Big 7-Segment LED with SPI Interfacing

The project is utilizing cheap dot LEDs to create a big LED with an interface through SPI and can be expandable for multiple digits with only three wires for receiving data from any microcontroller boards.

For receiving serial data from microcontroller boards, the circuit is using serial-in-parallel-out shift register 74HC595. In the schematic, SER stands for data input, SRCLK is shift clock, and RCLK is latch clock. On the rising edge of the shift clock, each data bit is shifted into the register. The rising edge of RCLK will clock the data to be latched at each output bit when all data bits are shifted into the 8-bit register.

Five dot LEDs connected in series comprise each segment of the Big LED, with limiting resistor tied to +12V. The output is made to be active low due to the logic high at the input of ULN2003 making the LED current sink into the chip. The driver has 7-bit for segment a, b, c, d, e, f, and g, while Q1 is for optional point display. By connecting the QH to the next digit serial input bit, multiple digits can be easily made.

Rest of the project