Big 7 segment display boards

PCBs and Python driver for Raspberry Pi.

Uses the TLC5916, a constant current, 8 bit driver, designed for daisy chaining.

Check the video of it in action on youtube

PCB

Available from £6.50 from me.

Also available at a higher price from OSH park, hopefully will find a way to make them cheaper soon!

Python Example

import driver
driver.update("0.35") #requires 3 panels

Electronics

Important Please read and understand the power supply pins below before connecting your board to a controller.

Pins

1. Ground (0v).
2. Ground (0v).
3. +5v - The supply for the driver chip. This can be from 3.3v to 5v. It should be the same level as the logic levels of your controller. So for a Raspberry Pi which operates at 3.3v it should be connected to 3.3v.
4. +12v - The supply for the LEDs. Maximum 20V. Current is set with R1 (see notes below)
5. SDI/SDO - Serial Data In on the left of the board and Out on the right of the board (for chaining)
6. CLK - Clock. Next bit gets shifted when clock goes high.
7. LE - Latch Enable - the shift register is latched to the output when this is transitions from high to low.
8. !OE - Not Output Enable. Pulled up to the logic supply by a 500k resistor in the chip. Pull low to turn on the LEDs. Useful for PWM control of brightness.

LED arrangement

• A is bit 0 (gets clocked in first)
• G is bit 6
• Decimal point is bit 7 (gets clocked in last)

So [ 1,1,1,1,1,1,0,0 ] would be 0 with no decimal point.

The driver chip: TLC5916

Datasheet Overview

• 3.3v to 5v supply
• up to 120mA per channel
• Max LED voltage 20v

Required Components - BOM

The long digit in the following list are Farnell order numbers

• R1: 2329486, 1, RESISTOR CARBON 1K0 0.25W
• C5: 2112910, 1, CAP CER Y5V 1UF 50V RAD
• C4: 1870987, 1, CAP ALU ELEC 22UF 6.3V RAD
• C2: 1871001, 1, CAP ALU ELEC 220UF 16V RAD
• IC1: 1647814, 1, IC LED DRIVER 8CH PDIP16

And 22 10mm LEDs of your choice.

Optional Components

• 1101347, 1, SOCKET IC DIL 0.3" 16WAY
• 1097954, 1, HEADER PIN TIN 36WAY 1ROW

Notes

1. R1 sets the LED current. 1k works well at 12v supply. The lower the value the higher the current provided to the leds. See page 18 of the Datasheet
2. For cost reasons, the caps in the above list are sold in 10s only.
3. For cost reasons, the header above will do 4 boards with a few left over.

Characteristics

• with LEDs from oomlout and a 1k current resistor, average current while counting is 120mA, all segments on is 200mA.
• current sourced from !OE is 22uA.
• current drawn by 5v line (logic supply) is 10mA.

License

This hardware is licensed under the CERN open hardware license 1.2, which also included in this repository.