Espruino Parallel to Serial Shifting-In with a CD4021BE

Overview

This module interfaces with the CD4021BE (also know as HEF4021B), a cheap 8-bit static shift register. They are used in the parallel to serial shifting-in. They also have capability to work in cascading mode without requirement of more Espruino pins to make that work. Support is included in the CD4021BE (About Modules) module.

It's a nice alternative to expand the IN possibilities of your Espruino project.

Key Specifications:

Wiring (Example for Espruino Original)

*You can use any other SPI/GPIO available in your Espruino Board. See in board pin references

Usage

call require("CD4021BE").connect(, ) to get a CD4021BE object. Take use of this object calling read() method. The result will be a array with current status for each port of CD4021BE.

For example:

  SPI2.setup({sck: B13, miso: B14, mosi: B15});
  var shift_in = require("CD4021BE").connect(SPI2, C6);
  console.log(shift_in.read()); // [ 0, 0, 0, 0, 0, 1, 0, 0 ] - This means that only port 6 is in high level

You can also read lots of CD4021BE in cascading mode, just by passing how many you have as the last connect() param and than call the readAll() method passing a callback function as a param to get the values. The result will be a array of arrays with current status for each ports of each CD4021BE in cascading order.

For example:

    SPI2.setup({sck: B13, miso: B14, mosi: B15});
    var shift_in = require("CD4021BE").connect(SPI2, C6, 3);
    shift_in.readAll(function(values) {
        console.log(values); // [ [ 0, 0, 0, 0, 0, 0, 0, 1 ], [ 0, 0, 0, 0, 0, 1, 0, 0 ], [ 0, 0, 1, 0, 1, 0, 0, 0 ] ] - The status of three cascading CD4021BE
    });

Buying

CD4021BE IC is extremely cheap. This IC can be purchased from many places:

• eBay
• AliExpress

Reference

• Technical Data