Dummy SD cards are often used as place holders to protect the electrical contacts and mechanical mechanism of a card socket. During the development of the x-IMU I found a very different need for dummy SD cards. The x-IMU features a magnetometer and is sold fully calibrated. However, the spring loaded mechanism in the x-IMU’s SD card socket would create different magnetic distortions dependent on whether and SD card is present or not. In would be impractical to repeatedly recalibrate the x-IMU depending on whether an SD card is inserted or not. Use of a dummy SD card would mean that the magnetic distortions of the SD card socket could remain constant when the SD card logging functionality is not required.
It was surprisingly difficult to find a supplier of dummy micro SD cards and in the end I decided to make my own. At the time, I had access to a 3D printer at the University of Bristol so I designed a card in Autodesk Inventor according to the Micro SD Card Product Specification. The cards were usable but the FDM printer process meant the cards didn’t look all that great and had intolerances that could mean they did not fit smoothly into the card socket.
I had seen some products create micro SD card connectors using an SD card-shaped PCB of the correct thickness. 0.8 mm is a common PCB thickness and equal to the maximum permissible by the product specification. An advantage of PCB cards is that the solder mask and silkscreen layers could be used to create cards of different colours and with high resolution graphics. I design a PCB version of the card using Eagle CAD and ordered some samples from pcbpanel. I was very pleased with the results, the cards fit perfectly within the sockets and look great with the high-resolution silkscreen graphics.
All dummy micro SD card resources are open-source and available on GitHub. The resource include the Autodesk Inventor part file with compiled step file (.stp) ready for 3D printing; and the Eagle CAD board file with Gerber files ready for PCB fabrication.