Prototype - Arduino Dot Matrix LED Driver with PWM Brightness control

Prototype for driving a much larger LED matrix display with an Arduino Uno. This prototype uses 7 digital outputs to drive one quarter of one 8x8 matrix. One analog input is used to measure ambient brightness. Expecting that no more digital outputs will be required to add more matrix displays as the column driver will use cascaded 74HC595. The total number of drivable columns will be dictated by the refresh rate ('loop' duration).

- 1 x 2n4401 NPN transistor driver for every column and row
- 1 x 74HC595 8-bit shift register on both columns and rows


I/O pins used:
- #5 (output) row enable (PWM to ~OE)
- #6 (output) reset (~SRCLR on all 74HC595)
- #7 (output) row data (SER)
- #8 (output) column data (SER)
- #9 (output) row shift and latch (SRCLK & RCLK)
- #10 (output) column shift and latch (SRCLK & RCLK)
- #11 (output) column strobe (~OE)

- #A0 (input) ambient brightness (using Brick Light Sensor)

Notes:

- The 74HC595 can provide 35mA per output but there is a maximum of 70mA through Vcc. Thus the chip can drive at most 3 LEDs. To drive more than 3 LEDs a 2N4401 is used to increase the output current capability. Total draw at any moment is expected to be around 160mA for 8 LEDs.

- The PWM brightness control works well. Values less than 128 appear almost full brightness with values greater than 192 becoming noticeably dimmer.

- Column strobe delay is 1ms

- In 1 second 'loop' is invoked 225 times (using 1ms delay for column strobe; with 100us delay 1218 times)

- A bigger breadboard would be useful :)

Category:

Education

Tags:

• Arduino