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).
- 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