Summary

So I needed more Arduino memory for a brewery controller project that I parked in 2011. Originally I was using an Arduino Uno which was well up to the job. Then I added to the code and now the compiler tells me it has all but filled the memory available at run time.

The Arduino mega, the next logical step up, has 54 IO pins and 4x as much memory as the Uno and is huge. When I looked for a bare bones kit list/design it clearly won't be possible as the MCU is a QFN (quad-flat no-leads) package and not available in a DIP (dual in-line) package version. There are conversion kits out there which package a QFN Atmel 2560 onto a DIP board which then can be plugged into a DIP Uno board instead of a DIP Atmel328P MCU, but they don't work for my Uno's as mine all have QFN chips so no DIP socket.

Price was another thing - the 2560 adapter could be used to make a bare bones version, at around £10 plus the other components.

So a bit more digging and i found the 'Arduino Mega 2560 PRO MINI Embedded' board (if you go looking for it be careful, there are 2 very similar versions, one with the CH340G usb interface and one without)

This is the listing I bought from: https://www.ebay.co.uk/itm/Arduino-Mega-2560-PRO-MINI-Embedded-MCU-ATmega2560-USB-CH340G-In-SS/183504694790 - I got 5 for £36.55 inc delivery, so £7.31 each.

I soldered headers onto 2, one set up with the pins on the top of the board and one set down with the pins on the underside of the board.

My jumper wires were very loose on the pins and neither my eyes nor fingers are accurate enough to rely on for plugging them back on so I went looking for IDC style plugs and sockets to make it easier for myself.

Long story, but to the point. I found IDC box things here on Thingiverse that could be popped over the pins to make male headers into box headers and similar IDC style frames that could be put around Dupont terminals on jumpers to make matching plugs. And best of all, no 6 week wait for the slow boat to bring them to me :-)

So, it you need a 'wrapper' for an Arduino Mega 2560 embedded board bristling with pins you could have a go with this, which snaps around my 'down' soldered board and leaves the USB socket uncovered. I haven't printed the version with the hole for the reset button, I can reach in the USB hole with a spudger and poke the button so its not essential for my current project. https://www.tinkercad.com/things/hP2VRmHu4Q0

When I get round to making the connection cables I'll be using these rainbow cables with female DuPont terminals already crimped (and if the photos are to believed, no plastic shells to remove first): https://www.aliexpress.com/item/32997167875.html

I'll be putting the crimped terminal ends into 2 row Dupont header casings and the casings will be finished off with the IDC locator lugs to make plugging them in wrong a real challenge (I am however the definition of the better idiot, I often break things in new and unimaginable ways). Here are some typical Dupont header shells https://www.aliexpress.com/item/32723695617.html - I already have a set complete with terminals that I will be pillaging for the shells.

I have tweaked the OpenSCAD file for the IDC plug shells as the locator lug was a little too loose a fit for me. The entire model has been made by creating three IDC Box STL files from OpenSCAD and then editing them in Tinkercad to meld them together into one lump. Several iterations of the top were needed to get it to the current point where there is a slight fore/aft mismatch between the top and bottom shells, the fit left/right is spot on for my board.

To solder the pins I use a small stack of stripboard/Veroboard to keep the pins in place and aligned with the PCB.

There is also this design for the Up board enclosure which was the first iteration of the design, before I considered using IDC style connectors and turning the board over. This has all pins accessible if you have slim fingers and the patience of a saint. https://www.tinkercad.com/things/9FqbacGRo3H

This is a work in progress and is a component of my bigger, extremely slow, project so is here as is, with no warranty and no liability accepted. You are hereby instructed to seek advice and appropriate adult supervision up your chain of command because my chain of command has her hands full with me. Have fun, be safe and don't hold the hot end of a soldering iron.