4″ 7-Segment Display Driver

I was recently given some 4″ 7-Segment displays, Kingbright SC40-19EWA & of course, I needed to find a use for them.

I only have three, so a clock isn’t possible…

4" 7-Segment Display
4″ 7-Segment Display

As these displays are common cathode, & have a ~9v forward voltage on the main segments, some driver circuity is required to run multiplexed from an Arduino.

Driver Transistors
Driver Transistors

Driver circuit built on Veroboard, PNP segment transistors on the left, cathode NPN transistors in the centre, level-shifting NPN array on the right.

Base Bias Resistor Network
Base Bias Resistor Network

Base bias resistors on the back of the board to bias the bases of the segment drive transistors correctly.

Display Rear
Display Rear

Board soldered into the pins of the displays, which have been multiplexed.

Schematic to come along with some Arduino code to run a room thermometer, with an LM35 sensor

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