LCD/SD card backpack

LCD/SD card backpack

I still had some parts in my breadboards from a prior project and was hesitant to take apart the SD card and LCD display portion. These two things are very useful items to have easy access to and both can be complex to setup.

Old breadboard setup

I looked at buying a “proper” SD card breakout that includes the voltage conversion, but I already had the simple breakout PCB and level conversion IC so I thought I should just make one. I also looked at the i2c/SPI character LCD backpack from Adafruit but I had just bought a 20×4 RGB LCD and that board will not support driving the green and blue LEDs. This lead me to design my own board that combines the two with the SD card under the screen. I decided that I wanted the SPI for the LCD as well as access to the original LCD pins.

LCD/SD Schematic

After I did some initial layout I decided it would be fun to use some wire wrap parts that I got from my grandfather, a retired electrical engineer. This allowed me to use my current SD breakout by just wire wrapping to the pin header.

Electric wire wrap tool

This is only the second time I have ever used wire wrap, the first time was a simple ribbon-DIP adapter. As such I did some research into proper wire wrap technique and found a nice high level manual from NASA and a MIL spec, MIL-STD-1130, with excellent detail.

Bottom view

I initially forgot to put a jumper to select either the SPI or the normal LCD pins. I had to add a jumper and pull-up resistor at the end (it is not shown on the schematic here). The final features are:
SD card:

  • 3.3v supply and level conversion
  • Access to write protect and card detect pins

LCD Screen:

  • SPI interface OR Standard LCD pins (RS, E, DB4, DB5, DB6, DB7) (jumper selectable)
  • SPI controlled backlight OR RGB backlight support (jumper selectable)

The last thing to do is 3D print an enclosure to protect the wire wrap. Once I get my printers working again I will print one and post an update.

More photos on flickr
Continue reading