User Manual

90
Lesson 13 Driving LEDs by 74HC595
Introduction
In this lesson, w e will learn how to use 74HC595 to make eight LEDs blink regularly.
Components
- 1 * Raspberry Pi
- 1 * Breadboard
- 1 * 74HC595
- 8 * LED
- 8 * Resistor (220Ω)
- Jumper wires
Principle
74HC595
The 74HC595 consists of an 8−bit shift register and a storage register with three−state parallel
outputs. It conv erts serial input into parallel output so that you can save I O ports of an MCU.
The 74HC595 is widely used to indicate multipath LEDs and driv e multi-bit segment displays.
"Three-state" mentioned abov e refers to the fact that you can set the output pins as either
high, low or high impedance. With data latching, the instant output will not be affected
during the shifting; with data output, you can cascade 74HC595s more easily. Compatible
with low voltage TTL circuit, 74HC595 can transform serial input of 8-bit data into parallel
output of 8-bit data. So it is often used to extend GPI O for embedded system and driv e low
power devices.
Pins of 74HC595 and their functions:
Q0-Q7: 8-bit parallel data output pins, able to control 8 LEDs or 8 pins of 7-segment display
directly.
Q7’: Series output pin, connected to DS of another 74HC595 to connect multiple 74HC595s
in series
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