UTSOURCEDIY Electronic Project: Expanding Microcontroller Inputs with the MM74HC165M Shift Register
In many electronics projects, especially those involving microcontrollers, you may find yourself running out of input pins. Whether you’re building a complex control panel or a sensor array, having more inputs can be crucial. The MM74HC165M shift register is a versatile solution for expanding the number of input pins on your microcontroller. In this DIY project, we’ll explore how to use the MM74HC165M to efficiently increase the input capacity of your project.
What is the MM74HC165M?
The MM74HC165M is an 8-bit parallel-in/serial-out shift register, which allows you to read eight parallel input signals using just a few microcontroller pins. It captures the state of its input pins simultaneously and then shifts this data out serially to your microcontroller. By daisy-chaining multiple MM74HC165M chips, you can expand the number of inputs further without using additional microcontroller pins.
Components Required
To build this input-expansion circuit, you’ll need the following components:
MM74HC165M Shift Register: The core component for expanding inputs.
Microcontroller (e.g., Arduino): To read the data from the shift register.
Resistors (10kΩ): For pull-up or pull-down purposes on input pins.
Capacitors (100nF): For power supply decoupling.
Push Buttons or Switches: To test the input expansion.
Breadboard or PCB: For assembling the circuit.
Wires and Connectors: For connections.
Power Supply: 5V DC for the microcontroller and shift register.
Soldering Kit: For assembling the components on the board.
Circuit Design
Connecting the Shift Register: The MM74HC165M has eight parallel input pins (labeled D0 to D7) that capture the state of connected switches or sensors. These inputs are then read sequentially by the microcontroller through a serial connection.
Control Pins: The shift register has several important control pins:
oCLK: Clock input that triggers the data shift.
oSH/LD: Shift/Load pin that switches between loading the input states into the register and shifting the data out.
oQH: The serial data output pin, which sends the data to the microcontroller.
oCLK INH: Clock inhibit, which can be used to control when the clock is active.
These pins are connected to corresponding digital pins on the microcontroller to control the operation of the shift register.
Input Configuration: The input pins (D0 to D7) are connected to switches or other input devices. Pull-up or pull-down resistors are used to ensure that the inputs are at a known state (high or low) when the switches are open.
Daisy-Chaining: If you need more than eight inputs, you can daisy-chain multiple MM74HC165M shift registers. The serial output (QH) of the first shift register is connected to the serial input of the next, allowing the microcontroller to read a continuous stream of data from multiple registers.
Assembly and Testing
Assemble the circuit by placing the MM74HC165M on a breadboard or PCB. Connect the input devices (e.g., push buttons) to the parallel inputs of the shift register, and connect the control pins (CLK, SH/LD, QH) to the appropriate pins on the microcontroller.
Write a simple program for the microcontroller to read the serial data from the shift register. The program should trigger the SH/LD pin to load the input states and then pulse the CLK pin to shift the data out, reading each bit sequentially.
Power on the circuit and test the input devices. The microcontroller should correctly read the state of each input, even though it uses only a few of its pins. If multiple shift registers are daisy-chained, the microcontroller will read all inputs in a single operation.
Applications
This input-expansion technique is ideal for applications such as:
Control Panels: Where multiple switches or buttons need to be monitored.
Sensor Arrays: In projects that require reading data from numerous sensors.
Keypads: For creating custom keypads with many buttons.
Conclusion
Using the MM74HC165M shift register to expand the input capabilities of your microcontroller is a practical and efficient solution for many projects. It allows you to manage more inputs without needing additional microcontroller pins, making it an essential tool for complex electronics designs. Whether you’re building a control system, a large sensor array, or any project requiring numerous inputs, this shift register offers a straightforward way to scale up your project’s capabilities.
From Utsource：www.utsource.net
