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How to Make a Memory Card Reader

Author Cadence PCB Solutions

Key Takeaways

  • Memory cards offer operating system versatility and unlimited memory capacity.

  • A standard USB interface offers the dual functionality of supplying power and an excellent data exchange rate in memory card readers.  

  • A digital card reader IC is the heart of the USB memory card reader. 

 USB Memory card reader

USB memory card readers are used to read, copy, and transfer data from memory cards to computers through a USB port

Memory cards are used for data logging and offer operating systems versatility and unlimited memory capacity. Memory card readers are essential for reading data. When a device—for example, a computer—does not have memory card slots, you may need to connect a memory card reader to transfer your files.  In this article, we will discuss how to make a memory card reader.

Memory Card Readers 

A memory card reader is a simple solution for transferring data to and from a memory card. A memory card reader can be designed for communication protocols such as SPI, I2C, etc. Usually, the memory card reader adopts the USB interface to connect it to a computer. Memory card reader pinouts are compatible with all microcontroller boards and can be used for data logging in embedded system-based projects.

If utilizing SPI communication protocol, some notable pins in a memory card reader are:

  1. Power supply (VCC) - Usually, voltage regulators are used for supplying power to a memory card reader. In the case of standard 5 V power supply systems, LDO is used for supplying 3.3 V to the memory card reader. 

  2. SDI, SDO - These are the signals shared by the connected devices.

  3. Chip select (CS) - In the case of multiple peripheral devices, one can be selected using chip select signals. 

  4. GND - This pin connects the memory card reader to the ground terminal. 

USB Memory Card Readers

Typically, USB memory card readers are used to read, copy, and transfer data from memory cards to computers through a USB port. There may be one or more slots to insert a memory card. You may have the provision to select one particular card. LED indicators are used in USB memory card readers to denote which card slot is in use.

The main parts of a USB memory card reader are:

  1. USB port - A USB port offers the standard interface between the card reader and the computer. In USB memory card readers, the power is supplied by the USB.

  2. A processor - The processor makes the memory card pins compatible with the USB interface. 

The number of data pins in a memory card and a USB port is different. The processor is used to collect the data from the data pins of the memory card, process it, and return the data to the computer through a USB port. The processor makes the number of data pins compatible with the USB port. 

How to Make a Memory Card Reader

A USB memory card reader is a printed circuit board assembly that holds a memory card slot and a USB interface. To understand how to make a memory card reader, you must understand the main parts of the memory card reader, which are:

  1. Power Supply and USB Port

Usually, power is supplied from the USB in the USB memory card reader. Even when multiple memory card slots are there, the USB can supply power. In case a supply voltage other than USB voltage is available, LDO can be utilized to convert to the required voltage. A USB interface is preferred over any other protocol due to its excellent data exchange rate. With the version of the USB interface, the data transfer rate changes. ESD protection diodes are connected for the protection of the USB interface. 

  1. Digital Card Reader IC With Internal ROM

The digital card reader IC is the heart of the USB memory card reader. The digital card reader IC enables the card reader to access memory cards of different types such as SD cards, SD HC cards, etc. ICs such as GL827L, AU9331, and 73S1217F are some examples of USB card reader chips that come with internal ROM that hold the necessary data exchange firmware. The chip processor is programmed with this firmware during the time of manufacturing. Usually, these ICs have an inbuilt crystal oscillator for cocking the memory card reader.

  1. Reader Slot

The memory card slot allows the proper insertion of the memory card. The card locking system is present in the slot and secures the memory card position.

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