Driving a 4-Digit 7-Segment display with only 3 pins, using two 74HC595 shift registers and some n-channel FETs
This circuit is a variation of the DoubleShift experiment that demonstrated how to use two 74HC595 shift registers and some NPN BJTs to drive a 4-digit 7-segment display with only 3 Arduino GPIO pins.
The only difference here is that the S9013 NPN BJTs are replaced with 2N7000 n-channel FETs.
When fully on (e.g. displaying 8888), it appears the display and associated components on the breadboard are drawing an average of about 2.47mA (compared to 2.87mA with BJTs).
Credits and references
- 74HC595 Datasheet
- 2N7000 Datasheet
- KW4-561 Datasheet - not matching the part I have, but a pretty stanrd example
- a good How to.. question at EE.SE
- 2 Shift Registers 74HC595 Cascading with LED Display