

3D CAD Model

Expander Pi - 3D CAD File (STEP Format)

Schematic

Expander Pi Schematic
Download the schematic PDF.

Mechanical Drawings

Compatibility

The Expander Pi uses the SPI port and I2C addresses 0x20 and 0x68; please ensure that any additional development boards do not have an address conflict with these I2C addresses.  

Please follow our tutorials for enabling I2C and SPI before using the Expander Pi on your Raspberry Pi.

The Expander Pi can be stacked with the following boards.

  • 1-Wire Plus / Zero
  • ADC Pi (i2c address needs to be changed using selection jumpers)
  • ADC Differential Pi (i2c address needs to be changed using selection jumpers)
  • I2C Switch
  • IO Pi Plus / Zero (i2c address needs to be changed using selection jumpers)
  • IO Zero 32 (i2c address needs to be changed using selection jumpers)
  • RS485 Pi
  • Servo PWM Pi
  • Serial Pi Plus / Zero

The Expander Pi is not compatible with the following boards:

  • ADC DAC Pi Zero
  • RTC Pi Plus / Zero

We have tested the Expander Pi on the following platforms.

Model Status
Raspberry Pi Model A / B
Raspberry Pi 1 Model A+ / B+
Raspberry Pi 2 Model B
Raspberry Pi 3 Model A+ / B / B+
Raspberry Pi 4 Model B
Raspberry Pi 5
Raspberry Pi Zero
Raspberry Pi Zero W / Zero 2 W
Raspberry Pi Compute Module 4 IO Board
Raspberry Pi 400
Asus Tinker Board

Assembly Instructions

The Expander Pi is supplied with the 40-pin GPIO connector, and the CR2032 battery connector unsoldered. 

Before using the Expander Pi, you must solder both connectors onto the PCB.  We suggest soldering the 40-pin GPIO connector first and then the battery connector.  Soldering the battery connector first will make it challenging to access some of the pins on the GPIO connector.

Assembly Guide Video

Watch our assembly guide on YouTube. (opens in a new window)

PCB Header Assembly Jig

Our PCB Header Assembly Jig holds your circuit board when soldering the header pins.

Code Libraries and Tutorials

This development board has Python, C, C++, Node.js and Windows 10 IOT libraries.  All of our software libraries are open source and can be download from our GitHub repository or by clicking on the logos below for your selected programming language.

Expander Pi Articles & Tutorials

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Important Information

This development board/kit is intended for use for ENGINEERING DEVELOPMENT, DEMONSTRATION, OR EVALUATION PURPOSES ONLY and is not considered by abelectronics.co.uk to be a finished end-product fit for general consumer use. As such, the goods being provided are not intended to be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including product safety and environmental measures typically found in end products that incorporate such semiconductor components or circuit boards. Persons handling the product(s) must have electronics training and observe good engineering practice standards. This development board/kit does not fall within the scope of the European Union directives regarding electromagnetic compatibility, restricted substances (RoHS), recycling (WEEE), FCC, CE or UL, and therefore may not meet the technical requirements of these directives or other related directives. Note: documents in Portable Document Format (PDF) require Adobe Acrobat Reader 5.0 or higher to view, download Adobe Acrobat Reader or other PDF reading software for your computer or mobile device.

Shipping and Delivery

For orders under £35 and tracked orders, the following delivery charges apply.

Shipping Rates

United Kingdom

Service Cost  Estimated Delivery Time 
Royal Mail 1st Class £2.49 1 - 3 days (Mon - Sat)
Royal Mail Special Delivery (Tracked) £8.49 Next day (Mon - Sat)

European Union

Deliveries to: Austria, Belgium, Bulgaria, Croatia, Republic of Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain and Sweden. 

Service Cost  Estimated Delivery Time 
Royal Mail Airmail Service £4.29 3-5 Working Days **
Royal Mail International Tracked and Signed £12.99 3-5 Working Days **

Rest of the World

Service Cost  Estimated Delivery Time 
Royal Mail Airmail Service £5.99 5-7 Working Days **
Royal Mail International Tracked and Signed £18.99 5-7 Working Days **

* Free delivery uses the Royal Mail 1st Class service for UK orders and Royal Mail Airmail Service for international orders.

** All International destinations are subject to customs clearance at the destination country, which can add a short delay to your delivery times. Additional import duty may be charged for your order by customs on arrival to your country based on the order value.

We have a full list of all available delivery destinations on the Shipping Country List.

We aim to dispatch your order within 1 working day.  

Working days are normal weekdays; dispatch times do not include Saturdays, Sundays and national holidays. Delivery transit times do not include national holidays and Sundays but may include Saturdays, depending on the delivery service provider in the destination country.

You can view details of international shipping issues and delays with the Royal Mail airmail service at Royal Mail International Incident Bulletin.

You can check the status of your order by going to the My Account area of the website.

Import One-Stop Shop (IOSS) FAQ

What is the Import One-Stop Shop (IOSS)?

The Import One-Stop Shop (IOSS) is a system introduced by the European Union to simplify VAT collection for goods valued at €150 or less that are shipped to customers in the EU from outside the EU. By using IOSS, sellers collect VAT at the point of sale, ensuring that buyers do not have to pay additional import taxes or customs fees upon delivery.

How does IOSS benefit me as a customer?

IOSS makes your shopping experience easier and more transparent by:

Including VAT in the purchase price you see at checkout.

Eliminating unexpected customs charges or fees upon delivery.

Reducing potential delivery delays caused by customs clearance.

Will I have to pay any additional charges when my order is delivered?

No. If your order is covered by IOSS, all applicable VAT and import charges are already included in the price you pay at checkout. There will be no additional charges when your order is delivered.

How do I know if my order is covered by IOSS?

All orders shipped to EU countries and valued at €150 or less are covered by our IOSS registration. If your order qualifies, the VAT and import fees will be automatically calculated and included in the total price during checkout.

Does IOSS apply to all products?

IOSS applies to goods valued at €150 or less that are shipped from outside the EU to customers in EU member states. Certain items, such as excisable goods (e.g., alcohol or tobacco), may not qualify for IOSS coverage.

What happens if my order exceeds €150?

For orders valued above €150, IOSS does not apply. In such cases, import VAT and any applicable customs duties will need to be paid separately, usually upon delivery. We recommend checking your local regulations for further details.

Do I need to do anything to use IOSS?

No action is required on your part. We handle all the necessary IOSS processes on our end to ensure your order is VAT-compliant and free from additional import fees.

Does IOSS reduce delivery times?

Yes, IOSS can help speed up delivery times by streamlining the customs clearance process. Since VAT is prepaid, your order is less likely to be delayed during customs inspections.

Is IOSS available in all EU countries?

Yes, IOSS applies to all EU member states. Regardless of where you are in the EU, you can enjoy the benefits of IOSS when shopping with us.

Can I claim VAT back if I am VAT registered in the EU?

If you are VAT registered in the EU and wish to claim VAT back, please use the Guest Checkout and enter your VAT registration details before placing your order. It is not possible to enter your VAT details when using the PayPal express checkout.

What should I do if I still have questions?

If you have any further questions about IOSS or your order, feel free to contact our customer support team. We’re here to help!

Delivery Duty Unpaid for orders sent outside of the United Kingdom and EU over 150 euros

All orders sent to countries other than the United Kingdom and EU over 150 euros are shipped on a DDU (Delivery Duty Unpaid) basis, and the recipient may be subject to local taxes and customs import duty, which is charged on the value of the order.

Payment of these fees is the sole responsibility of the customer. 

Order Tracking

Our standard shipping service is not tracked, and we cannot supply tracking information for your order.

We can offer alternative shipping using Royal Mail, tracked and signed for service. You can select this option at checkout. Please note full end-to-end tracking depends on the tracking service from the regional postal service in the destination country.

Once your order has been sent, you can view your tracking code, which is available in the My Account section. Please allow up to 72 hours for your tracking code to be added to your order after despatch.

Returns

Our 180-day returns guarantee means that if for any reason you are unhappy with your purchase, you may return it to us in its original condition within 180 days of the date you received the item, unopened (with any seals and shrink-wrap intact), and we will issue a full refund for the price you paid for the item. We can only accept the return of opened items if they are faulty.

All Raspberry Pi add-on boards are checked on a Raspberry Pi during production, and all inputs are checked to ensure the inputs and outputs are within the specified ratings.

We cannot accept returns for faults caused by over-voltage being applied to inputs on the boards by the purchaser.

When returning an item to us, please clearly state why you are returning your parcel and whether you require a refund or exchange. Please note that the parcel is your responsibility until it reaches us, so we recommend you send it via registered or recorded post. 

The time it takes for a refund to reach the customer depends on the banks involved. It would normally take 3 - 5 working days to complete it.

Sales Tax

United Kingdom VAT at 20% is added to all orders for UK destinations. VAT is not added to NON-UK and EU destinations where the order total is more than 150 euros.

We are not responsible for any import taxes or VAT on the orders in the destination country. Import duty/tax is always paid by the person/company receiving the parcel/order.

Removed Delivery Destinations

We regret that we had to remove the following countries from our delivery destinations due to a very high failure rate of our parcels being delivered using the Royal Mail airmail service. This resulted in us refunding all of the missing orders, and we cannot continue to make such large losses by sending parcels to destinations where a large percentage of the items are lost in the postal systems.

Brazil, China, Israel, Mexico, Saudi Arabia, Singapore, Sri Lanka, Taiwan, Turkey, USA (due to shipping tariffs)  and the United Arab Emirates.

Also, due to problems with the courier delivering parcels to these destinations, we cannot use a third-party courier service for these delivery destinations due to the extra costs involved.

Customers can purchase our products from one of our international resellers

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