Sunday, May 01, 2016

Commodore VIC-20

The famous VIC-20. Predecessor to the Commodore 64, introduced in 1980 and thus being the very first affordable (US$300,-) colour computer.  Almost three million units were sold at the time, so they are still not very rare.
The unit I got (for €40,-) is in pretty good condition. The case has some inevitable yellow marks, caused by the reaction of UV light with the flame-retardand in the plastic. Something that could be removed (just google for 'RetrOBright')  but I think I'll just leave it like it is and not risk damaging the plastic.
The unit came without any cables, so the first step will be to find out how to connect the monitor. As always, this information is easy to be found. I found a complete overview on Retro Isle this time.
The video is on the 5-pin DIN plug, 2 = GND, 4= Video. 

Unfortunately it does not seem to work.
My small LCD monitor (that works fine with my TRS-80 and Acorn Electron) says 'no signal'. When measuring the video signal on the outside and on the board itself using an oscilloscope it looks good. But even adjusting the output level to the max does not solve the issue.
Just to be sure there is something wrong with it I connected it to the flatscreen television in the living room, only to find that it actually does work....
Looking into this issue I found several references to the fact that the video signal of the VIC is really bad, which did not really matter in those days since the standard television and monitor was pretty tolerant, but is a problem for our modern, all digital, LCD screens.
On the 'Denial WIKI' there are a few suggestions on how to improve video output which might be worth trying.

Monday, April 25, 2016

Acorn Electron

For only €20,- I purchased an Acorn Electron in excellent condition. The Electron was developed around 1982 as a direct competitor to the the Sinclair Spectrum, and even though it had some drawbacks it was sold in such large quantities that it is not to rare today. No need to tell the history, since there is already an excellent article on The Register about that.
Although this machine was not really on  my wish-list it's a pleasant surprise. First it's very compact and well-built. The housing is made of solid plastic, which even after 30 years does not show any colouring or scratches.
The keyboard is pretty good, and although most keys have multiple functions they are not crammed with it like the Commodore 64 or Sinclair spectrum.
The inside looks equally good. Just four screws have to be taken out to reveal a very clean motherboard and separate power supply .
They were very serious about the shielding against electromagnetic radiation, as clearly visible on the keyboard side.  

The user guide is excellent. It starts (as many user guides from this era) with an explanation of what a computer is: 

"A computer is a general purpose electronic machine that can be instructed to do a great variety of things - play games, perform complex calculations, store and retrieve information, display graphs and so on."
(You can read the whole guide on Acorn Electron World .  )

What surprised me is the possibilities of the Basic interpreter. It actually has named functions and procedures, a 'repeat..until' loop, quite advanced graphic functions and a built-in assembler to write machine code. And this machine code is definitely worth checking out, because the Basic is not really fast...

Enabling Colour on the composite video output

After working with it for while having it connected to a LCD monitor I noticed that it did not display colour. Initially worried that maybe the video circuit was damaged, I soon found out that this is intentional. The standard composite video output is set to black and white, but there is a link on the board that can be made to enable the colour signal. 
It's marked 'LK4', and I just soldered a link on it. After that the monitor shows colour as expected, but I do have the impression that the letters are less crisp (which was probably the reason for Acorn to have just black and white as a default)

Loading software

The machine came without a cassette recorder, but it should work with any standard audio recorder. Which in these days can be replaced by simple recording / replay software on a PC. I used Audacity to record a simple Basic program, and after fiddling a bit with the audio levels (for recording as well as playback) it worked fine.
Loading standard software appeared a bit harder. Almost all software published for the Electron is available online, usually in the '.UEF' ('Universal Emulator Format') file format. A very simple Windows program named FreeUEF can be used to either replay it as audio or to convert it to a  .WAV file that can be replayed by other software. The last solution did not really work for me. Replaying the created .WAV files using Audacity always gave an error after reading the first block. All other blocks seem to load fine, but the program will not run on the Electron.

Finally I used an Android App on my tablet named 'TapDancer'. This works flawlessly and because it actually looks like a Commodore Datasette it adds a little extra to the retro-feeling...

And if you want to go a step further, there is the GoSDC  expansion module that lets you load programs from an SD card. But let's face it: compared to loading programs using the tape interface it only saves you a minute during the loading itself. So unless you switch programs every 5 minutes I doubt if this is really worth it.

Tuesday, November 03, 2015

Go for C64 - Part II - The Arduino Leonardo solution

After trying to turn my C64  into a USB keyboard the whole project ended in a cupboard for a year at 90% completion. In the end the whole PICAXE - Arduino Pro Micro combination felt a bit clumsy.
Then I recently stumbled on a blogpost where someone connects a ZX81 keyboard to the Arduino Leonardo, and I found a cheap (€12,-) Leonardo-clone so I decided this was the way to go.

The board came with front headers, which makes connecting the keyboard super easy.
This is the C64 Keyboard matrix: ( diagram from the 'WaitingForFriday' blog)

Corrected C64 Keyboard matrix and keyboard connector diagrams
It is connected to the Arduino as follows:

A - D0
B - D1
C - D2
D - D3
E - D4
F - D5
G - D6
H - D7
0 - D8
1 - D9
2 - D10
3 - D11
4 - A0
5 - A1
6 - A2
7 - A3

The code can be a mix of the code from 'Biosrythm' and TechTonic . :

#include <Keyboard.h>

// ZX81 USB Keyboard for Leonardo
// (c) Dave Curran
// 2013-04-27

// Modified with Function keys by Tony Smith
// 2014-02-15
// Adapted for use with Commodore 64 Keyboard by Cees Meijer
// 2015-11-04
// Enable the debug mode (serial output) by keeping F7 pressed when 
// starting the program
// Special Commodore graphic characters are not implemented

#define NUM_ROWS 8
#define NUM_COLS 8

#define SHIFT_ROW 3
#define SHIFT_COL 1

#define RSHIFT_ROW 4
#define RSHIFT_COL 6

#define F7_ROW 7
#define F7_COL 7

#define DEBOUNCE_VALUE 100
#define REPEAT_DELAY 500

// Keymap for normal use

byte keyMap[NUM_ROWS][NUM_COLS] =
  {'1', '3', '5', '7', '9', '+', '$', KEY_BACKSPACE},
  {KEY_LEFT_ARROW, 'w', 'r', 'y', 'i', 'p', '*', KEY_RETURN},
  {'~', 'a', 'd', 'g', 'j', 'l', ';', KEY_LEFT_ARROW},
  {'~', 0  , 'x', 'v', 'n', ',', '/', KEY_UP_ARROW},
  {' ', 'z', 'c', 'b', 'm', '.', 0  , KEY_F1},
  {'~', 's', 'f', 'h', 'k',':', '=' , KEY_F3},
  {'q', 'e', 't', 'u', 'o', '@', KEY_UP_ARROW, KEY_F5},
  {'2', '4', '6', '8', '0', '-', '~', KEY_F7}

// Keymap if Shift is pressed

byte keyMapShifted[NUM_ROWS][NUM_COLS] =
  {'!', '#', '%', '\'', ')', '+', '$', KEY_BACKSPACE},
  {KEY_LEFT_ARROW, 'W', 'R', 'Y', 'I', 'P', '*', KEY_RETURN},
  {'~', 'A', 'D', 'G', 'J', 'L', ']', KEY_RIGHT_ARROW},
  {'~', 0  , 'X', 'V', 'N', '<', '?', KEY_DOWN_ARROW},
  {' ', 'Z', 'C', 'B', 'M', '>', 0  ,KEY_F2},
  {'~', 'S', 'F', 'H', 'K','[', '=', KEY_F4},
  {'Q', 'E', 'T', 'U', 'O', '@', KEY_UP_ARROW, KEY_F6},
  {'"', '$', '&', '(', '0', '-', '~', KEY_F8}
// Global Variables

int debounceCount[NUM_ROWS][NUM_COLS];
int altKeyFlag;
bool serial_output;

// Define the row and column pins

byte colPins[NUM_COLS] = {0,1,2 ,3 ,4 ,5 ,6 ,7}; // A,B,C,D,E,F,G,H
byte rowPins[NUM_ROWS] = {8,9,10,11,A0,A1,A2,A3};


void setup()
  // Set all pins as inputs and activate pull-ups
  serial_output = false;
  for (byte c = 0 ; c < NUM_COLS ; c++)
    pinMode(colPins[c], INPUT);
    digitalWrite(colPins[c], HIGH);
    // Clear debounce counts
    for (byte r = 0 ; r < NUM_ROWS ; r++)
      debounceCount[r][c] = 0;
  // Set all pins as inputs
  for (byte r = 0 ; r < NUM_ROWS ; r++)
    pinMode(rowPins[r], INPUT);
  // Function key is NOT pressed
  altKeyFlag = ALT_KEY_OFF;
  pinMode(rowPins[F7_ROW], OUTPUT);
  if (digitalRead(colPins[F7_COL]) == LOW) serial_output = true;
  // Initialise the keyboard
  if (serial_output )


void loop()
  bool shifted = false;
  bool r_shifted = false;
  bool keyPressed = false;
  // Check for the Shift key being pressed
  pinMode(rowPins[SHIFT_ROW], OUTPUT);
  if (digitalRead(colPins[SHIFT_COL]) == LOW) shifted = true;
  pinMode(rowPins[RSHIFT_ROW], OUTPUT);
  if (digitalRead(colPins[RSHIFT_COL]) == LOW) shifted = true;
    pinMode(rowPins[SHIFT_ROW], INPUT);
    pinMode(rowPins[RSHIFT_ROW], INPUT);
    for (byte r = 0 ; r < NUM_ROWS ; r++)
      // Run through the rows, turn them on
      pinMode(rowPins[r], OUTPUT);
      digitalWrite(rowPins[r], LOW);
      for (byte c = 0 ; c < NUM_COLS ; c++)
        if (digitalRead(colPins[c]) == LOW)
          // Increase the debounce count
          // Has the switch been pressed continually for long enough?
          int count = debounceCount[r][c];
          if (count == DEBOUNCE_VALUE)
            // First press
            keyPressed = true;
            pressKey(r, c, shifted);
          else if (count > DEBOUNCE_VALUE)
            // Check for repeats
            count -= DEBOUNCE_VALUE;
            if (count % REPEAT_DELAY == 0)
              // Send repeat
              keyPressed = true;
              pressKey(r, c, shifted);
          // Not pressed; reset debounce count
          debounceCount[r][c] = 0;
    // Turn the row back off
    pinMode(rowPins[r], INPUT);
    digitalWrite(rowPins[RSHIFT_ROW], LOW);
    digitalWrite(rowPins[SHIFT_ROW], LOW);

void pressKey(byte r, byte c, bool shifted)
  // Send the keypress
  if (serial_output) 
  byte key = shifted ? keyMapShifted[r][c] : keyMap[r][c];

  if (serial_output)
   if (key > 0){ Serial.write(key);}
   if (key > 0 ) Keyboard.write(key);

Wednesday, May 06, 2015

The 'Makr-B-Bot' Part 1: Getting started

When the 3D-Printing hype started a few years ago with the RepRap and it's followers, it immediately considered building one. By that time however it was not really easy to collect the parts. People were building their own electronics, frames and extruders from scratch which included a lot of experimenting and tinkering to get it right. Round the same time I ran into a product called 'MakerBeam', an aluminium T-Slot profile for small constructions. This seemed like the right framework for a 3-D printer so I bought the starter kit. Bolted a few parts together and decided it would still be a lot of work to build a printer from this. So the kit ended up in a closet, and I have not used it since..

In the following years the 3D printer market exploded, and at some point even got mainstream with little €1000,- plug and play printers you could buy at the supermarket. So I lost interest.  The idea of building one did stick at the back of my mind however. And over time I did collect some parts like a set of stepper motors, some extra Makerbeams and  some electronics.

Until recently I got inspired by pictures of the Printrbot Simple Maker kit . This amazingly simple design is probably the most minimalistic printer possible, yet it performs remarkably well for it's price, which is as low as US$350 for a complete kit. Now US$350,- is absolutely a good price for the full kit, but unfortunately that only works if you live in the USA. Once you get it to Europe the total price has become a whopping €550,- (= US$ 590,- !) which more or less defies the idea of a 'cheap DIY printer'. 

Since this is an 'open source' printer so it is possible to download the drawings and make the plywood parts yourself, but that would still be quite expensive for a single unit.
While looking for additional pictures of the PrintrBot design I also found the R360 Printer by Replicator warehouse :

This looks almost identical, but they chose a rotating bed to print on. Not sure if this is good idea, and it's definitely not supported by standard software. Also I think it's a little bit too much plastic...

So I wondered if it would be possible to build this specific design using standard Makerbeam parts.

And I did not want to spend too much money on it so I spend quite some time to find the cheapest parts....


  • Makerbeam starter kit.+ extra set of right angle brackets. ( €100 )
  • Acme rod (trapezoidal thread) with nut . ( €20 ). This one used to be hard to get, but nowadays most 3D printer shops sell the standard 30 cm version that is used in the RepRap Mendel  (MakeMendel,VanAllesEnMeer (Dutch) )
  • Flexible coupling 5 mm to 8 mm.n (€6,50) Any 3D printer shop has these in stock
  • 2 pcs Aluminium pully, T2.5 (€ 6,50)
  • 1 m. of T2.5 5mm Timing belt (€4,50)
  • 12 pcs.  LM8UU linear ball Bearings (€12,-) (€1,- / each is really good deal ! Kromhout Electronixs (Dutch))
  • 3 pcs. NEMA 17 stepper motors (€30,- (special package deal, might be hard to get them that cheap now..))
  • Funduino Mega 2560 R3 Module (Arduino Mega compatible board) (€15)
  • RAMPS 1.4 interface board (€18, including the Motor Drivers))
  • 4 pcs. 4988 Motor Driver (Polulu or compatible) 
  • Geeetech MK8 All Metal 3D Printer Extruder (DealExtreme) (€45)
  • AT Power supply (second hand, from an old PC)
  • Lots of Ty-Raps
  • 16 Hose clamps, 12-22 mm (€10)
  • 2 pcs. 1m. 8mm.  Steel Rod (€15) ( Printed Parts, IJzershop (Dutch) )
  • Heated bed (€15)
  • 12V/ 20 A Power Supply (€24,-)
Total: € 321,-
 (Actually a little less since not the whole MakerBeam kit is used)

Again, the US$350,- for the the PrintrBot Simple kit seems like a bargain. You probably have to buy all parts in really large quantities to get that low. Not to mention the US$179,- TIKO 3D , or the US$199 Genesis UNO  ..

Now everything is here, let's start building...