Monthly Archives: January 2011

microtouch from adafruit

Good news for those who always wanted a microtouch but didn’t have the time to build one: they are now available from the nice folks at adafruit. If you get one be sure to use the “rossum” coupon code at checkout for a 10% discount.



This version is powered by the delightful atmega32u4. It features a 320×240 pixel touchscreen, an accelerometer, full speed usb, a microsd card reader and a support for a lithium ion battery.

It has an application framework of sorts and it is possible to run a variety of applications with varying degrees of utility. Possibilites are bounded only by your imagination (and the 8 bit cpu + 2.5k of RAM). Tools support includes a PC simulator and a live sampling profiler. Code at

Building an App

Create HelloApp.cpp in apps/demos:

#include "Platform.h"

    class HelloState
        int OnEvent(Event* e)
            switch (e->Type)
                case Event::OpenApp:
            return 0;


Build, Flash and test. You should get a little app that says ‘hello’ and never quits.

Ok. What is going on here? Microtouch as an application framework of sorts that allows multiple applications to be built into the firmware. An application is ‘installed’ with the INSTALL_APP macro: the first parameter is the name that will appear in the shell, the second defines a c++ object that maintains the applications state.

The framework (Shell.cpp) sends events to the app thorugh the OnEvent method; in this example the app draws “hello” on the OpenApp event which will always be the first event an app will see. The most common events come from the touch screen: TouchDown, TouchMove and TouchUp.

Because there is only 2k of RAM in this device we really don’t have the luxury of things like memory managers. The applications state is all the heap it will ever know; its maximum size is defined by MAX_APP_BUFFER in Platform.h and is set to 768 bytes by default. If the app state is larger thanMAX_APP_BUFFER then the application won’t be visible in the ShellApp.

Lets try a slightly more complicated version:

class HelloState
        void Draw(int x, int y, int color)

        int OnEvent(Event* e)
            switch (e->Type)
                case Event::OpenApp:

                case Event::TouchDown:
                    if (e->Touch->y > 320)
                        return -1;      // Quit

                case Event::TouchMove:
            return 0;


Now we can scrawl lots of randomly colored hellos over the screen and we can even quit by touching the bottom of the screen. The Graphics.h api is fairly self explanatory: it uses 5:6:5 RGB color and supports circles, rectangles and blitting as well as text.

Stdout is connected to the USB serial port so feel free to use printf for debugging.

Sample Applications

There are a number of example applications that exercise various parts of system. They don’t all fit in the device at the same time. The APPLICATIONS path in the Makefile defines which apps get built into the firmware.


The shell is the Microtouch equivalent of the Finder or Explorer. It displays a list of installed apps and files found on the microSD card, and is responsible for lauching apps and delegating file opening to the View app. It also has code for a simple serial console:

  • ls – list files on microSD if present
  • p1/p0 – turn profiling on/off
  • lcd – dump lcd registers
  • appname – launch appname if installed


The simplest app. It turns the Microtouch off unless it is plugged into USB. The Microtouch will turn itself off after 5 minutes of inactivity so you don’t absolutely need this one, but I find it somehow comforting.


Calibrates touchscreen and stores calibration data in EEPROM. You probably will only need to run this app once if at all. Click in the red circles with a stylus until the application is satisfied with the consistency of the clicks. If you have a shattered touchscreen this app may give up after half a dozen attempts.


Displays files with inertial scrolling, currently IM2 files created with the MicrotouchTool are supported.


Exercises major hardware components including touchscreen, accelerometer, microSD and backlight.


Accelerometer demo draws XYZ values and bounces a ball depending on the orientation of the device.


Displays files with inertial scrolling, currently IM2 files created with the MicrotouchTool are supported.


The classic 3D Microtouch engine with accelerometer support. Tilt the device to move the object, touch the screen to select diffent platonic solids.


Omage to the greatest game ever written, demonstrates a technique for flicker free sprites at >60Fps.


A simple raycasting demo. Touchscreen controls speed and direction of movement. Despite the humble 8 bittyness of the CPU it manages 25fps. Play with it until you find the red wall.


Try and make all the dots the same color by touching to flip a pattern of 5. I find it bloody hard, I have only managed to complete it once. Could someone please publish a deterministic solution?


Graphics demo generates a nice infinite mesh. Looks like it is complex 3D engine with lighting, shading and geometry. It isn’t.


Click. Click. Boom.


Fingerpainting with touchscreen. Press harder for a bigger brush, select one of three brushes:

  • Cycle Chroma
  • Cycle Luminance
  • Color from accelerometer XYZ


Microtouch Tool


A simple tool to create IM2 slideshow files from jpg,png or other image files. Add as many images as you like, right click to change background, image fit or remove and image. Drag to reorder. when you are satisfied save the image to a microSD card and open from the Microtouch Shell.

Microtouch Profiler


This tool is a GUI for the built-in sampling profiler. To use:

  1. Connect Microtouch to USB
  2. Make sure the Shell is running on the Microtouch
  3. Launch MicrotouchProfiler.exe
  4. File/Open the .lss listing file that was generated when the .hex file was built
  5. Launch the target Microtouch app

The left panel displays a list of modules sorted by activity. The right panel shows the .lss file which is a mixture of source and assembly plus red bars hiliting hotspots in the code. Click on a module to move to its start in the lss file.

The built-in profiler works by sampling the PC from a timer ISR and printing it over the USB serial. If you like hexidecimal numbers you can turn the profiler on and off by typing ‘p1’ and ‘p0’ in the console.

Microtouch Simulator


A Win32 based simulator for developing Microtouch applications without the actual hardware. Simulation is pixel accurate and includes a console window that emulates usb serial stdio. The accelerometer is emulated by a series sine waves of varing period, touch pressure is selected with keys ‘1’ thru ‘9’ CPU performance is not accurately emulated.


Three OLEDs

There are a number of cheap and adorable OLED displays appearing on ebay and elsewhere. But their parallel interfaces, enigmatic driver ics and funny voltage requirements make them tricky to use. These breakout boards make it easy to connect an oled to an Arduino or any other device with a SPI interface.



All of these screens have lots of pins. Most breakout boards dutifully provide all those pins to the outside world which leads to lots of wiring up and few unused GPIO ports. Fortunately these screens can be configured to use a SPI interface saving lots of pins.

SPI has a bad rap of being slow when it comes to displays. With a bit of fiddling it is possible to get 500k pixels per second from a Arduino Duemilanove which is more than enough perf for these small screens: >30fps on 128×128.

The job of converting from 5v GPIO to 3v3 is handled by a octal buffer (74AHC244 or equivalent). They are cheap, small and a lot easier to assemble that a bunch of resistors. If you are using 3v3 IO then leave the octal buffer unstuffed and use the 3v3 holes.


OLEDs require a 12v-16v supply. Although 2 out of the 3 screens actually have ‘built in’ DC-DC converters they still need external components to generate the required voltages. These components are often fussy or inefficient and I usually just roll my own. Here I have used a FAN5331 boost converter. It isn’t expensive and because it switches at 1.6Mhz you can use a small 10uh inductor which is handy of you are cramming parts onto a small board.

The Screens

The first screen is a monochrome (actually blue) 1 bit per pixel 128×32 display based on a SSD1303 controller. These are usually $5-$8 on ebay although I have seen them in china for < $2. Because this screen is only 1bpp we can afford an actual 512 byte frame buffer on the Arduino code. Of course you don’t need to use a frame buffer if you don’t want to.

The second screen is 96×64 and has 65k colors. It is based on the SSD1332 and comes in 0.8mm and 0.7mm pin pitch versions. They are $6-$7 on ebay, < $2 in china and show up as caller id screens in lots of phones and in some small mp3 players. If you see a small color OLED with a 31 pin connector it is usually a SSD1332. This controller has hardware accelerated fills and line drawing (<1ms to fill a screen) which could save you some perf and power if you do that sort of thing.

The third screen is my absolute favorite. It is a 128×128 pixel 262k color Samsung PM12FC001B that uses a LD50T6160 controller. These show up as spares every now and then on taobao. They are found in lots of OLED digital picture frames and several Samsung YP MP3 players. The demo shows a little Wolfenstein thing running on a Arduino.

A note about the video. OLEDs don’t look very nice on video due to their use of PWM. I assure you these look much nicer in person; crisp high contrast images on all three.

Code, schematics and pcbs posted at ( The OLEDs and smartLCDs will converge into something a little more coherent in the near future.

Until next time,