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Book 3

My third book is released! Learn what you'll need to know in order to become an embedded engineer.


Book 2

Check out my second book; learn practical stuff about building robots and control systems around Linux PCs and the Atmel AVR.


Book 1

My first book gives you all the intro you need on developing 32-bit embedded systems on a hobbyist budget.

Big box of old cellphones

TDMA Cellphones - A New Life

Cellphones, cellphones, cellphones. When the very earliest radio telephone systems went off the air in favor of more advanced technologies, it wasn't a big deal, because there were very few systems actually installed - hence not much in the way of scrap. However, in 2001 AT&T Wireless and other North American carriers began to phase out their IS-136 TDMA (D-AMPS) digital networks in favor of GSM. Contemporaneous industry reports suggest that there were as many as 93 million TDMA subscribers in the Americas at one time, and obviously all of them had at least one TDMA cellphone.

Come 2008, and the AMPS and D-AMPS networks were finally switched off here in the US - the official kill date being February 2008. Obviously, many people had already migrated to GSM or CDMA (or iDEN... chuckle), so there wasn't a massive glut of obsolete phones created on that specific day. However, the fact remains that there are millions of old TDMA phones of various vintages lying around in warehouses, repair centers and so forth. Some have been recycled, but this really means they've been stuffed in a boat and shipped to China, where some expendable labor unit has poisoned himself dissolving the gold in a pint or two of mercury. Horribly wasteful. I'm no environmentalist, but reuse before recycling is nevertheless my mantra. These phones are crammed with useful hobbyist parts - tiny motors to run the vibrate function, microphone, speaker and piezo buzzer, LCD, antenna and various other goodies.

It just so happens that I've been looking for some inexpensive LCDs for various personal projects. Cellphone LCDs would be perfect, and for the reasons explained above, I see a lot of fairly cheap TDMA phones on eBay. The problem is, nobody seems to be selling truly bulk quantities, which means I would be paying horrifying amounts of money for shipping. The LCDs are readily available from surplus vendors, but they cost around $9-$10 for a black and white LCD, and $17-$20 for a color one. Way too expensive.

To cut a long story short, I found a seller on eBay who has boatloads of ex-repair-stock trash phones, and he sold me a bunch of stripped-down TDMA phones for $2 each, including shipping, as long as I bought at least 100 pieces. The box I received - with more to come, I might add - was mostly 3320 and 3360 phones, with about 20 5120/5120i and a half-dozen 2260. The 2260, 3320, 3360 are all basically identical phones with fully interchangeable parts. The main difference is that the 2260 has spiffy blue LED backlighting, and the 33x0-series has regular green. The 33x0 does, however, have IrDA - the transceiver is easy to salvage if you want it. I explicitly asked the vendor to leave out unnecessary plastic parts, batteries, chargers and other accessories.

Unfortunately, while the Web is packed to the gills with interesting information about cellphone LCD reuse, all this information is very Eurocentric. The manufacturers of cellular telephones apparently spend their entire lives developing slightly different model numbers and variants for different markets, and (in some cases) even just for different carriers. In many cases, two identical-looking phones may have irritatingly different contents. I couldn't find anyone with documentation on the LCDs in US-market phones, and it was a real bear to work out how to use them. Hence I am writing this web page to save you the effort.

To get the easy one out of the way: The Nokia 5100 series, including the 5120, 5120i, 5160 and 6120, is apparently identical across markets, at least in the parts that matter to us. The LCD, keypad, earpiece, piezo beeper and LEDs are on a daughterboard. The easiest way to use the LCD is simply to reuse the whole daughterboard. Someone has already reverse-engineered the connections for you, and his web page on the topic is right here. These phones have an 84x48 pixel B&W graphical LCD with an NXP PCD8544 controller. It's very easy to use, and the instructions on that linked page are all you need.

The 2260/3320/3360 family are a bigger problem. They are cosmetically identical to the Euro 3310 phone, but unfortunately they are not the same, nor do they use the same LCD. In order to work out what they were doing, I soldered wires to the LCD output pins on one of the phones, and scoped them all out. Working out which pins were data and clock was easy; the harder part was sitting there with a storage scope manually decoding the transactions and guessing which controller was in the darn thing.

Here's how the LCD is mounted once you remove its subassembly from the phone:

N3320 LCD in vivo

The clear plastic key matrix is integrated with the light spreader behind the LCD. Because this is a transflective application (visible under internal or external light), the reflector on this LCD is kind of translucent. Peeling off the thin plastic membrane that holds the dome switches will also make the light-blocker behind the spreader fall out. What you do to deal with this depends on how you intend to use the LCD. If you need to use it in a backlit application, you'll need to cut off the keyboard part of the plastic - very carefully - and use a piece of sticky tape or some glue to hold the light-blocker in place.

On the other hand, you may just want to remove the LCD glass from the plastic and metal bezel entirely. The LCD is held into the bezel with a piece of very strong double-sided tape approximately in the location of the controller chip. I used a VERY THIN blade to go in through the corner of the bezel and lift it off. Avoid scratching the visible area of the front polarizer! Also note that you'll be able to see dimly through the reflector, so you'll need to put some kind of light shield behind the display.

One other point: The LCD I show here has solderable copper contacts. Unfortunately, not all of the 22xx/33xx phones will have this luxury. From observation, phones made in Brazil or Korea will have the solderable LCD. Phones made in the US or Mexico seem to have a newer LCD with glass-only contacts. You'll need to use the elastomer, and some creativity, to connect to these displays. From an electrical and software perspective, they are identical. With that in mind, here's the pinout. Note that this is a view of the BACK of the LCD, and the TOP of the display is at the BOTTOM of this image.

N3320 LCD closeup

  1. _RESET
  2. _CS
  3. Vss
  4. DATA
  5. CLOCK
  6. Vlogic
  7. Vsupply
  8. VLCD (out)
The other four pins on the connector are apparently wired only to those two capacitors you see there. The Nokia phones don't even bring these pins to the elastomeric connector. For a simple hobbyist application, run your entire circuit at 3.3V (or lower; two AA cells in series is fine). Connect the +ve supply to pins 6 and 7, with an 0.1uF capacitor to ground. Pin 8 should be connected to another 0.1uF capacitor to ground. (This pin does NOT get run to a supply voltage; it's an output from the LCD module). Data and clock lines should go to the SPI clock and data out ports of your micro, _RESET and _CS to GPIOs.

The controller is an NXP PCF8511, and the glass is again 84x48 pixels. This application has the controller chip strapped in non-extended mode (despite Philips' note that they don't recommend this), so you can't use the extended command set. The command format is a simple 9-bit word; the first bit is a data (1) or command (0) flag, and the remaining 8 bits are the command or data, MSB first. _CS must go low before you start clocking out data, and high afterwards - see the PCF8511 datasheet for details.

To initialize the LCD, first assert _RESET for at least 16us (this value taken from observing the Nokia phone) and then bring it high again. Now send the following commands, in this order (all of these have the D/_C bit 0, i.e. command mode):

0xe2 -- Soft reset
0xa0 -- MX=0
0xc0 -- MY=0
0xa4 -- DAL=0
0x2f -- HVGEN PC0, PC1 = 1
0xaf -- DON=1

I'll put up a simple demo application in C shortly - I am using the LCD with an MSP430F2012 (ez430) target board.

N3320 LCD working

And here is the final product, working happily. The comment about not being Babylonian relates to another fun project I undertook with some of the 51xx series LCDs.


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