Arduino Mega Expansion board

A mini shield-like add-on for the Arduino Mega designed to add wifi/Bluetooth connectivity and more alongside the standard Uno-sized shield.

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I have a few project ideas which all revolve around a display, plenty of io, and wifi access.
In order to help me work on these projects I have been trying to assemble a 'test platform' for me to work on my code while I await parts/plan assembly for the main projects.

I wanted to keep this test platform ultra-simple to assemble; off-the-shelf components and ready-made shields, just so it's easy to put together.
To facilitate that i chose my Arduino Mega as the base; plenty of memory to play with for sketches, compatible with Arduino Uno shields (such as the LCD shield I am using in a lot of projects), and has plenty of pin availability even with the shield plugged in (a selection of digital and analog pins, in addition to the extra serial ports and i2c pins - awesome for interfacing with other devices).

Now I need to put together a small board to get rid of the rat's nest of wires!

The board I want to create will simply plug into the pins available while a standard Arduino Uno format shield is plugged in:

  • D16-D21 on one side
  • A8-A15 on the other side
  • All even pins from D22-52 on double row
  • 5v/GND pins at the top of double row.

As well as allowing the board to be securely plugged in these pins can be utilised on the board itself for connections.

So far here's what I envisage being on the board:

Analog Pins

These pins will be brought out onto a header to allow easy interfacing with analog sensors, buttons etc. Ideally a 5v and gnd pin would accompany the Analog pins, but given how small this board will be it may not be feasible.

Digital Pins

in the same format as the Analog pins, but using a different colour header to avoid confusion. Not all pins would be brought out due to space constraints, but possible an unpopulated header could be included for those.


WiFi is a must; a lot of my projects planned utilise an ESP8266 to either host a mini webserver or just to pass data via websockets etc.

In my prototype of this board I will most likely use a Wemos D1-mini as I have a few lying around. Eventually, if i design a PCB, I will look for a most suitable option.

In order to fit everything on this little board I will test placing the Wemos board on the underside of the board, sitting between the board and the Mega itself.

Serial pins TX1/RX1 will be used for communication with the ESP8266.

I may also connect the i2c pins for this too, to allow direct interfacing with the Wemos for externally connected devices.

Bluetooth/Serial port

Bluetooth is not going to be necessarily required in every prototyping environment I'd like to use this with, however it is something I'd like to be neatly included should it be required.

a 4-pin female header header to allow the plugging in of a Bluetooth module (or serial cable or other serial device) will be included, connected to TX2/RX2 for communication with the Mega.


i2c is a standard that I'd like to use with this project; the ability to easily integrate extra devices (such as additional lcd screens, other microcontrollers etc) is ideal for creating a flexible platform to work on. I will add a few headers for easy connection of 2-4 devices. I may look different connectors other than the standard pins (such as grove-style connectors) to give a nice easy way of wiring up devices.

  • 1 × ESP8266 For WiFi connectivity via TX1/RX1 pins
  • 1 × Bluetooth Module For serial connection via TX2/RX2 pins
  • 1 × Male pin headers For connecting the add-on board to Mega & sensor pins
  • 1 × Female pin headers For connecting ESP8266/Bluetooth etc
  • 1 × Perfboard For cutting down to make the add-on board

  • PCB Design skillz required

    Craig Hissett06/13/2017 at 13:18 0 comments

    Apologies for the lack of updates on this project.

    I'm still looking to find the time to invest in learning how to draw up a schematic and how to design a pcb.

    Once that's done I can get the board ordered and soldered up ready to go.

    I can't bloody wait to get this working!

  • Board Design ideas

    Craig Hissett05/02/2017 at 15:46 5 comments

    Having semi-finalised the idea in my head I thought it was time to take a note of it, before I forget or change my mind again :-)

    Here's what I have come up with:

    This is a very primitive drawing done using Microsoft Paint so please excuse the roughness of it.

    The board will fit over the lower end of the Mega, plugging into the communication pins, digital pins and analog pins. The mounting holes are there for guidance.

    The ESP8266 & Bluetooth modules will be soldered underneath, overlapping the board somewhat. The overhang would fit under the arduino shield mounted alongside it.

    On the top there are banks of pins:

    • 4x4: i2c pins (SDA, SCL, 5v, GND)
    • 8x3, 8x3: Digital Pins (D22-D52 even pins, 5v/3.3v, GND)
    • 8x3: Analog Pins (A8-A15, 5v, GND)

    I would also like to add the option to connect an external power source to help power all the potential extra devices if necessary.

    If anyone is interested in helping me produce a board that would be greatly appreciated! ( @davedarko, nudge nudge, wink wink ;-) ) that would be amazing!


  • Wifi Serial

    Craig Hissett04/24/2017 at 19:21 0 comments

    So, delivery #1 of many arrived today; 3 ESP07-based serial boards.

    With only Tx, Rx, power and ground pins broken out, this board is controlled via AT and over a serial connection.

    This is perfect for this project - added to the Serial1 port of the Mega it will make wifi comms easy!

    I am going to adapt the Arduino sketch of the project I previously shared to process an 'ESP_' command, and forward the following string (which will be the AT command) straight to Serial1.

    In addition I am going to write a python based GUI, along the lines of the previous link's C# application. This is to practice writing python GUI apps, and also to write something that works cross platform.

    Will post my results Tommorrow, all being well!

  • Look at this!

    Craig Hissett04/22/2017 at 15:51 0 comments

    still waiting on a few bits and bobs to start putting together my projects, so started thinking about perhaps creating software to accompany this device, and making its use simple.

    Found this little beauty, which will enable a fantastic start!


  • ESP Spree!

    Craig Hissett04/03/2017 at 15:00 0 comments

    That monthly sacred day known as Pay Day has arrived.

    I've ordered a few different types of ESP8266 based boards for my various projects:

    The board I have ordered is nice and slim, and only has the serial port pins (tx/rx/5v/gnd) broken out. This is perfect for this as I can simply add a rightangled female header and plug this board in to keep a really low profile under the board. I've always planned on connecting the serial pins up to TX1/RX1 on the mega so there's no need for any other headers.

    Good times!

  • Rough layouts for boards

    Craig Hissett03/22/2017 at 18:17 1 comment

    Just at work so had to use Excel to map my plans before I forgot ha ha!

    Row 8 details the header for the Wemos D1 mini, and where it will sit on my perfrboard in relation to the Mega pins. It shall be mounted underneath, keeping the top free for Analog, Digital and i2c headers.

    TX1 and RX1 go straight to the RX and TX pins of the D1 mini, with the SDA and SCL lines routed to meet pins D2 and D1 on the Wemos board.

    5v and ground lines are added to the left of the board where no other pins are connected.

    As you can see the 5v and the Ground pins of the Wemos will stick out underneath the board, but that is fine; in order to remove it you will need to remove the arduino shield first, and to install it you will have to plug in the expansion board first.

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