Digital PDP-8/I – continued – Emulating in SIMH

As mentioned in a previous post, this family of devices was used in many of the in-house test systems for the central incoming test group also located in our building as well as some of the newer PDP-11 series devices.

It has a very small instruction set and a word size of 12 bits. First devices where delivered with 4K words that could be extended to 32K words using an extension board in the integrated circuit models.

These devices supported ASR33 ‘typewriters’ that also supported paper tape for entering and saving code. There were also TU56 tape (184K) drives which essentially worked more like random access disk drives than what we traditionally think of as tape drives. There was also disturbingly large disk drives with seriously small storage space (less than 3Mb). Later in the series, there was also an 8″ floppy called the RX01, which I personally encountered on the WT78 Word Processor while doing my college homework (with permission… after hours at the office). A slightly larger storage capacity 8″ RX02 arrived the same year.

Configuring a PDP-8 in SIMH

The environment I’m using is based on Oscar Vermeulen’s Pidp8 (a Raspberry Pi Zero with with switches and led’s emulating a PDP-8 front panel). Oscar assembled a custom release of SIMH 4.0 including a GPIO handler to drive the LEDS and read the front panel switches for a full retro-experience.

There is a website that stores many PDP-8 device images that can be used with the SIMH/PDP8 emulator. They are found here, pdp8 online

Examples:

$wget http://www.pdp8online.com/ftp/images/misc_floppy/os8_v3d_bin_1.rx01
$wget http://www.pdp8online.com/ftp/images/misc_floppy/os8_v3d_bin_2.rx01

Using the PiDP-8/I front panel

If it’s not clear, when the top of the switches on the panel are pressed IN, the switch is in a “0” state, and when the bottom of the switch is pressed in it represents a “1” state.

PiDP-8/I Simulator

I have a brief but ancient history with the PDP-8 from Digital Equipment Corporation. I started working for DEC in the winter of 1977/78, just after my senior year in high school. I was in college studying radio/television production. When a film crew arrived one day to make a training video for the company, I asked if I could intern on the project. I’d worked there a while by then and had a good relationship with my boss, so I got a green light to do it.

The training video project was for a dedicated bed-of-nails tester for the new PDP-11/23 board that was about to go from prototype assembly to full production in Puerto Rico. The facility that I worked at performed central incoming chip testing as well as the prototype assembly process for the PDP-11/23. All of the test equipment was driven by DEC PDP computers, which was pretty impressive.

The test machine we were making a video for had a massive amount of input/output pins that were controlled by the PDP-8. It had a paper tape reader, an RK08, a console terminal interface and an expansion chassis that led to the 3rd-party I/O pin controllers and timing hardware. The bed of nails fixture was built specifically for the PDP-11/23 and used sharp spring loaded pogo pins for connectivity to all the “special places” to be probed on the underside of the board.

In the training video, I showed how to perform the boot process, that involved loading a series of commands into the front panel in octal. These steps told the machine how to read the paper tape. The next step was to run what the paper tape loaded (The tape drive), which was the program that knew how to spin up and use the RK08 disk and make the serial terminal work. From there, the text application could be executed from the operator terminal.

So where is all this leading?

I just purchased a kit from Oskar Vermeulen called PiDP-8, a PDP-8/I simulation with real front panel switches and blinken lights. Yes, Blinken does mean “to flash” in German. The kit is based on a Raspberry Pi and uses the SIMH computer simulation program.

pidp8PDP

His website is at Obsolescence Guaranteed

I’m still waiting for the kit to arrive… but I have the PI running.

Screenshot 2016-04-26 20.11.40

Arduino IDE on Ubuntu – easy way

Here is the simplest way to get the latest Arduino IDE installed on a freshly installed  Linux Ubuntu distribution.  The version of Arduino that is in the default repository is now a few years old, and in fact, the version you will get is officially “…no longer supported by the development team.”

But, there is an upside to this.  By performing the following command you get a complete guided installation that will install all the compiler dependencies and do nice things such as making your account part of the dialout group, which is needed to access the serial port.


sudo apt-get install arduino

So, with this accomplished lets download the latest version from
Arduino Download Page and make sure you choose the linux version that matches your system (32 bit or 64 bit).

Version

NOTE: The latest version is subject to change, so replace references to “1.6.8” with what ever the current downloadable version is.

The installation kit will normally end up in your “Downloads folder” so lets open a terminal window and go there to unpack it.


$ cd Downloads/
$ ls
arduino-1.6.8-linux64.tar.xz
$ tar -xvf arduino-1.6.8-linux64.tar.xz

This will place the files in a new folder named: arduino-1.6.8

Now, we can place it anywhere, but a nice place to put it is in the /opt top level folder. This can be accomplished with the following step:


sudo mv arduino-1.6.8 /opt

Now, move your /opt folder by typing:


cd /opt/arduino-1.6.8

and then issuing the following command to make this installation of arduino “go live”


chmod +x install.sh
./install.sh

You should now have an Arduino icon on your desktop that will open the latest “supported” version of the IDE.

An approach to writing Arduino code

Code Review

Let’s do an example of code development.

Let’s say that we are reading analog values for ranges and want to make decisions based on ranges to set ranges of values. We start with the following snippet. The `if` statements quickly become wordy and program flow maybe starts to become unclear.  So lets look at some ways to unravel this with a subroutine.


reading = analogRead(1);

int state = 0;

if (reading > 0 && reading < 500){ 
state = 1; 
} 

if( reading > 499 && reading < 700) { 
state = 2; 
} 

if ( reading > 699  && reading < 1025) {
 state = 3;
}

You could just write a small procedure  to simplify this comparison test series…


bool inRange(int x, int y, int z){

 if (x => y && x <= z) {
      return true;
     } else {
      return false;
     }
}

and then call it with much easier to read process requests… like the following code.


//file inrange.ino

// State 1: Connect analog pin to gnd
// State 2: Connect analog pin to 3.3V
// State 3: connect analog pin to 5V

int reading;
int state = 0;

void setup() {
  // put your setup code here, to run once:
 Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
reading =  analogRead(1);

  if(inRange(reading,0,500))
     state = 1;
  
    if(inRange(reading,500,700))
       state = 2;
    
      if(inRange(reading,700,1024))
         state = 3;
      
    Serial.print("Reading ");
    Serial.println(reading);
    Serial.print("state: ");
    Serial.println(state);
    delay(1000);
}

//-------------------------------------------------
// Notice the use of non-informative variable names
// we should fix this.

int inRange(int x, int y, int z){
   bool val;
   if (x >= y && x <= z) {
      val =  true;
    } else {
      val = false;
    }

    return(val);
  }


See? You really get some better logic flow this way.

New lets go a step further… using space saving `const` or constants.


// File: inrange1.ino

// State 1: Connect analog pin to gnd
// State 2: Connect analog pin to 3.3V
// State 3: connect analog pin to 5V

//=====[ CONSTANTS ]============================================================
//Still a bit wordy here...
const int RED = 0;
const int GREEN = 1;
const int BLUE = 2;

//=====[ PINS ]=================================================================
int anPin = 1;


//=====[ VARIABLES ]============================================================
int reading;
int state = 0;



void setup() {
  Serial.begin(9600);
  // Wait for USB on Leonardo and similar devices
  while (!Serial) {
  }

}

void loop() {
  reading =  analogRead(anPin);
  
  // debugging code...
  Serial.print("Reading ");
  Serial.println(reading);



  if (inRange(reading, 0, 499)) 
    state = RED; 
    
  if (inRange(reading, 500, 699)) 
    state = GREEN;
  
  if (inRange(reading, 700, 1024)) 
    state = BLUE;
    
  ColorState();

  delay(1000);
}

//==============================================================================

int inRange(int passVal, int minVal, int maxVal) {

  if (passVal >= minVal && passVal <= maxVal) {
    return true;
  } else {
    return false;
  }
}
//==============================================================================

void ColorState() {
  Serial.print("State: ");

  switch (state) {
    case RED:
      Serial.println("Red");
      break;
    case GREEN:
      Serial.println("Green");
      break;
    case BLUE:
      Serial.println("Blue");
      break;
    default:
      break;

  }
}

Now we start to see how to break out sections of code into useful re-usable subroutines. So lets take this one step further and refine it into a final version using the `enum` command. Notice how the code becomes even a tiny bit simpler.


// File: inrange3.ino

// State 1: Connect analog pin to gnd
// State 2: Connect analog pin to 3.3V
// State 3: connect analog pin to 5V


enum States {
  RED,
  GREEN,
  BLUE
};

States state = RED;  // use the enumeration and initialize to RED

//=====[ PINS ]=================================================================
int anPin = 1;


//=====[ VARIABLES ]============================================================
int reading;

void setup() {
  Serial.begin(9600);
  // Wait for USB on Leonardo and similar devices
  while (!Serial) {
  }

}

void loop() {
  reading =  analogRead(anPin);

  if (inRange(reading, 0, 499))
    state = RED;

  if (inRange(reading, 500, 699))
    state = GREEN;

  if (inRange(reading, 700, 1024))
    state = BLUE;

  ColorState(state);

  delay(1000);
}

//==============================================================================

int inRange(int passVal, int minVal, int maxVal) {

  if (passVal >= minVal && passVal <= maxVal) {
    return true;
  } else {
    return false;
  }
}

//==============================================================================

void ColorState(int range) {
  Serial.print("Condition: ");

  switch (range) {
    case RED:
      Serial.println(" Red");
      break;
    case GREEN:
      Serial.println(" Green");
      break;
    case BLUE:
      Serial.println(" Blue");
      break;
    default:
      break;

  }
}


So while this is not the best code, it definitely accomplishes the simplification goal in the main process loop.

Food for thought.

Raspberry Pi – Node.js – Mongodb recipe

Node.js with Mongodb build

Post install cleanup


sudo apt-get update
sudo apt-get remove --purge wolfram-engine
sudo apt-get remove --purge minecraft-pi python-minecraftpi
sudo apt-get remove --purge penguinspuzzle
sudo apt-get remove --purge scratch nuscratch sonic-pi

Remote Access with VNC

sudo apt-get install tightvncserver

Setup password…

vncserver -geometry 1024x728 -depth 24 -dpi 120

Kill the server in preparation for boot automation…

vncserver -kill :1

Setup the autostart init.d based file in `/etc/init.d`

sudo nano /etc/init.d/vncserver

File contents:

#!/bin/sh
### BEGIN INIT INFO
# Provides: VNC
# Required-Start: $local_fs
# Required-Stop:
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: Start or stop the VNC server
### END INIT INFO

PATH=/sbin:/usr/sbin:/bin:/usr/bin

eval cd ~pi

case “$1” in
start)
su pi -c “/usr/bin/vncserver :1 -geometry 1024×728 -depth 24”
echo “Started VNC server.”
;;
stop)
su pi -c “/usr/bin/vncserver -kill :1”
echo “Stopped VNC server.”
;;
*)
echo “Usage: vncserver [start|stop]” >&2
exit 3
;;
esac

exit 0

The following commands will set up the new file so it will operate correctly…

sudo chown root:root /etc/init.d/vncserver
sudo chmod 755 /etc/init.d/vncserver
sudo update-rc.d vncserver defaults

Now we need to add cut/paste support…

sudo apt-get install autocutsel

and add it to the VNC startup file in the PI user account…

sudo nano .vnc/xstartup

so it looks like this:


#!/bin/sh
autocutsel -s CLIPBOARD -fork
autocutsel -s PRIMARY -fork
xrdb $HOME/.Xresources
xsetroot -solid grey

#x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
#x-window-manager &
# Fix to make GNOME work
export XKL_XMODMAP_DISABLE=1
/etc/X11/Xsession

Installing Nodejs dependencies:

build-essential and git

sudo apt-get install build-essential git

Node.js

wget http://node-arm.herokuapp.com/node_latest_armhf.deb sudo dpkg -i node_latest_armhf.deb

MongoDB

git clone https://github.com/svvitale/mongo4pi.git cd mongo4pi sudo ./install.sh

Arduino rant

Programming Framework

This post is about coding as much for yourself as for others. While it’s really easy to write pages of code with only a few comments, in the long run, writing well structured and clearly legible code helps a lot when you return to it months later and are forced to ask yourself “What was I thinking?”

Programmers Lament: ‘I think I wrote this section of code late at night after I had a few beers with friends. I think I need to go out and have a few beers to understand why I wrote it like this.’

I try to write all my code as if I was about to post it to public blog and that the reader will have only rudimentary knowledge of what my goal is. This means that I will need to explain myself clearly. This will impact the kind of comments I write and will remind me that resorting to cute code tricks and obfuscation (even accidental) is a bad idea.

I will admit that I am not a professional programmer, but I play one on IRC. Joking aside, I am not even a trained programmer unless you count reading books on programming. My advice here comes from concepts I have learned through years of reading other peoples code. I have found that what I call the “good” code is written by someone who is well organized writes decent comments and is reasonably methodical in how they break down a problem. Some of my own ideas start as inspiration from these organized and creative programmers whose shoulders I stand on. I will show you a programming template technique I learned from Jon McPhalen. See what I did there? Programming rule #1 should be, “Always include attribution and give appropriate credit for your borrowed ideas”.

While there are some decent books on programming style, it’s not the main focus here. This is about remembering that you could have a future audience that reads your code, so writing efficiently, being consistent and adopting good conventions is paramount.

Using a template for organized code

The Arduino environment already enforces a certain method of coding on us. It requires us to write using the core C++ language and that we employ two sections of functionality in our code. So the base minimum code is the well understood:

void Setup() {

} 

void Loop() {

}

While it is nice that the Arduino developers have saved us a lot of trouble but making “getting started” so easy, it doesn’t much help when you come back later to revise your code later and are clueless because you thought, “I’ll make it pretty later” and you never do. I have adopted a starting point for code that includes some more information than just the bare minimum required. The goal here is to start with a template that is nicely sectioned out so you have a road map for moving forward.

 

Here is an example of a template as a starting point:

//==============================================================================
// TTTTT EEEEE M   M PPPP  L      AAA  TTTTT EEEEE        III  N   N OOOOO 
//   T   E     MM MM P   P L     A   A   T   E             I   NN  N O   O 
//   T   EEEE  M M M PPPP  L     AAAAA   T   EEEE          I   N N N O   O 
//   T   E     M M M P     L     A   A   T   E      ..     I   N  NN O   O 
//   T   EEEEE M   M P     LLLLL A   A   T   EEEEE  ..    III  N   N OOOOO 
//==============================================================================
//==============================================================================
// Program: template.ino
// Author: Pete Willard
// Version: 1.0
// Target: Uno
// Date: 2015/04/02
// Time: 06:41:02
// Notes:
//
// ----------------------------------------------------------------------------
// 'THE BEER-WARE LICENSE':
// petewillard@gmail.com: As long As you retain this notice you
// can do whatever you want With this stuff. If we meet some day, And you think
// this stuff is worth it, you can buy me a beer in return. Pete Willard
// ----------------------------------------------------------------------------
//
// Reference:
//==============================================================================

//=====[ INCLUDE ]==============================================================

//=====[ CONSTANTS ]============================================================
#define DEBUG 1 // 0 = debugging disabled, 1 = enabled

//=====[ PINS ]=================================================================
int onboardLed = 13;

//=====[ SETUP ]================================================================
// Runs only one time at startup
void Setup() {
pinMode(onboardLed,OUTPUT);

}

//=====[ MAIN PROCESS LOOP ]====================================================
void Loop() {

}

//=====[ SUBROUTINES ]==========================================================
void printBreak() {
Serial.println("=============================");
}

 

I actually went so far as to write a small program that uses a fill in form to create this template format on demand. It even creates that retro-style banner with the file name spelled out on top.

A quick review shows that the template has defined a sample constant that you can use while debugging code. Changing this constant between 0 and 1 will enable you to write some conditional code that will print or stop printing debugging data with just 1 edit.

It also contains an example of using meaningful names. Using the variable assignment such as ‘onboardLed’ for pin 13 helps to make the code more readable.

Variable names don’t have to be short and are much better when multiple words are compounded into a meaningful descriptive names. For enhanced readability, try to avoid using using ALLCAPS and avoid variables with leading underscores. Try to adopt the much more accepted “camelBack” notation. This notation starts with lowercase and is the practice of writing compound words or phrases such that each following word or abbreviation begins with a capital letter*. Inserting underscores inside variable names makes the camelBack method redundant so just pick either one and stick with it.

* The case where the leading letter is lowercase but all subsequent words are capitalized is also called the Microsoft style.

Modular thinking

To me, when it comes to reading other peoples code, there is nothing more disturbing than reading page full of if conditional statements that include redundancies and a clear sign of poor planning. If I need to keep track of more than a few conditions while reading code I find that the logic of what “was intended” to be easily lost.

My approach to solving this has always been to create function blocks of code and keep the main section, in our case the Loop(), as clear and readable as possible. In C, this is called creating a “function” and it is sometimes referred to as a procedure or subroutine. I personally use all three terms interchangeably.

In most cases, you will write a procedure that accepts an argument and returns a result but this is not a requirement. For example, you can have a subroutine that just performs a task that makes the rest of your code look cleaner. Like this:

void printBreak() {
  Serial.println("=============================");
} 

So in your main code, all you need to type is:

printBreak();

In one of my programs, I have a Loop() section that basically contains 3 steps:

sampleSensors();	// collect all external sensor variable data into a “struct” variable</span>
printResults();	// send the results in 1 CSV formatted line</span>
cycleCheck();		// is it time to get updates from sensors?</span>

The functionality of the loop section remains readable and it is not bogged down with actual logic decisions. The logic and action steps are reserved for the procedures themselves and the procedures call other procedures to keep things organized. Breaking up tasks will actually help make your procedures more useful and in a lot of cases… re-usable.

I finally got around to documenting how I wired my MendelMax 3D printer

Mendelmax wiring

Mendelmax wiring

I recently added a 24V Kapton heatbed and new Y rail system to replace the finicky dual rod system. The upgrade required me to remove the existing 12V power supply and replace it with a 24V 200W supply. Since only the new heater in the bed requires the 12V I also installed an adjustable Stepdown DC/DC regulator (A 12A unit for sale on Amazon for about #$12 under the name DROK). The unit does get slightly warn during use, so I added a small fan for the smaller regulator that supplies 12V for all the motors, the controller boards and the fans.

The power for the Arduino mega is controlled via a switch from a 12V distribution panel I purchased at Autozone designed to allow power control for up to 6 unique devices. So the unit can still run standalone if needed. I removed the Diode on the Ramps 1.4 board that supplies power to the Arduino since there are those times when you just want to kill power to the arduino board.

The on board Polyfuses were removed and replaced by a piece of hookup wire.  The fuses for the power source are now panel mounted using standard 3AG fuse holders.

Note: My USB cable that comes from the PC already has a switched power option.

 

On a side note: Working with Brian at Ultibots regarding my Y axis upgrade was a superbly positive experience.  Ultibots is now my first choice for parts. 

So… I ordered a Spark Core…

… and these things are really neat.

Ok, so what is a Spark Core?   Wait…  lets start with the fact that this was a Kickstarter project that succeeded and is now a full fledged product that sadly I did not know about until afterwards.  I’d have been there supporting this Kickstarter if I had known about it. I tried to support a different but *very* similar Kickstarter project (well, not tried, I did support it) and have yet to see the product that is now many many months late. Now that I have the Spark core, and I like it, I’m pretty sure I won’t care when the Flutter *finally* arrives.

spark core image

spark core

 

So, back to what a Spark Core is.  It is a small device, roughly the size of an oversize collector edition US postage stamp.  It’s designed to fit into a Solder-less breadboard for easy project development and comes in 2 flavors… one with an on-board “chip” antenna and one with a small antenna jack that allows you to install your own wifi antenna… I grabbed an antenna out of my pile of broken wifi routers.  I wasn’t sure it would work… but seems to work just fine and uses the same RF jack (imagine that?).

For more information on what a Spark Core is, go here: Spark Core Getting Started

So what am I doing with it? Well, I’m learning what it can do first… and that’s a tiny bit tricky. The documentation is written more geek than noob friendly and while I have no issue with the documentation in general, it does seem to have some gaps here and there. I suppose with time this will all get better.

For example; they did make it seem like it would do some automagic things to get it quickly “registered” in the cloud and that my phone app could talk to it right away. No such luck. My Phone app never found the device and the status LED said I was happily connected. I needed to go through a rather manual process of attaching to the device in a serial debug mode to capture my unique ID to claim my core manually. Again, it was supposed to just work… but a quick check says I’m not the only one this happened to. (ed. I did acquire an additional spark core and the second one installed and connected and was claimed without a hiccup)

With that initial stumble out of the way… I needed to see how Arduino compatible this is so I started writing some code. As long as I stick to true Arduino’s abstract language (and not hardware dependent short cuts like you might find in some existing libraries) all is well. This device does not have an AVR MCU at it’s heart. It uses an STM32 MCU which is a much more capable device coupled with a TI CC3300 wifi in-a-box chip to create a complete arduino-like wifi device in a seriously small package.

My first project on the device after playing with examples is a simple “always correct” LED clock using the SparkFun 4 digit seven segment serial LED. It works… and displays the correct time as soon as it boots up with no need for battery backup or an RTC chip. The part number COM-11629. This is a mildly depressing LED display due to the fact that it is running on 3.3 volts and has 1000 Ohm current limiting resistors on the LED’s. (Did I mention that the Spark Core is a 3.3V device? No? oops.)

Seriously… 1000 Ohms at 3.3 volts is not the ideal value of the current limiting resistors. It should be around 47 Ohms… not 1000 Ohms. The end result is you can only really see the display in the dark.

2014-12-05 14.10.37

Anyway… the code part works… It uses built in features like wire library and time library that are already in the API. Here, see for yourself*…


//==============================================================================
//  III  2222   CCCC  CCCC L     OOOOO  CCCC K   K
//   I       2 C     C     L     O   O C     K  K
//   I    222  C     C     L     O   O C     KK
//   I   2     C     C     L     O   O C     K K
//  III  22222  CCCC  CCCC LLLLL OOOOO  CCCC K   K
//==============================================================================

//==============================================================================
// Program:      I2Cclock
// Author:       Pete Willard
// Version:      1.0
// Target:       SparkCore
// Date:         2014/12/04
// Time:         08:14:45
// Notes:

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

//
// Reference:
//  Used rather sketchy Sparkfun serial LED display "datasheet"
//  Part #  COM-11629 - Note: it's a rather dim display.
//==============================================================================
 # define bitSet(value, bit)((value) |= (1UL << (bit)))
 # define bitClear(value, bit)((value) &= ~(1UL << (bit)))

//=====[ CONSTANTS ]============================================================
// # define DEBUG 0 // 0 = debugging disabled, 1 = enabled
//This is the default address of the OpenSegment with both solder jumpers open
 # define DISPLAY_ADDRESS1 0x71

// definitions from sparkfun for bitwise led controls (decimal/colon/dot)
 # define COLON 4
 # define DOT 5

// Time Sync and Time Zone settings
const int syncInterval = 60 * 60 * 8; //sync every  4 hours

static signed char const DEFAULT_TIME_ZONE = -4;

//=====[ VARIABLES ]============================================================
long millisTimer;
int lastSync = 0;
boolean colonOn = false;
boolean ampm = true;
char bits; // used to track binary values for bitwise

//=====[ SETUP ]================================================================
void setup() {


	Spark.connect();
	 while(Spark.connected() == false) {
	     delay(100);
	 } while(Time.year() == 1970)
	  {
	     Spark.syncTime();
	     Spark.process();
	     delay(100);
	  }
	 Spark.disconnect();
	 while (Spark.connected() == true) {
	     delay(100);
	     Time.zone(DEFAULT_TIME_ZONE);
	 }
	 
	Wire.begin(); // join i2c bus as master
	Wire.beginTransmission(DISPLAY_ADDRESS1); // transmit to slave device #4
	Wire.write('v');
	Wire.write(0x7A); // Brightness control command
	Wire.write(100); // Set brightness level: 0% to 100%
	Wire.endTransmission(); // stop transmitting

}

//=====[ MAIN PROCESS LOOP ]====================================================
void loop() {
	ampm = Time.isAM();
	showTime();
	delay(1000);
	adjustTime();
}

//==============================================================================
void adjustTime() {
	if (lastSync + syncInterval < Time.now()) {
		Spark.syncTime();
		lastSync = Time.now();
	}
}

//==============================================================================


//==============================================================================
//  Must be called after a "begin.transmission()" command.
//==============================================================================
void colonFlash() {
	//Blink the colon every other second

	if (colonOn == true) {
		colonOn = false;
		bitClear(bits, COLON);

	} else {
		colonOn = true;
		bitSet(bits, COLON);

	}
	Wire.write(0x77); // control command
	Wire.write(bits); // Turns on colon
}

//==============================================================================
//  Must be called after a "begin.transmission()" command.
//==============================================================================
void setPM() {
	if (ampm == true) {
		bitClear(bits, DOT);
	} else {
		bitSet(bits, DOT);
	}

	Wire.write(0x77); // control command
	Wire.write(bits); // Turns on colon

}

//==============================================================================
void showTime() {
	char out[] = {
		0,
		0,
		0,
		0
	}; // place holder for time array

	char hour = Time.hourFormat12();
	char min = Time.minute();

	sprintf(out, "%2d%02d", hour, min); // format current time into char array
	Wire.beginTransmission(DISPLAY_ADDRESS1); // begin I2C transmit to device

	setPM();
	colonFlash();

	for (byte x = 0; x < 4; x++)
		Wire.write(out[x]); //Send a character from the array out over I2C
	Wire.endTransmission(); //Stop I2C transmission

}


So, how does Serial.readBytesUntil() work?

I’ve been toying with the idea of setting the clock on my Arduino RTC (a DS3234 dead-on real time clock) because even though it still keeps good time, it’s still impacted by daylight savings time changes and because setting the time using a boot-loader based upload can be such a hit or miss sort of thing.

So, to accomplish this in as close to real-time as possible, I started thinking about how I could send commands to the arduino from Python code on my Raspberry Pi. I opted for a COMMAND,DATA structure to simplify parsing.

The goal is to keep it simple and to use a part of the serial library that I have not used yet: “Serial.readBytesUntil()” while avoiding the requirement to include “string.h” in my code. Why? Because I need this to be part of a larger program that already stretches the limits of available RAM on my UNO. The upside of using “readBytesUntil” is that you don’t have to keep checking the input buffer and assemble an array of char… the downside of using “readBytesUntil” is that it has a default timeout of 1 second. So how useful this is in the end remains to be fully tested.

Right now, there is no bounds checking… so if the command text is larger than 10 chars and data is larger than 15, you get “unpredictable” results.

Arduino Code:

 

//==============================================================================
// Program:      SerialParse.ino
// Author:       Pete Willard
// Version:      1.0
// Target:       UNO R3, IDE 1.03 
// Date:         2013/04/08
// Time:         09:47:54
// Notes:        
//               Uses Serial I/O
// Reference:    
//==============================================================================
 
//=====[ INCLUDE ]==============================================================
//#include <stdlib.h>
 
 
//=====[ CONSTANTS ]============================================================
#define   DEBUG   1   // 0 = debugging disabled, 1 = enabled
const int bSize = 20; 
 
//=====[ PINS ]=================================================================
int Led = 13;
 
//=====[ VARIABLES ]============================================================
 
    char Buffer[bSize];  // Serial buffer
        char Command[10];    // Arbitrary Value for command size
        char Data[15];       // ditto for data size
        int ByteCount;
 
//=====[ SUBROUTINES ]==========================================================
 
void SerialParser(void) {
//
//  One command per line.  Eventually, Data may have multiple 
//   fields separated by ":"
//  Command Format: "up to 5 Letter command, up to 10 letter data<\n>"
//                  No checking.
//
//  count will  be below Zero on a timeout.
//  read up to X chars or until EOT - in this case "\n" 
 ByteCount = -1;
 ByteCount =  Serial.readBytesUntil('\n',Buffer,bSize);  
 
   if (ByteCount  > 0) {
        strcpy(Command,strtok(Buffer,","));
                  
        strcpy(Data,strtok(NULL,","));             
   }
   memset(Buffer, 0, sizeof(Buffer));   // Clear contents of Buffer
   Serial.flush();
}
 
 
//=====[ SETUP ]================================================================
void setup() {
    Serial.begin(9600);
    pinMode(Led,OUTPUT);
    if (DEBUG) {
        Serial.println("Debugging Enabled");
    }
     
}
//==============================================================================
 
//=====[ LOOP ]=================================================================
void loop() {
 
    SerialParser();
         if (ByteCount  > 0) {
          Serial.print("Command     : ");
          Serial.println(Command);
          Serial.print("Data        : ");
          Serial.println(Data);
         } 
       
}

Being creative in electronics as a hobbyist

I am not an Electronics Engineer. I am not officially trained and have no related certifications. I am however, what I would call “experienced”. I was introduced to electronics as a hobby in the late 1960’s as a kid in home where electronics was paying the bills, so to speak. My father was, at the time, an electronics systems technician working for a large military contractor.

It probably started the day I “went to work” with him and he showed me the project he was working on… It was a missile launch system loaded with cool control panels and of course, Nixie number indicator tubes.

So, at around age 13 or 14, I wanted to know how all this stuff worked. Unlike today, we had nothing like the Internet so find out how stuff worked involved going to the library and reading books or the magazines of day like Popular Electronics. My dad also had a collection of technical books and schematics that I would read over and over again.

So it started to become clear to me that a “designer” would use a collection of parts and arrange them in a particular way to take advantage of their physical “laws” to achieve a particular result. It also became clear that the characteristics of each individual part were as important as how they were assembled together. A particular device is chosen based on the effect it’s value and parameters have on the overall assembly. It sometimes became clear to me that some parts are chosen based on availability and commonality making them what the assembly is built around.

In my case, I started to understand schematics and the meaning of the symbols rather quickly. I also discovered that unless I truly know what a part does, I don’t try to design with it. This lead to the start of a collection of component “data books”. Logically, these are no longer produced as it requires dead trees and we are much better served by online PDF files known as “Data Sheets”.

So, what does it mean to be a hobbyist?

Well, we are actually able to willfully misuse parts in ways they were never intended to be used, which is a luxury a professional designer doesn’t have. We don’t have a boss looking over our shoulder saying “Is it done yet? We are on a schedule here!”. In short, we can play. We can be creative. We can build and not be driven by time constraints and production budgets. We can have fun.

Where to start?

1) Try to learn some electronics theory. Nothing too deep. You should not have to go far beyond learning OHMS Law to be good enough. Lot of web resources exist already
2) Sketch your ideas out on paper before starting on the breadboard.
3) A solder-less breadboard and some jumper wires
4) Datasheets are king. Don’t try to use a part, especially a transistor or integrated circuit without one
5) Get some tools. You can get a good “temperature controlled” solder station for as little as $14. Wire cutters, needle-nose pliers and solder-sucker are all also high on the list of “should have’s”. A cheap un-controlled “fire-stick” or a “gun” type soldering iron are unsuitable for electronics.

With that out of the way… what’s next?

Find what interests you. For example, even after 50 years, we still use discrete transistors. It is still a major building block in electronics. Learning how they work can be a fun adventure so I’ll tell you about how I learned about transistors. I found a book in the library about transistor “multi-vibrators” and not having a clue what a multi-vibrator was, I started reading it. It turns out, it’s a circuit family based on a design using at least 2 transistors with a feedback path where the state of one transistor affects the state of another. Such a nice place to start. I learned about R/C (resistor/capacitor) interaction and how it could create a time delay and how this R/C behavior could create an oscillator or a circuit that could extend a small pulse into a long one.

Thus began my long journey of learning something new nearly every day… and the start of a fun hobby.