Author Archives: rossumblog

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,


A Smarter Display

Connecting display to Arduino can be expensive, complicated and unsatisfying. The smartlcd attempts to make it cheaper, simpler and more fun.
There are lots of interesting displays hiding in cell phones, cameras, mp3 players and various other devices. In this post we will be looking at two of my non-Nokia favorites: The iPod Nano 2G display and the so called “cheapest TFT in the world”. Then we will be making a gadget that hopefully does something useful with them.

To repurpose a display we need to determine its interface mode (serial/parallel), pinout and driver ic. If the display has a nice part number printed on the side then you might get lucky and have the interwebs answer all your questions. Much more often than not you have to do it the hard way.

Count the number of pins on the connector. If there are 8-16 pins it is almost certainly a 8 or 9 bit spi interface. Find the LED supply pins (almost always the thickest traces on the flex) and give them the respect their elevated voltages deserve. Attach a logic analyzer to a live system determine the spi clk (wiggles most), the spi mosi (wiggles second most), the spi select and the reset (wiggles once). See this example.

If you have 20 or more pins you have an 8 bit parallel interface. If you have 24 or more chances are it is 16 bit parallel. Many displays have the ability to run in both serial and parallel modes that can be selected with one or more external pins. If you are short of GPIOs this is a good option.

iPod Nano 2G
The iPod Nano 2G has a lovely little 22 pin transflective 176×132 screen. It has a 0.3mm pitch connector as seen in the iFixit tear-down. Nearly all 0.3mm ffc connectors have an odd number of pins. Apple thought different and used a DDK FF12 that is very hard to come by. After buying lots of replacement LCDs ($5 ebay + many $1 auction wins) and lots of dead/dying nano2Gs it was time bust out the fine transformer winding wire and a logic analyzer.

The data bus is easy to find: look for 8 consecutive bits that change all at the same time. The WR, CS and CD signals are then fairly easy to spot based on decreasing activity. As it turns out there are at least two different driver ics in these screens: A narrow one that looks a lot like a ILI9163 (8 bit wide commands, sets up blits with 0x2C) and wide one that looks a lot like an ILI9320 (16 bit commands, sets up blits with 0x22).

Although these controllers are similar to documented controllers they still have major differences and I needed to record an initialization sequence from a live boot in order to get them to work.

Connector pinout Nano 2G
        1        LED+ 6V
        2        LED-
        3        Frame Marker
        4        GND
        5        D7
        6        D6
        7        D5
        8        D4
        9        D3
        10        D2
        11        D1
        12        D0
        13        RD        Read
        14        WR        Write
        15        CD        Command/Data
        16        CS        Chip Select
        17        Reset
        18        GND
        19        VIO        3V3
        20        VDD        3V0
        21        ID0 
        22        ID1
Preview of an upcoming project using iPod Nano 2G screens:
The TFT 20
If one dismembers enough mp3 players one starts to notice patterns of part usage. One display caught my eye: it was very common in cheap 128×160 mp3 players, was a crisp and high contrast TFT, and had a hot bar solder connector that looked like it could be soldered by humans.

After dismembering a very nice Insignia digital photo keyframe and applying the logic analyzer the traces look very familiar. It was a ILI9163. Other devices turned up a ILI9161 and a Samsung S6D0144. All variants seem to have a very similar physical outline; another defacto standard like the touchscreen used in microtouch.They are widely available in China for $2 making them the cheapest TFT going.

So how can we make this lovely little screen useful to say an Arduino enthusiast? It needs 3v3 io on 14 pins connected to a 1mm pitch hot bar solder connector, a 6v boost converter to supply the leds, drivers, apis etc to make it useful. Not the simplest thing to do on a breadboard.
Thats where smartlcd comes in.

The smartlcd adds intelligence to a TFT 20 display. An inexpensive Arm Cortex M0 or M3 microcontroller is used to provide graphics and media processing as well as providing a high speed serial interface the 3v3 display. With additional components the smartlcd can offer a spi-flash or microSD file system and usb. One single pcb scales from bare bones serial through to a stand alone lipo battery powered device.
A minimal configuration with just the backlight boost converter and serial interface:


smartlcd uses a serial link to connect to Arduino and other devices The serial link runs a slip framed, software flow controlled RPC at 1MBit. 5v to 3v3 level conversion is not necessary; the smartlcd inputs are 5v tolerant and can plug directly into the Arduino RX and TX pins. Because it is connected to the serial interface, the smartlcd can reprogram the Arduino and under the right circumstances the Arduino can be reprogram the smartlcd. The smartlcd can also be configured to be reprogrammed via USB and you don’t have to know anything about arm or own a arm development kit to build one.


The client does not have to be a Arduino; the smartlcd can connect to virtually any serial device or USB. However smartlcd makes it very easy to display text, graph values and draw graphics quickly on Arduino:
// Console demo
        int a[2];
        a[0] = analogRead(A0);
        a[1] = analogRead(A1);
        if (_mode == 0)
                Console.Write("X:%d Y:%dn",a[0],a[1]);

        // Circle demo
        int x = random(128);
        int y = random(160);
        int r = random(70);
        int c = random(0xFFFFL);

Fully loaded versions of smartlcd can decode JPEG, PNG and will be able to decode some forms of video. Source code, schematics and Eagle files:

Until next time


Building the RBox.

I finally got around to assembling a stand alone version of the RBox. As some of you correctly noted building a videogame for the price of a latte that depends on a $30 dev kit is cheating a bit. This version is self contained and while not practical or useful it is at least fun to build.

The design sandwiches a lithium button cell between the psp joystick and the pcb. It adds a single button that serves as both the power switch and a fire button. 2 axis control + fire may seem a modest level of input but modern standards but if it was good enough for Atari is is good enough for me.

Thin bendy metal on top of the cpu and on the bottom of the joystick provide a suprisingly effective friction fit for the CR1632 battery. Don’t try to solder directly to the metal on the bottom of the joystick. When running a game and playing audio the device uses about 28ma so I get about 4 hours of continuous use from the CR1632. Feel free to use a CR1616 or CR1620 for a slimmer look and more frequent battery replacement. 

The schematic is virtually identical to the prototype with a few exceptions. The joystick VCC line is connected to a GPIO rather than  VCC to reduce power during normal operation and especially during deep power down. The fire button is connected to the WAKEUP pin that brings the beast back from deep power down. The code will deep power down the RBox after 3 minutes of inactivity. While turned off the RBox uses about ~200na as far as I can measure on my crappy meter. The board supports both composite and s-video.

If you don’t feel like making your own pcb order them from This is simply the cheapest and best way of getting pcbs in small volume. Nobody else comes close. Unless you really like what ferric chloride does for your sneakers there is no reason not to use these guys.

New code, schematic and pcb posted on If you would like a kit post a comment and if there is lots of interest I will see if I can get one organized.

Until next time

Screen Play: Lots of other screens for microcontrollers.

If you enjoy LCDs and microcontrollers chances are that you have tinkered with the ubiquitous Nokia 6100 screen. I love the fact that a youtube search for “Nokia 6100” produces may more AVR and PIC hacks than phones. In a bit of a departure from my normal projects this is the first in a series of posts on lots of other little known display choices that are better, cheaper and just more fun.

Despite its popularity the Nokia 6100 display has a few problems:

  1. Small (132×132)
  2. It is a CSTN (passive matrix) display leading to ghosting if things move quicky. Koopas are especially lethal if nearly invisible.
  3. Limited color depth of 12 bits (4096 colors + dithering on some displays).
  4. It comes with 2 incompatible driver ics (Philips or Epson).
  5. Not cheap: $15 from sparkfun or (gasp) $35-$42 for breakout boards.
  6. A fiddly, relatively uncommon 0.5mm connector that tends to tear off expensive breakout boards rendering them useless.
  7. Needs 6V for the backlight (2 leds in series).

The Nokia 6100 first shipped in 2002. Of the hundreds of models of phones from nokia (yes, hundreds) surely there are other screens of interest? A quick check in my junk phone archive of hundres of phones (yes, hundreds) turned up a few interesting candidates.

A quick check of the schematics turned up a series of SPI driven displays connected to 10, 22 and 24 sockets.

Nokia 1600: Although the 1600 screen uses the same 10 pin connector (Hirose DF23-10DS) as the Nokia 6100 the pinout is very different – so different in fact that if you plug a 1600 screen into a 6100 phone blue smoke will be emmitted and your phone will become a purely decorative item. The screen is speced as 96×65 CSTN.

Nokia 6101: Two displays here. A 96×65 CSTN caller id screen with backlight leds on the phone pcb (fail/win) and nice big one with a 22 pin 0.5mm connector (Hirose DF23-22DS) that is a 132×162 TFT (acvtive matrix) display.

Nokia 2760: Two displays again: an oh-so-cute teeny 96×65 blue monochrome display with the 10 pin connector and a 132×162 TFT with a 24 pin 0.4mm connector. These are not the Hirose DF30 series; I am still looking for a definitive source.

We know they are SPI, so lets get them wired up to a logic analyser and see if we can identify what controller they use. Once wired up we record the traffic going two and from the LCD as the phone boots. Looking at the traces it is clear that all these phone used a fairly uncommon 3 wire mode of SPI to determine what display is attached.

After an initial 0x11 (Sleep Out) 9 bit SPI command the 0xDA,0xDB and 0xDC (Read Device ID) commands are followed by 8 extra clocks during which the MOSI line is driven by the LCD. In this 3-wire SPI mode the MISO is really SISO (slave in slave out) and is usually not supported by hardware so we will need to bitbang during this discovery phase. This is the way Nokia 6100 phones can tell the difference between the Epson controller (that does not respond to RDDID) and the Philips controller (that does).


Looking at SPI recordings reveal that the controller on the large screen looks an awful lot like the Philips PCF8833 controller in the 6100. Searching by RDDID manufacturer id 38H turns up the Orise SPFD54124B for the 6101 screen. It has a lovely 262k frame buffer and supports a 12,16 or 18 bit color format. Ironically googling this controller led to a great site that details this and other earlier phone displays. The caller id screen seems to be a SED1565 or similar, the 1600 seems similar to the Philips.

The 22 and 24 pin displays support SPI or an 8 bit paralell interface selected by a p/s pin. SPI is usually fast enough for smaller screens unless you are really perf sensitive. SPI means fewer pins on the mcu, fewer lines you need to convert from 5v to 3.3v etc.

Now the really good news. The 6101 displays are really cheap on ebay. <$3 with free shipping much of the time. They address problems 1) thru 5) listed above. The 1600 screens are also cheap if you need something small – dealextreme has them for <$5. 1200 displays are pin and code compatible with the caller id screen an very low power if you don’t use a backlight.

All these and more in action:

The breakout board above supports both 10pin pinouts as well as 22 0.5mm and 24 0.4mm pinouts. It has a built-in boost converter for generating various led supply voltages controlled by pwm from the mcu. It has a sense pin to allow you to measure the backlight current and adjust it accordingly by varying pwm duty cycle.

Download this file

The software in the demo detects when a display is attached, selects the right driver and runs an appropriate graphics app: Wireframe 3D for mono screens, the reference Rossum icosohedron and a raycast lattice for color. As always code and schematics/pcbs will be posted on Sourceforge.

In the next post, I will look at displays from several non-Nokia phones, the worlds cheapest TFT and the Ipod Nano 2G.

Until then



UPDATE: PCB, schematics and code for AVR and NXP posted at




RBox: A diy 32 bit game console for the price of a latte

Uses the smallest and cheapest 32 bit CPU to generate 3D graphics and sound.

The RBox is a game console that is simple enough to build on the prototype area of a dev kit; no pcb required just a crystal, a few capacitors and resistors.



320×240 composite or s-video output generated entirely in software
256 colors with standard palette, up to 8k colors
8 bit 15khz stereo audio
~$1 Analog joystick
~$1 CPU

A bit of history…
Ever since the Atari VCS generated video by Racing the Beam i have wanted to build something that generates video on the fly. There have been lots of great diy examples of this in the intervening years (Rickard Gunee’s Picpong and SX Tetris, the lovely Uzebox) but the arrival of the ARM Cortex M0 parts from NXP rekindled my interest. The NXP LPC111X family is smallest 32 bit CPU. It is an ARM Cortex M0, the same device I used in the Wikipedia reader. This family of devices starts at under $1.

The LPC111X parts have ample horsepower for black and white video, as many less powerful chips have done in the past. At a max clockspeed of 48mhz they require 2 clocks to access memory or gpio so you could write a blit loop fast enough for 320 horizontal resolution (each pixel at 320×240 takes 8 cpu clocks, enough time for read/palette lookup/write/test/loop). Add a couple of resistors for a DAC, add sync pulses and you are in business. Overclock to 57.27272 and then you are a multiple of the chroma carrier and can generate colorburst and manipulate chroma phase: Now I had nice color bars but it wasn’t clear how generalize this to a practical system that could be programmed to generate interesting and useful images.

The real breakthrough came when I realized I could re purpose SPI to manipulate chroma phase while the cpu used gpio to write luma. SPI also has a 16 byte fifo on these parts which allowed chroma writes to be queued relieving pressure on the luma timing. With SPI emitting bits at 1/2 the cpu clock rate I could get 8 bits per chroma clock, enough to do 8 different phases for 8 different hues. All the other 248 combinations of those bits generated other hues and levels of saturation, suggesting a palette of some sort might be useful.

Color generation solved, now I needed graphics. A frame buffer was out of the question: at 8 bits a 320×240 frame buffer is 75k. These devices have 2k to 8k total memory so another approach is needed. After fiddling with tiles (as in Uzebox) I eventually settled on a line buffer approach where the application sends individual lines to the video driver for display, allowing code that looks and feels like it is working with a framebuffer without the actual memory.

There are 2 pixel formats supported: 5 bits of luma with 3 bits of chroma index or 4 bits of luma with a 4 bit chroma index. The chroma indexes map to the actual 8 bit value emitted by SPI. The chroma palette can be changed every line allowing up to 8k colors on the screen at the same time. With 8 bit color filling the line buffer is simply a matter of dealing with 1 byte per pixel blitting and things like smooth scrolling become very simple.

The video driver generates 3 interrupts per line: i0 at start of the line to pull hsync and emit an audio sample. 1 pcm sample gets emitted per channel per scanline at 15.7khz which is the line rate of ntsc. i1 happens at the end of hsync. The driver releases hsync and feeds the colorburst data into the SPI fifo then returns. The active video interrupt i2 actually emits the pixels and uses about 70% of the cpu.
Much as I love this CPU there were a few wrinkles. At this clockspeed, it needs 3 wait states to access flash. If you execute code from flash on this part you can never be sure when those wait states will slow you down: the same code may run at different speeds depending on its position in flash. Really bad if you are writing a blit loop that has really tight timing requirements like generating ntsc in software. The solution was to copy the critical routines to RAM where they run without any wait states.

Other devices like the Cortex M3 based LPC13XX and the LPC17XX have flash accelerators and single clock gpio writes. The LPC17XX also has DMA that makes all this sort of thing really easy – 640×480 component video should be possible. Although more expensive than the M0 parts, they are still ridiculously cheap.

About the demo video

Scrolling around a 8192×2048 map of a certain hedgehogs homeworld. The demo uses the analog joystick as input, features single pixel horizontal and vertical smooth scrolling and runs at at 60fps. The audio in the background (the music, not the leafblower) is coming from the device.


500 particles spraying at random from two sources over an animated background. The texture in the back is being generated every line by multiplying the luminance of a blob pattern by sin(y). Single cycle multiplies take a lot of getting used to; it is often faster to multiply than to use shift/add “optimizations”. 60fps.

Platonic solids float over an animated 3D plane with weird patterns in the sky that gratuitously change color. The 3D models are rendered scanline by scanline and composited with the dynamically generated backgound. Once again, because we don’t have a frame buffer, we get 60fps with no tearing.
How to build

If you want to make your own I have included the schematic and the code. I built the prototype on a LPCXpresso devkit available at Digikey, you will need to replace the stock 12mhz with a very common 14.318mhz crystal.  I bought a reel of these so if you can’t find one I will send you one. The analog joystick is a replacement part from a PSP. $1ish on ebay. The wiring photos are a little tricky to follow, check the schematics for a clearer version.

Source for the LPCXpresso/Eclipse project is posted on

I will be doing a PCB version so for those squeamish about little green wires can hang on ’till then.

until next time,


Wikipedia Homebrew device features Cortex M0 processor, all human knowledge.

Gotta love Wikipedia. Gotta love really cheap, powerful Microcontrollers. They are even more delightful when combined.

This is a prototype of a cheap offline wikipedia reader based on a new NXP ARM Cortex M0 microcontroller. It renders offline dumps of Wikipedia or other text formats (books, html etc) with a simple touch interface. The dumps are stored on a microSD card and are rendered on a inexpensive touchscreen LCD. I will publish full schematics, PCB layout and source code to a final handheld version that looks an awful lot like the Microtouch.

The Software

An offline grinder tool converts xml dumps from wikipedia and other sources into a compressed text layout format that is digestible on a small device. The hard part is decompressing and drawing the text with few cycles and very little RAM fast enough for it to feel like a responsive little consumer electronics device rather than a lumbering PC. The keys to this turned out to be a spatial index that allowed fast rendering of segments of a page and hugely simplified compression. The text renderer uses subpixel positioning to help make teeny fonts readable without slowing down drawing.

The Hardware

NXP are onto something good with these ARM Cortex microcontrollers. The are cheap in onesies (<$2), fast (50Mhz), have plenty of memory (32K flash, 8K sram) and have a really nice dev kit (LPCXpresso) with Eclipse based tools and delightful Serial Wire Debug. Hardware breakpoints. 12K gates. Bloody amazing.

This project uses the LPC1114 Cortex M0 but the PCB will also take a LPC13XX Cortex M3 part that is faster (72Mhz) and has full speed usb. The prototype uses a LPCXpresso kit with lots ‘o jumpers and a ILI9325 based LCD, the same as the Microtouch.

What about the AVR?

As it turns out, this also runs just fine on the AVR based Microtouch classic hardware. It isn’t quite as zippy but still works well. The code isn’t really optimized yet and there is probably room for improvement on both platfotms. You might expect the Cortex M0 version running at 48Mhz to be 4 times as fast. It isn’t. The M0 always requires 2 clocks to read or write GPIO (unlike a single clock for the AVR) so the LCD blit loops are at best twice as fast. Code size is about the same as one might expect.

For those of you who have built your own Microtouch device I will make sure the classic hardware is fully supported. For those of you who have not built their own Microtouch yet I hear that there might be a kit in the works. Watch this space.

Until next time,


Code and schematics posted at


Teeny AVR Media Thing – the Nanotouch

How small can something get and still be useful? This little experiment uses a 96×64 OLED display with a click screen interface that may not be useful, but at least its fun.

Like the last project, this uses an 8 bit AVR. This time it is a Atmega32u4 that is cheaper and smaller than the Atmega644p used in the last project and has 32k flash, 2.5k RAM and full speed USB in hardware.

The screen itself is a beautiful little thing that uses a SSD1332 controller. These can be found on ebay, I have also seen them in China for $2. They are fragile – if you build one of these yourself you might want to buy a few spare screens or wait until I redesign the board so it does not need to flex as much.

The screen sits on 4 tact switches that provide input to the user interface. Movies and UI transitions are streamed from a microSD card.

The 3D demos are an homage to the brilliant yoomp  and of course to John Carmak for establishing the whole first person shooter cultural phenomenon.

Schematics, PCB and source code on Sourceforge at