The original Pilot was launched by US Robotics in 1996, the second model became the Palm Pilot. All subsequent models were just called Palm. 3Com acquired US Robotics, and the Palm V was launched in 1999.
Clearly a forerunner of todays tablets, Palms were very popular. The Palm V featured a 16MHz CPU, 2M RAM, 3.2″ 160 x 160 pixel LCD and a touchscreen together with infra-red and RS-232 connectivity.
Do you remember the Graffiti shorthand character input language that was used to do handwriting recognition? I can recall becoming pretty proficient in it at one point. My Palm actually replacing my lab notebook and for taking meeting notes.
Getting into this thing is not easy. Heat gun and a lot of force is required to separate the front and back panels, which are glued to a plastic frame.
Just look at the amount of glue residue on the back panel. You need to do this even to just change the battery?! You have to be pretty lucky (Or possess skills I don’t have) to get this apart and back together without breaking it. Fortunately this one isn’t going back together!
With the panels off it just required the battery to be disconnected, there are three connectors to unclip and then the thing can be pulled apart.
- Sipex SP385 RS232 Line driver/receiver
- Samsung KM416V1204CT 1M x 16bit DRAM
- Fujitsu 29LV160B 16Mb Flash memory
- Linear LTDT (? probably a voltage regulator – confirmed after depot)
- Sipex 4422 Electroluminescent lamp driver
- Motorola DragonBall EZ 16MHz CPU
- Burr Brown ADS7843E 4-wire touchscreen controller
The large die labeled CHB-03F is not an IC it is actually a noise maker/beeper. Alongside the CPU is a 32.768kHz crystal oscillator (FSR327), and beside that the round device is a wound wire inductor which is a little unusual to see – I figured out it is part of the back light circuit which I will look at more closely.
The rear of the board contains the input buttons and a bunch of passives, mostly resistors. If you look closely you can see a few of zero ohm resistors. They probe out as shorts. They might be there as jumpers but looking at the board layout I think they were put there so that during evaluation they could be removed and a meter used to measure power to various circuits.
For the silicon lets take a look at the display and the touchscreen.
The Palm V uses a 4 wire resistive touchscreen. For most applications today these have been replaced by more accurate capacitive touchscreen. They are still found in low end applications such as point of use terminals.
From the front of the screen you can see the four terminals (top. bottom, left and right) printed to the back of the glass together with a green insulator.
From the rear of the screen you can see 6 connections poking through the green insulation that bring the horizontal connections through to the plastic layer that has metal strips on either side. On both the glass and the plastic film there is a thin film of Indium Tin Oxide (~20nm) that has been sputtered onto the surface. Indium Tin Oxide is interesting stuff as it is one of very few conducting materials that is also transparent making it very useful in screen applications. From both top to bottom connections, and across the plastic film, I measured exactly 500Ω. Indicating a tight control of the ITO deposition process. A small air gap (Set by the green insulator) separates the two conducting ITO films. Where the stylus touches the screen, the ITO films touch, and the location of the stylus can be triangulated by the resistance between the four electrodes.
Glued to the back of the plastic/ITO film is a plastic film, contain a silver green printed area where the alpha-numeric entries are made.
This is what it looks like under the microscope. The silver/green area looks like a bed of small emeralds! No idea what this is but pretty cool to look at.
The four terminals connect into the Burr Brown ADS7843 Touchscreen Controller. The ADS7843 is still an active production part on Texas Instruments website. Finding a 20 year old ic still in production is pretty rare.
Peeking into the logic area I can see that for a 1999 analog part this uses a pretty advanced process. The gates are at the limits of resolution in my optical microscope, but I can approximately measure them as smaller than 1 μm so I think this is made on a 0.8μm process with 3 metal layers.
The ADS7843 datasheet describes it as a 12-bit sampling Analog-to-Digital Converter (ADC) with a synchronous serial interface and low on-resistance switches for driving touch screens. Here is the block diagram
The most obvious feature of the die is the capacitor array. That is an array of individually switched binary weighted capacitors that make a sample/hold capacitive DAC that is used to and compare with input voltage in a Successive Approximation ADC
There is a lot of interesting silicon used in the Palm V. In Part 2 I will look at the LCD display driver, the backlight controller die and the voltage regulator.