Arduino connected to 74C164
Fig. 1 electrical connections to Arduino.

Arduino Controlling 74C164 Shift Register

by Lewis Loflin

  
  

This sample circuit and program demonstrate the use of a shift register with an Arduino Microcontroller. Instead of using some pre-made library, the idea here is use ones own code and learn some electronics.

For more on differing LED configurations see Using the 74HC165 Shift Register with the PICAXE Micro-Controller

This demonstration will use 8 light emitting diodes (LEDs) to count in binary from 0 to 255. This will require eight bits or one byte. How this count is displayed depends on how the LEDs are connected and how the bits are shifted into the shift register.

connections to the 74HC164
Fig. 2 internal block diagram of the 74HC164.

Fig. 2 above shows a typical internal block diagram of a eight-bit shift register. In the case of the 74HC164 we have eight clocked "D" type flip-flops with common clock line (CP) and common reset line (MR NOT) that will set outputs Q0 - Q7 to all LOW or binary 0. Note in the electrical sense a HIGH or binary 1 will output (source) +5-volts while a binary 0 will switch (sink) the pin to ground.

The 74HC164 8-Bit Serial-In - Parallel-Out Serial Shift Register has three inputs:

  1. Input A-B (pins 1, 2) is for data bit to be shifted in. They can be tied together or the one not used ties to +Vcc.
  2. CP or clock pin 8 data is shifted into the 8-bit register during the positive going transition of clock pulse. That is, whatever the state of input A-B will be shift one-bit right during each clock cycle and will continue to be shifted right during each consecutive pulse.
  3. Clear (pin 9) is independent of the clock and when taken LOW (0 volts), Q0 - Q7 will all go LOW (ground) on the corresponding output pin. This pin must be initialized/held HIGH for the register to operate.

Arduino code for this project: arduino3a.txt

LEDs connected common cathode.
Common cathode configuration.

LEDs connected common cathode.

Connected to 7-segment Display

This program assumes a seven segment display with a bit pattern:

Q7 segment a
Q6 segment b
Q5 segment c
Q4 segment d
Q3 segment e
Q2 segment f
Q1 segment g
Q0 segment dp

Arduino code for this project: arduino3a.txt




 


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