I was having a look at the various Panelolu designs.

More specifically at how to wire one up at the Think3dPrint3d website and decided that I needed to have a go at simplifying the wiring for use with an I2C connected LCD.

I am not using an SDSL per se, but an off the shelf Micro SD card reader that is a fraction of the cost (£5.84 vs £13.20 inc P&P)

This could potentially be done even cheaper with a standard SD card reader that can be had for about £1.14 from Ebay

If I believe I can use just 12 pins for all of the panel connectivity. If I use a couple of Dupont 2×3 connectors, then the other pins will still be available for any other uses that may come along, as they can stack side by side.
The great thing about Dupont connectors is that they are easy to change pinouts – just lift the flap that holds the pin in place, pull out the pin and move it to another slot. If you have any cables with single ends, 1×2, 1×4, 1×6 ends, you can easily change it to a different configuration if you have the appropriate connector or simply want to change the arrangement of pins from one end to the other to quickly make a custom cable.
Typical prices for Dupont pins and connectors – all prices from Ebay
100 x female pins £1.90
100 x male pins £2.25
100 x 1×2 pin connectors £1.63
100 x 1×3 pin connectors £1.63
100 x 1×4 pin connectors £2.25
100 x 1×6 pin connectors £2.25
100 x 2×3 pin connectors £2.32
40 x 1 pin female – 1 pin female wires £1.21
I use a ratchet crimper with replaceable jaws, but you can just as easily use a pair of needle nose pliers instead.
Here is the Schematic I mocked up, you will see that the PCF8574P chip handles all of the connectivity to the LCD.
I intend to use 90 degree header pins on the LCD panel and some 1×6 Dupont connectors, connection to the Micro SD board is again 90 degree header pins, a 1×6 Dupont and a 1 pin Dupont or 1×3 pin and 1×4 pin (as I need 7 pins) – total cost of connectors (3 x 1×6 connector, 1 x 1×1 connector, 2 x 2×3 connector, 30 x male pins) is about £0.80, with another £0.08 for 90 degree header pins.
Encoder – £6.19 for 10, Pots – £1.41 for 10, switch – £0.08, 2004 LCD – £4.24 and some perfboard.
If you can make do with a 1602 LCD, these can be had for £1.34.
So total parts cost for I2C Panel about £2.60 (includes cost of PCF8574P) , then add either Micro SD or standard SD, 2004 or 1602 LCD, and price varies from about £5.00 (standard SD and 1602) to £12.50 (micro SD and 2004) all in.
OK, the STL file for the panel may also need a little tweaking for my internals, but overall should be pretty simple to do.

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