Thursday, November 20, 2014

Shift register using 74HC595

I used two 74HC595 chips hooked to the Serial Peripheral Interface Bus of an Arduino.   This bus will runs at 4MHz so the updates to the LEDs were very snappy.

A single chip can only control 8 LED's.  In order to control another 8 chips you have to connect a second chip to the first chip in series.   

 Shift Register Example
 for 74HC595 shift register

 This sketch turns turns your arduino into a cylon.

 * 74HC595 shift register attached to hardware SPI
 Arduino               74HC959
  pin# name            pin#  name
  10 SS        --->    12 RCK
  11 MOSI      --->    14 SI
  13 SCK       --->    11 SCK
 * LEDs attached to each of the outputs of the shift register

 Created 02 Oct 2014
 by James M. Rogers

 Based on work of others found in following locations:,149470.0.html


#include <SPI.h>

int pinSS=10; //latch

int d=40;

void setup() {

//#define d 40
void loop() {

    int i;
    for (i=0 ; i<16 ; i++) {
      registerWrite(i, HIGH);
       delay (d);
    for (i=15 ; i>=0 ; i--) {
      registerWrite(i, HIGH);
       delay (d);

  if (d>10)
    if (d==0)

// This method sends bits to the shift register:
void registerWrite(int whichPin, int whichState) {
// the bits you want to send
  byte lowbitsToSend = 0;
  byte highbitsToSend = 0;

  if (whichPin <8) {
    // turn on the next highest bit in bitsToSend:
    bitWrite(lowbitsToSend, whichPin, whichState);
  } else {
    bitWrite(highbitsToSend, whichPin-8, whichState);


Picked up a Radio Shack 46 Range Multimeter (part #: 2200029) on clearance the other day

It seems like a decent multimeter, but it only came with windows software for the usb port.  I made sure that the multimeter worked through the usb port to a windows machine, and it did.  This windows software is not scriptable, and it is obviously written over a decade ago without any software updates.  The worst part is that this software limited me to only running the meter hooked to a windows desktop machine.

If I could find some software to work with the newer usb version of the meter on Linux, that would be best, but I was only able to find very old versions of the software that could not decode the format. So I just began to dump the format out and work out the coding myself.

A friend of mine sent me a link to some older command line software that worked with a previous RS-232 version of the meter, and the decoding routines worked with the usb version I have.  Unfortunately this version of the software would not release the tty after it was ran once and then the program forced to quit.  But I found even older software that couldn't decode the format, but properly handled connecting to the tty so it would disconnect on exit.

At that point I added a date and time stamp and called it done, this version is here:

Example of the log output

But I wasn't done yet.  There are times when I need to take a reading, but can't see the LCD screen from where I am positioned. Also it might be nice if a blind person could use this meter to read out meter settings under Linux for low voltage things like Arduino or building a little circuit. So I decided to make the meter talk.  This version is here:

I am thinking of making a graphical display of the meter, and graphical view of the logging to make things easier for non Unix people who are running Linux.

I was able to do this easily because I found this example code on how to use espeak library from a post on stackoverflow.  I have a copy of the example code that I cleaned up a little bit here: