Using a Max7219 8×8 LED Matrix with an ATTINY85, like Trinket or DigiSpark

While waiting for part two of the handheld construction article, I thought I’d give you a little distraction about interfacing an ATTINY85 to an 8×8 LED Matrix using the Max7219 chip.

ATTINY85LEDMatrix1Been working on getting either a DigiSpark or Trinket to work with one of my 8×8 LED matrix displays. Connection is simple, but the maxmatrix library doesn’t seem to like the ATTINY85 processor. So, I went looking for something that did or, at least, getting enough knowledge to bit bang my way to displaying SOMETHING on the little display. Well, I found some code to do this, but it is not very pretty and doesn’t do enough. However, it does give a good demo of how to make these arrays do something and, even better, work with the confines of the ATTINY85 processor.
The code shows how turn on and off pixels (a specific LED in the matrix, to be more precise) and send a ‘bitmap’ to the display.
Cool stuff. Could be another game or, perhaps, a temperature display, mood indicator, etc.

You can grab the code I used (middle of the page) here……/max7219-8×8-dot-matrix-led-drive…

FYI-To connect it:
PB0 -> DIN
PB1 -> CS
PB2 -> CLK
+5 -> VCC

Pretty easy. ATTINY85LEDMatrix21

The code I found puts a smiley face, inverts the screen, frowny face, etc. up on the display. I took out the inversion as it takes too much time.  This code, which is unattributed as the poster on the AVR forum did not credit the code, is a good start, but needs work.  I thought about modifying it to handle ASCII text, but that will be a ways off yet. I have several things to finish up before then. 

I’d love to see what you can do with this, so drop us a note in the comments or send me an email and I’d be happy to write it up and post it here.


  One MAX7219 connected to an 8x8 LED matrix.

#include <avr/io.h>
#include <util/delay.h>

#define CLK_HIGH()  PORTB |= (1<<PB2)
#define CLK_LOW()   PORTB &= ~(1<<PB2)
#define CS_HIGH()   PORTB |= (1<<PB1)
#define CS_LOW()    PORTB &= ~(1<<PB1)
#define DATA_HIGH() PORTB |= (1<<PB0)
#define DATA_LOW()  PORTB &= ~(1<<PB0)
#define INIT_PORT() DDRB |= (1<<PB0) | (1<<PB1) | (1<<PB2)

uint8_t smile[8] = {

uint8_t sad[8] = {

void spi_send(uint8_t data)
    uint8_t i;

    for (i = 0; i < 8; i++, data <<= 1)
  if (data & 0x80)

void max7219_writec(uint8_t high_byte, uint8_t low_byte)

void max7219_clear(void)
    uint8_t i;
    for (i = 0; i < 8; i++)
  max7219_writec(i+1, 0);

void max7219_init(void)
    // Decode mode: none
    max7219_writec(0x09, 0);
    // Intensity: 3 (0-15)
    max7219_writec(0x0A, 1);
    // Scan limit: All "digits" (rows) on
    max7219_writec(0x0B, 7);
    // Shutdown register: Display on
    max7219_writec(0x0C, 1);
    // Display test: off
    max7219_writec(0x0F, 0);

uint8_t display[8];

void update_display(void)
    uint8_t i;

    for (i = 0; i < 8; i++)
  max7219_writec(i+1, display[i]);

void image(uint8_t im[8])
    uint8_t i;

    for (i = 0; i < 8; i++)
  display[i] = im[i];

void set_pixel(uint8_t r, uint8_t c, uint8_t value)
    switch (value)
    case 0: // Clear bit
  display[r] &= (uint8_t) ~(0x80 >> c);
    case 1: // Set bit
  display[r] |= (0x80 >> c);
    default: // XOR bit
  display[r] ^= (0x80 >> c);

int main(void)
    uint8_t i;

  // Invert display
//  for (i = 0 ; i < 8*8; i++)
//  {
//      set_pixel(i / 8, i % 8, 2);
//      update_display();
//      _delay_ms(10);
//  }



Getting video out from your Adafruit Trinket or DigiSpark (or ANY ATTINY85)

11224347_913681192034970_90837413382715523_oWhile pouring through some videos and posts on just what the tiny little ATTiny85 chip can do, I ran across a HackADay post about someone generating NTSC video on VHF channel 3 (US channel 3.)  I was intrigued.  So, I tried it and got mixed results and, as I have only a couple of old analog sets, I thought it was kind of impractical to pursue, but cool anyway.  So, I wondered if just composite out would be better and, to my delight, the same person who posted the video also had done composite out with an ATTiny84.  It should work on the 85 as well, and, it does.

So, I found his code and downloaded it.  Mr. Lohr is a GENIUS, plain and simple.  Thank you, sir!

The code did not work well at first. I had to tweak it a bit to work with my hardware, especially the little monitor.  It still is not perfect, the video is not centered, but is fairly steady and bright…my first attempts were not very bright and not very steady. I am guessing it needs to be tweaked for the monitor it will be used on, but I have not tested on more than one.

All you need is something like a Trinket from Adafruit or a digispark. I used both, but destroyed the digispark when I attempted to use an external power source.  It does not like more than five volts.  Specs say 3.5 to 12volts, I used 9. My mistake. 12182942_913681798701576_4759339394040268204_o

The Trinket works great. I am using the 5volt version with USB.  Any ATTiny85 based controller should work, though.

Connecting it is simple: Pin 3 to video ground, Pin 4 to video center pin.  Download the code to your device, connect it to the monitor and reset it. You should see the video demo.

Now, there are some major caveats:

  • it, so far, only does text
  • you have 13 characters by 6 lines
  • character spacing is mono
  • there’s no video memory, each frame is drawn on the fly
  • the ‘video memory’ is simply a string array
  • there is no formatting
  • the character set is stored in flash

So, why bother with such limitations? Well, for starters, cheap composite monitors are easy to get WP_20151025_11_19_10_Rich_LIand use and the Trinket/digispark are both under ten bucks, so you can have an application with video out for very little money.  If nothing else, this is a great lesson in how video works. Charles Lohr did a fantastic job with the code.  He’s a genius. Did I mention that?

Any way, the code is posted below.  Let us know if you get it working and what you do with it.



    Copyright (C) 2014 <>< Charles Lohr

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
    to deal in the Software without restriction, including without limitation
    the rights to use, copy, modify, merge, publish, distribute, sublicense,
    and/or sell copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.


#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
#include <util/delay.h>
#include <avr/pgmspace.h>
#include "ntscfont.h"


void delay_ms(uint32_t time) {
  uint32_t i;
  for (i = 0; i < time; i++) {

#define NOOP asm volatile("nop" ::)

void NumToText( char * c, uint8_t a )
    c[0] = (a/100)+'0';
    c[1] = ((a/10)%10)+'0';
    c[2] = (a%10)+'0';
    c[3] = 0;
void NumToText4( char * c, uint16_t a )
    c[0] = (a/1000)+'0';
    c[1] = ((a/100)%10)+'0';
    c[2] = ((a/10)%10)+'0';
    c[3] = (a%10)+'0';
    c[4] = 0;


int main( )

    CLKPR = 0x80;    /*Setup CLKPCE to be receptive*/
    CLKPR = 0x00;    /*No scalar*/

    PLLCSR = _BV(PLLE) | _BV( PCKE );
//    PLLCSR |= _BV(LSM);

    DDRB = _BV(1);

    DDRB |= _BV(3);
    DDRB |= _BV(4);
    PORTB |= _BV(1);

    TCCR1 = _BV(CS10);// | _BV(CTC1); //Clear on trigger.
    GTCCR |= _BV(PWM1B) |  _BV(COM1B0);// | _BV(COM1B1);
    OCR1B = 2;
    OCR1C = 3;
    DTPS1 = 0;
    DT1B = _BV(0) | _BV(4);

    TCCR0A = 0;
    TCCR0B = _BV(CS01);
    TIMSK |= _BV(TOIE0);

OSCCAL = 215;

//    OSCCAL=186;

#define POWERSET

#define NTSC_HI  {    DDRB=0;}
#define NTSC_LOW {    DDRB=_BV(4); }
#define NTSC_VH  {    DDRB=_BV(3); }
#elif defined( POWERSET2 )
#define NTSC_VH  {    DDRB=0;}
#define NTSC_LOW {    DDRB=_BV(4)|_BV(3); }
#define NTSC_HI  {    DDRB=_BV(3); }
#elif defined( POWERSET3 )
#define NTSC_VH  {    DDRB=0; }
#define NTSC_HI   { DDRB=_BV(3); }
#define NTSC_LOW   {    DDRB=_BV(4)|_BV(3); }

//Experimental mechanisms for changing power. Don't work.
#define NTSC_VH  {    OCR1C = 3; TCNT1 = 0; }
#define NTSC_HI  {    OCR1C = 6; TCNT1 = 0;}
#define NTSC_LOW {    OCR1C = 0; TCNT1 = 0;}

    uint8_t line, i;

    #define TIMEOFFSET .12 //.12
    #define CLKOFS .12

    uint8_t frame = 0, k, ctll;
    char stdsr[8*13];
    sprintf( stdsr, "Fr: " );
    sprintf( stdsr+8,  "HalfByte" );
    sprintf( stdsr+16, "  Blog  " );
    sprintf( stdsr+24, "        " );
    sprintf( stdsr+32, " Trinket" );
    sprintf( stdsr+40, "AdaFruit" );
    sprintf( stdsr+48, "        " );
    sprintf( stdsr+56, "        " );
    sprintf( stdsr+64, "        " );
    sprintf( stdsr+72, "        " );
    sprintf( stdsr+80, "        " );
    sprintf( stdsr+88, "        " );

    ADMUX =/* _BV(REFS1)  |  _BV(ADLAR) | */ 1; //1 = PB2
    ADCSRA = _BV(ADEN) | _BV(ADSC) | _BV(ADATE) | _BV(ADPS2) | _BV(ADPS1);

#define LINETIME 21 //Linetime of 7..20 is barely valid. So,
//#define WAITTCNT while(TCNT0);

//#define WAITTCNT while(!(TIFR&_BV(TOV0)));
#define WAITTCNT sleep_cpu();

//#define WAITTCNT fintcnt();


    uint16_t ovax; //0..1024 = 0...5v
    uint8_t  msd;
    uint8_t  lsd;


        //H = 1./15734.264 = 63.555 / 2 = 31.7775
        for( line = 0; line < 6; line++ )
        { NTSC_LOW; _delay_us(2.3-TIMEOFFSET); NTSC_HI; _delay_us(29.5-TIMEOFFSET-CLKOFS); }
        for( line = 0; line < 6; line++ )
        { NTSC_LOW; _delay_us(27.1-TIMEOFFSET); NTSC_HI; _delay_us(4.7-TIMEOFFSET-CLKOFS); }
        for( line = 0; line < 6; line++ )
        { NTSC_LOW; _delay_us(2.3-TIMEOFFSET); NTSC_HI; _delay_us(29.5-TIMEOFFSET-CLKOFS); }

        for( line = 0; line < 39; line++ )

            //Do whatever you want.
            //sprintf( stdsr, "%d", frame );
            switch (line)
            case 0:
                NumToText( stdsr+4, frame );
            case 1:
                ovax = ADC;
                ovax = ovax * 49 + (ovax>>1);
            case 2:
                NumToText( stdsr+24, ovax/1000 );
                stdsr[27] = '.';
            case 5:
                NumToText4( stdsr+27, ovax );
                stdsr[27] = '.';



        for( line = 0; line < 2; line++ )

        for( line = 0; line < 220; line++ )
            NTSC_LOW; _delay_us(4.7-TIMEOFFSET);
            NTSC_HI; _delay_us(8-TIMEOFFSET-CLKOFS);

//#define LINETEST
            NTSC_VH; _delay_us(8-TIMEOFFSET-CLKOFS);
            NTSC_HI; _delay_us(44.5);
            ctll = line>>2;
            for( k = 0; k < 8; k++ )
      // draw the character, one pixel at a time
            uint8_t ch = pgm_read_byte( &font_8x8_data[(stdsr[k+((ctll>>3)<<3)]<<3)] + (ctll&0x07) );
            for( i = 0; i < 8; i++ )
                if( (ch&1) ) //if pixel is dark...
                    NTSC_HI;  // pixel is lit
                NOOP; NOOP; NOOP; NOOP;


            NTSC_HI; //_delay_us(4.7-TIMEOFFSET-CLKOFS);

//        NTSC_HI; _delay_us(46-TIMEOFFSET-CLKOFS);

//            NTSC_VH; _delay_us(32-TIMEOFFSET-CLKOFS);
//            NTSC_HI; _delay_us(19.8-TIMEOFFSET-CLKOFS);
    return 0;


Download the original code and the font file here. You will need the font file to make this work.

Mr. Lohr’s YouTube Channel

A Spark of Life: More DigiSpark fun

WP_20151019_22_42_59_Pro__highresI recently wrote about the cool little DigiSpark ATTiny 85 controller board. This little USB wonder, like the AdaFruit Trinket, is based on the ATTiny85 Microcontroller and has limited I/O, memory and is cheap, very cheap.

One thing it is not short on, however, is uses. This little thing can be used for a variety of things, including games and control applications.  For any use, though, you will need some kind of input and some kind of output.  In a previous post, I postulated about porting my ‘Battlestar Galactica’ game to the DigiSpark from the Trinket.  So, here are the results of that endeavor and some other things as well.

For the backstory of the game and why I wrote it, check out this post. I’ll wait.

Read it?  Cool.WP_20151019_22_44_34_Pro__highres

Ok, so there are few differences between the Trinket and the DigiSpark, other than size.  The way you program it is very similar and the pins are nearly identical.  The way you talk to things, is, however, a little different.

The Trinket needed SoftwareSerial. We don’t here, we just use DigitalRead and DigitalWrite and Serial.write to read the button and write to the screen.

The display is a 16×2 Serial LCD from Parallax.  The button is actually a ‘controller’ I built a couple of years ago for my game console. I did not use it for that, opting for the Wii Nunchuck instead.  So, the controller has three buttons that would be used for left, right and ‘fire’ or action.  Here, they just return a 0 if pressed and a 1 when ‘open’.  The code periodically polls the controller for a press and then acts on the press to evaluate a hit or miss.


Now, one of the problems I had was the lack of GROUND pins. So, I made a ground bus, a four pin strip with a wire connecting all four pins. I then connected this to ground on the DS and the button and the LCD as well are connected to this bus. I have one free ground pin.  Well, what I did not realize was that you can use any pin for ground.  While I did not change my connections, I find this pretty cool.

TIP! To use a free pin as ground:

(From the wiki)

You can use an I/O pin as a ground/+5V if you have some left and the current that flow in it is low (a few milliamps if you want the pin to stay around 0V/+5V. If you don’t care about the exact voltage you can go up to 40mA per pin according to the datasheet but it’s good to keep a safety margin).

Configure the pin as an output and set its value to either LOW or HIGH (for ground or +5V

#define button 0
#define gnd 2
void setup() {                
  pinMode (button, INPUT);
  digitalWrite (button, HIGH); // enable pullup
  pinMode(gnd, OUTPUT);
  digitalWrite (gnd, LOW); // use this pin as a ground

For much more information and tips, go to the wiki, located here.

The game code is below.

Come back for more on this cool little device.  Since it is capable of serial i/o, I’m thinking of using the Bluetooth Serial module and connecting the DS to one of my HalfByte Consoles running the graphical serial software for video display from the DS.


Game Code:

#include <TinyPinChange.h>

 // globals
 int  cylonpos;
 int  oldcylonpos;
 int  cyDirection;
 int  button;
 int  posStart;
 int  lin2Start;
 int  bsgpos;
 // special characters
 int  bsg;
 int  cylon;
 // total number of torpedos the ship has left
 int  tShots=10;
 // the setup routine runs once when you press reset:
 void waitforbutton();
 void moveCylon();
 void setup() {  // initialize the digital pin as an output.  
   //define the ship character
   // baddies

   Serial.write(uint8_t(0x0));//to handle a goofy issue with '0'
 // the button is on pin 0  
 // the initial direction is right
 } // the loop routine runs over and over again forever:
 void loop() {
  int score;
  Serial.write(12); // clear the screen and show the instructions
  Serial.println("Shoot the Cylon\n");
  Serial.println("press btn strt");
  // wait for the button
  // define somethings before we start the game loop
  lin2Start=148; // the baddies appear on line 1
  posStart=128;  // the good guys on line 2
  randomSeed(analogRead(0)); // gen a random seed
  bsgpos = 8;  // our ship starts in the middle of the sector
  cylonpos=random(0,15); // baddies warp in at a random spot
  Serial.write(12);  // clear screen
  Serial.write(17);  // turn on backlight so we can see
  Serial.write(posStart + cylonpos);  // uh oh...the Cylon appeared!
  Serial.write(bsg); // and here we are
  // begin the game 
    /* Game loop */
    int button;
    Serial.write(22); // kill the cursor
    button=digitalRead(0);  // check the button
    if(button==0){ // torpedo fired?
      if(cylonpos==bsgpos){ // Hit?
        Serial.write(132); // center 'Hit' on screen
        Serial.print("** HIT **");
        score ++;  // update score
        Serial.write(213); // noise (C at half note, 3rd scale)
        Serial.write(215); // play the note
        if(score==10){  // did we win?
           Serial.write(12); // clear screen
           Serial.write(128);// start at beginning
           Serial.print("You have saved\nthe Galactica.");
           loop();  // start game again
        delay(3000); // did not win yet
        Serial.write(12); // clear screen
        Serial.write(lin2Start); // move cursor to beginning of line
        Serial.write("Score:");  // put up score
        Serial.write(lin2Start+bsgpos); // Since we shot the Cylon, we have to leave the sector, so...
        Serial.write(0x20); // go into hyperdrive and erase the BSG
        bsgpos=random(9,15);  // calculate new position
        Serial.write(lin2Start+bsgpos); //...and, we are here
        cylonpos=random(0,15); // Damn, they found us!
      tShots --; // decrement our torpedo inventory
      if(tShots<1){ // out of ammo?
        Serial.write(12);  // clear screen
        Serial.write(posStart); // start at beginning of line
        Serial.print("The Cylons win.\n");
        int count=1;
        // show animation of our ship exploding
        while (count<10){
        loop(); // Play again
void moveCylon(){
  // sneaky Cylons...they show up anywhere!
  if (random(0,6)>3){
      //Cylon warped
  cylonpos += cyDirection; // figure out which way to move
  if (cylonpos>15){
  if (cylonpos<0){
  // erase from old spot

void waitforbutton(){
  int button;
  while(button==1){     //wait for button press

The Mighty ATTiny85 and DigiSpark

Microcontrollers are lots of fun to play with as well as to build useful things.  They come in all sizes, shapes and varieties.  I am always, however, intrigued with the tiny controllers, like AdaFruit’s Trinket.  Well, the latest one I’ve started to tackle is the DigiSpark.  The DigiSpark is small and comes in several types. I am using the USB flavor. This little guy is on a very small board, about the size of a nickel, and is, itself, a USB dongle.

WP_20150928_23_59_09_Pro (2)

It features six I/O lines, plus power and ground pins.  This thing is a little bit more versatile than the original Trinket, but not much more. The USB version has the added advantage of being a USB dongle itself, meaning you can build a project that plugs into a USB port and act as an external controller. You don’t need USB, once you have programmed it, the power and ground pins can be used to power the device.

The nice thing about the DigiSpark is that you can use the Arduino IDE and SOME of the libraries to program the device.  There is a nice tutorial on setting up a newer release of the IDE and add DigiSpark support.

In a nutshell:

  1. Start the IDE (Install 1.6.x if you don’t already have it installed)
  2. Click FILE, then PREFERENCES
  3. in the Additional Boards Manager URL’s box, enter:
  4. Click OK
  5. Click Tools, then BOARDS
  6. Select Board Manager and then Contributed
  7. In the dialog box that pops up, select DIGISTUMP AVR BOARDS
  8. Click Install
  9. Close the Board Manager
  10. You should now see the DigiSpark boards in the IDE

The thing that tripped me up was uploading a sketch.  I didn’t realize that you don’t need to have the device plugged in prior to uploading (you are told this, but it didn’t sink in.)  Once I unplugged the device, clicked upload and THEN plugged it in, it worked like a charm.

So, now I have to figure out what I want to do with this cool little device. 

But, wait…I still have not really said anything about the device, what it has on it, etc.

It is based on the ATTiny 85 and features six I/O pins:

Pin outs:

    • All pins can be used as Digital I/O

    • Pin 0 → I2C SDA, PWM (LED on Model B)
    • Pin 1 → PWM (LED on Model A)
    • Pin 2 → I2C SCK, Analog
    • Pin 3 → Analog In (also used for USB+ when USB is in use)
    • Pin 4 → PWM, Analog (also used for USB- when USB is in use)
    • Pin 5 → Analog In

The ATTiny 85 specs:

  • 8 Bit Data Bus
  • 20 MHz Max Clock Frequency ( w/ external crystal )
  • 8 kB Program Memory Size
  • 2.7 V to 5.5 V Operating Supply Voltage
  • 6 I/O Pins
  • 512 bytes of RAM


Two things you cannot do from the IDE: burn the bootloader and use the serial monitor. Some libraries will work, most will not.  There is no short circuit or reverse polarity protection, so be careful or you will certainly destroy the board, and, if connected via USB (which it really should not be if using external power) the computer could be damaged as well.


The IDE, as with other Arduino’s, displays the compiler and upload progress in the text area below the coding window.  Several rather bothersome messages can show, but, not to worry, it is normal. See my sample output below.

Sketch uses 668 bytes (11%) of program storage space. Maximum is 6,012 bytes.
Global variables use 9 bytes of dynamic memory.
Running Digispark Uploader…
Plug in device now… (will timeout in 60 seconds)
> Please plug in the device …
> Press CTRL+C to terminate the program.
> Device is found!
connecting: 16% complete
connecting: 22% complete
connecting: 28% complete
connecting: 33% complete
> Device has firmware version 1.6
> Available space for user applications: 6012 bytes
> Suggested sleep time between sending pages: 8ms
> Whole page count: 94  page size: 64
> Erase function sleep duration: 752ms
parsing: 50% complete
> Erasing the memory …
erasing: 55% complete
erasing: 60% complete
erasing: 65% complete
>> Eep! Connection to device lost during erase! Not to worry
>> This happens on some computers – reconnecting…
>> Reconnected! Continuing upload sequence…
> Starting to upload …
writing: 70% complete
writing: 75% complete
writing: 80% complete
> Starting the user app …
running: 100% complete
>> Micronucleus done. Thank you!

Micronucleus is the name of the bootloader.  The disconnect message was a little disturbing, but not a problem.

Maybe I’ll adapt my Battlestar Galactica LCD game to this thing…

Here is a link to the Trinket posts on the blog. It is very similar to the DigiSpark.

digiStump is the maker of the device and they have other products as well. Take a gander around their site. There is a nice Wiki page and forums.

Finally, you can purchase one from Amazon for $4.88 each.  Of course, you can support digiStump by purchasing the device from them, they sell it for $8.95, a little higher than Amazon, but you will be supporting the makers and encourage further development of the product.

It may be small, but this OLED is cute and useful and that little DHT11 really knows when something is hot or not

WP_20140302_013As I stated in a previous post, I have a fetish for displays. Any display. Again, while searching eBay for some parts for my Half-Byte Console project, I found a small, .96 inch OLED display. This little gem uses either SPI, Serial or I2C to interface with your device.  I ordered one and received it a few days ago. As is with most of these cheap parts from China, there was little in the way of documentation or code.  Fortunately, more than one vendor sold them and I found some code, which was good since none of the code I found on the net seemed to work.

This little display is advertised as monochrome, but it really is a two color display.  The top two lines have a yellow background OR yellow foreground and the rest of the screen is blue on black or black on blue.  It was likely out of an old cell phone. To be honest, I’ve not done much research on the history of the screen itself.

Since there are a number of ways to connect the display, which uses the SSD1306, I chose the method in the code that I found:

  1. SCL –>9
  2. SCA –>8

Of course, VCC goes to either 3.3v or 5v and GND to ground.  Once the hardware was connected, I uploaded the code I found. 

The code, found here (but, download it from here, instead), was a simple demonstration and did not come with a very versatile library. Though, it does appear to use the Adafruit GFX library.

Although too small for most of my uses, I wanted to see if it may fit a project I have in mind further down the road. Turns out, it will. So, I then attempted to bang together WP_20140302_016part of that idea using a DHT11 temperature sensor. This sensor also gives the relative humidity. So, I connect the OLED and the DHT11 sensor to an Arduino Mini Pro. The DHT11’s data pin goes to Pin 2 (TX) on the Arduino, and pin 1 goes to 5v and the third pin to GND. I incorporated the DHT code into my OLED demo and then … problems.  Turns out, the OLED library has no built in method to output numerical data.  Remembering my Tiny Basic code, I stole some code from it to output numerical data and…viola! Works like a charm (see photo above.)

At six dollars, the screen isn’t really worth it, as there are better screens out there for the same or even less.  However, if you can these cheaper, they will make great little status displays or even part of a smartwatch or other wearable device.

To use my sample code below, you will need the following libraries installed:

  • SoftwareSerial (should be part of your Arduino installation)
  • IIC_without_ACK.h (use the link above)
  • TinyDHT (download here)
  • avr/power.h (part of your install)

A note about the AdaFruit libraries: While provided free of charge, developing these is not always an easy task (though, it might for Lady Ada) and, as such, you should patronize them whenever you can. They have a great selection and good pricing. I buy quite a bit from them.

The display is also capable of graphical display, but I’ve not yet bothered to try and put an image on the screen. There is a bitmap function in the limited library, but you must convert your image to a C array first.  Take a look at the header file for the OLED font.

have fun!

Sample Code:

#include <SoftwareSerial.h>
#include <IIC_without_ACK.h>
#include “oledfont.c”  

#define OLED_SDA 8
#define OLED_SCL 9

IIC_without_ACK oled(OLED_SDA, OLED_SCL);//9 — sda,10 — scl

* DHT Temperature Sensor
// Connect DHT pin 1 (on the left) of the sensor to +5V
// Connect DHT pin 2 of the sensor to whatever your DHTPIN is
// Connect DHT pin 3 (on the right) of the sensor to GROUND
// include the library code

#include <TinyDHT.h>        // lightweight DHT sensor library
#include <avr/power.h>      // needed to up clock to 16 MHz on 5v Trinket
// Uncomment whatever type sensor you are using!
#define DHTTYPE DHT11     // DHT 11
//#define DHTTYPE DHT22   // DHT 22  (AM2302)
//#define DHTTYPE DHT21   // DHT 21 (AM2301)
#define TEMPTYPE 1        // Use Fahrenheit (0 for celsius)
#define DHTPIN 1          DHT dht(DHTPIN, DHTTYPE); // Define Temp Sensor
static unsigned char *spt;
static void pushb(const char b)
    *spt = b;

static unsigned char popb()
    unsigned char b;
    b = *spt;
    return b;

void printnum(unsigned char x, unsigned char y, int num)
        char st[]=”   “;
    int digits=0;
        int pos=0;
    if(num < 0)
        num = -num;

    do {
        num = num/10;
    while (num > 0);
        while(digits > 0)
         oled.Char_F6x8(x,y, st);
void setup() { 
  dht.begin();  // Initialize DHT Teperature Sensor
void loop() {
  int8_t h = dht.readHumidity();               // Read humidity
  int16_t t = dht.readTemperature(TEMPTYPE);   // read temperature
  if ( t == BAD_TEMP || h == BAD_HUM ) { // if error conditions (see TinyDHT.h)
    oled.Char_F6x8(0,0,”Bad Read on DHT”); //   print error message
  } else {
    oled.Char_F6x8(0,4,”Temp: “);
  delay(2000);  // Read temp every second (2000 ms) (DHT sensor max rate)

Developing a handheld console with Arduino

IMG_3163Since my first exposure to computers and video games, I have wanted to design and build my own. Lacking, however, the resources and knowledge, I thought it would just be a pipedream. Well, fortunately for me, that is not the case.  The technology is to the point where just about anyone can do so and for just a little money and the internet.

Microcontrollers are the key and companies like SparkFun and AdaFruit can supply the bits. If you are really tight on funds or just cheap (like me) you can save a bit by shopping eBay. 

So, what can these microcontrollers do for you? Well, anything you want. And, yes, they can play games.

My original plan was to use something like AdaFruit’s Trinket for the brains and the Nokia 5110 LCD for the screen. Well, the Trinket is just too limited (and, frankly, difficult to program.)  During a lengthy eBay search, I found a bunch of Arduino UNO clones that fit in about the same space as the Trinket, only with more I/O and more memory. I ordered a few of them and then waited almost a month to get them. In the mean time, I used my UNO to start writing code.

IMG_3182Along the way, I discovered the Arduino’s were capable of video, so I spent a few weeks playing with that and have built a game console that I will revisit once my plate is clear. Adafruit and other vendors sell interfaces for the Wii Classic Controller and the Nunchuk…both of which are very easy to code.

Back to the handheld. The Trinket filled in, physically, for my board layout. When the Mini Pro finally arrived, I socketed it and began to wire it up. A strip for the 5110, connector for the speaker and daughter board for the audio amplifier. I wrote up a short demo that married the audio to the graphics library and produced a static Mario splash screen and beginning of the game.  It plays the Super Mario Brothers 2 theme upon startup.1398742_562906223779137_852686949_o

My next tasks include a controller (a matrix of four buttons: Left, Right, Shoot, Start/Stop) and a case. The actual game code will be last. I want the hardware nailed down before I do all of the code.

The system will run off of three 1.5 volt AA batteries. I wanted to use a rechargeable battery, but the added complexity is more than I want to deal with for now.

1425448_569760583093701_1031881671_oThe case is my biggest headache. I was going to use Lego’s, but the cost is more than I want to pay. I have an old Mattel JuiceBox that I will attempt to use. It looks big enough and already contains a battery compartment, holes for the controls and a speaker bay. It’s just really ugly.

I am also building version two of the handheld concurrently. This one will be for myself (the other is for my step son) so it doesn’t need to be as friendly and compact.  At some future point, I may take lessons learned from both and make a third version.  My version will also output video and has a PS/2 keyboard connector.  I have a version of Tiny Basic that will work with this hardware and this will be my portable computer and game console.1267690_572617716141321_1112089022_o

I have, so far, been pretty successful with my creations, even though I have a very rudimentary knowledge of electronics. I know what resistors and capacitors do and an understanding of transistors. More importantly, however, I can read a schematic and everything I’ve done has come from schematics found on the internet. In some cases, I’ve only borrowed parts of the schematic, in other cases, I used a basic schematic from a datasheet (talk about boring) and have put this stuff together on my own.  AdaFruit and SparkFun have terrific user forums and they have been a big help as well.  But, there is one site in particular: Arduino-Info. This site has code, schematics and really easy to understand explanation about each project. It covers basic things like LCD’s, keypad’s, servo motors and basic Arduino. It explains many electronics concepts and has lots of examples. It has been invaluable.

The Nokia 5110 LCD is a low cost and easy to code panel. It is low res, 84 pixels wide by 48 down. It is challenging (I have an even better appreciation for developers in the ‘70s and early ‘80s) to come up with graphics that look good in such low res. My Mario character looks more like Mega Man. It is a great choice, however, because it has a low memory footprint: 504 bytes for the frame buffer. This still gives about 1.4K to work with, a gold mine.  You can get them from AdaFruit or Sparkfun for under ten dollars or on eBay from $1.88 to about $3.00.

That brings me to parts buying. If you buy them on eBay, it will likely be from an overseas vendor.  I ordered parts from several Chinese vendors and, in all but one case, I got the items within two weeks and free shipping. I would highly recommend getting them from North American vendors. If you look, you can get pricing that is close to the Chinese vendors and still get free shipping. I got my Mega and one of my UNO’s from vendors located in North America. I had those items in just a few days, so it was worth the extra dollar or two.  I also buy from AdaFruit, SparkFun and Jameco. Some things, like the UNO and Mega, cost two to three times the eBay price. I paid ten bucks for the UNO clone and AdaFruit wants $23 and JameCo had one for nearly fifty. Radio Shack sells the UNO for $34.00. As for the Chinese vendors, I bought a bunch of small parts: joysticks, Mini Pro’s, keypads, LCD panels, sensors, etc.  The smallest order was $1.88 and the biggest was $16.  In all but one case, I got the parts in about two weeks, one took a month and one never arrived, but they did issue a rebate and an apology. I would buy from them again, That was the $1.88 order.

I will post more about my project at a later date

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Real do it yourself computer using Arduino or…how to make your own game console

IMG_3043Ever since I was a kid, there were two things I’ve always wanted to build: a computer and my own video game ‘console.’ Now, I grew up in the seventies and eighties, so both of these things were pretty crude, some even crude when they were new (RCA Cosmac, I’m looking at you!) While in the intervening years, I did ‘build’ both, I cheated in doing so. With the computer, ‘building’ one was simply buying premade cards and a motherboard and installing them, hardly building one. With the video game ‘console’, I assembled a ‘pong’ style game from a kit (which I wrote about here.)

Now that I have discovered the wonderful world of microcontrollers, I can, finally, actually build both of them.mk121pal

Today’s microcontrollers are as powerful, if not more so, than yesterday’s microcomputers. For instance, the ATMega 328 is every bit as capable as the 8080, one of the mainstays in the 1970’s. Because of this, you can build real computers that are very small and require little power. They also require substantially fewer parts to work and be useful.

While I am no electronics engineer, these chips are simple enough for even someone like myself to design and build a working computer that can, subsequently, become a game console.  Companies like Adafruit, iConstrux, Spark Fun, Arduino and others all have components that are geared toward these nifty little devices. Adafruit, for example, sells the Nunchucky, which is a tiny little board that allows you to easily interface a Nintendo Wii Nunchuck controller. These controllers are, themselves, very cool and underrated. They feature accelerometers, a joystick and two buttons and are easily read by these little processors. And, with the Nunchucky, you do not need to cut its cable.

IMG_3070While it is old news, it is new news to me…the Arduino’s are capable of limited video generation and, hence, limited graphics. Now, while the graphics ability will never threaten nVIdia or AMD, they will give the aforementioned RCA Cosmac a run for its money. 

Armed with this knowledge, the Nunchuck/Nunchucky, some basic soldering skill and enough knowledge of electronics to be somewhat dangerous, I have set out to build that computer/game console.

I am actually doing two consoles: a handheld for my stepson and a somewhat more capable one as my exercise in designing and constructing said system. The handheld will utilize a small joystick, a Nokia 5110 LCD and a speaker in addition to the Mega328 Mini Pro.

Unfortunately, I ordered a great deal of my parts from eBay and just about all are shipping from China, apparently by foot as they have not all arrived.

IMG_3041However, since my Uno did arrive, I’ve been able to design and build the Half Byte game shield and start working on a prototype game, based on the Super Mario games. No, the game will not be made public, but, perhaps, a modified version with different characters may be. I do not have license to distribute any copyrighted material from Nintendo.

The game shield currently features the audio and video out connectors, the 1kohm and 470ohm resistors that allow the video to work (along with a library for the Arduino), the Nunchucky board, Arduino I/O pins and the header for the Parallax Serial LCD (which uses digital pin 2.) I may add digitized sound output as well and, perhaps, blinky LED’s and support for my custom three button controller.

arduinovideoThe tricky thing with the video is that it is all handled by the processor. The resistors ‘fool’ most televisions into ‘thinking’ there is a legit video signal. The 1k resistor handles the sync while the other handles the video itself. It was very easy to do and only involved the sacrifice of one video cable (and, since then, I acquired actual connectors so I can use better cables.)  Because the processor does all of the work, and has a very limited memory space (2k of ram, tops) the resolution is a paltry 120×96, though I had to back it down a bit to about 100×96, I needed a bit more ram. There is a common library, called TVOUT, available that most people use, though a few have written their own. The common library provides for three different fonts, lines, circles, inverse video and other niceties. It also can display bitmaps, though they MUST be correctly formatted and converting a bitmap for use is a bit of a pain. You must first resize the bitmap to fit the tiny screen, then you have to save it as a monochrome bitmap, process that file through another program that creates the hex codes that go into an array in the Arduino PROGRAM memory (NOT RAM, but the Flash memory that stores your code.) I’ll post more instructions in a later post.

proto Mario 1So, once I got the video and audio up and working, I played around with some code. First, the TVOUT demo then my own code. The TVOUT demo is pretty cool with a nice rotation sequence. It also displays the bitmap for the schematic to generate the video, an interesting inclusion.

My ‘mario’ game began as a demo. I wanted to move an image around, controlled by the Nunchuck. I wanted to use Spongebob, but I could never get him to look right in such low resolution. Now, how damned hard is it to represent a SPONGE? UGH.  Mario looked much more recognizable and that’s what I went with. Once I had my bitmaps done, moving them around was easy.  I now have Mario, a Koopa Troopa and a Warp Pipe in my level.  I am using another game called Poofy for some direction. Poofy is a side scroller for Arduino that uses some interesting methods and code that are in the public domain (and developed by the people who brought us Hackvision, an Arduino based console similar to what I am doing.)

My next step with the game is a scrolling world, Mario’s ‘weapon’ and a story.

I will be documenting the process, so stay tuned!

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