Psion Series 5

From Inside Electronics

I bought my Psion 5 in 1997 when they first came out. I then swapped it for a Psion 5 MX in 2002 via eBay. Many more PDAs have arrived on the market in that time, but I still haven't been convinced to move away from the combination of ingenious Psion design and reliable EPOC software. Friends of mine have the iPAQ and the Palm Tungsten T3, but adding a colour screen and making it smaller hasn't made up for taking away the keyboard and reducing the battery life... Enough of my Psion banner waving, lets look inside:

The photos above show the Psion open. When the Psion is opened, the screen lifts up and tips back, while the keyboard slides forward. The centre of the screen is then over the base, so that the unit doesn't tip or move when the stylus is pressed on the screen. The keyboard uses some patented technology to keep it thin, while giving the keys a tactile feel. During fabrication a laser is used to make white patterns on the grey keys - so the keys are placed on the keyboard blank and then the symbols are 'burnt' onto them, leaving a mark that cannot be scratched off. The plastic under the keyboard is silvered to reduce electromagnetic interference.

The photos below show the Psion closed. In the middle photo the plastic case over the screen has been removed. The plastic case of the Psion 5 has a rubber finish so that it cannot be easily scratched. Unfortunately this rubber can wear off, and so the Psion 5 MX has a plastic finish with a matt metallic colour to hide any scratches. More modern devices, such as digital cameras, use thin metal cases with a matt finish. It is worth pointing out that the metal badge in the left photo is slightly raised, so that it rests against the battery compartment when open and saves the plastic case from being marked.

The middle photo above shows the thin backlight, using technology made famous by the Indigo backlight for watches. This is only needed in dim lighting and the LCD screen on its own allows for a much longer battery life than TFT screens (30 continuous hours or so). The right hand photo shows the back of the LCD screen, with a resolution of 640 by 240 (half of a VGA screen). In front of this is a touch sensitive membrane to allow writing and selecting on the screen with the stylus. This uses a scratch resistant plastic, so that when a pen is accidentally used it does not leave a mark.

The screen and touch sensitive membrane are shown in the left photo below. They share the same ribbon cable to the main board. This ribbon is the Achilles heel of the Psion 5 as is the first thing to wear out, but PsionFlexi can replace a broken ribbon cable with an improved version for a reasonable fee. The middle photo shows the underside of the keyboard, with the compatibility logos: European certificate, Compact flash, IrDA Infra-red, EPOC operating system, ARM Processor and of course - made in the UK. The right hand photo shows the battery compartment, which holds two AA batteries. These have a high power to size ratio and are also cheap. I don't use rechargeable batteries as Alkaline batteries last longer and they only need replacing once a month.

The photos below show the Psion from underneath. The left photo shows the Psion in the open position, with the keyboard out. The Compact flash disc drive cover is on the left, with the dictation and playback buttons at the bottom. These three buttons can also be used to snooze alarms or reminders. The stylus is stored in a slot above the disc drive, with a positive latching action to stop it falling out. The backup battery compartment is to the right, which also contains the reset hole. The battery can be removed using the stylus, thanks to a slot designed for this purpose. Under the battery there are six contact points that are used at the factory to program the Psion. The Psion 5 is sold in many countries, but the only difference is the software programmed into the ROM through this port, and the symbols burnt onto the keys by the laser.

The middle photo shows the one and only circuit board, with the disc, stylus and backup battery in place. In the right hand photo these have been removed, along with the battery compartment cover. The ribbon cable to the speaker can be seen in the top left and the microphone in the bottom left. In the top right is the infra-red port and serial port, with the power connector for the DC supply. The module in the centre of the board holds the EPOC operating system in ROM, with the ARM processor in the Cirrus chip underneath.

The circuitry to the left of the backup battery is the power supply, with an inductor to step up the voltage. This is the part that 'whines' when the processor or backlight are drawing power. The circuit pulses 3 volts from the batteries to the inductor, and then uses the back EMF to catch the higher 5 volts required for circuit, backlight and Compact flash disc, with around 95% efficiency. The ribbon cable to the backlight can be seen in the bottom right. There is also a trimming capacitor for the clock, which is set at the factory. This reduces the drift in time keeping and allows the Psion to be reasonably accurate.

The left hand photo below shows the shell with the circuit board removed. The grove used to guide the keyboard can be seen in the middle. The plastic is silvered again to reduce electromagnetic interference. The middle photo shows the circuit board in the bottom of the case, and the circuit board is shown on its own, turned round, in the right hand photo.

On this side of the circuit board the battery connector and memory can be seen. There is a switch to detect when the disc drive door is open. The door is marked with a serial number, which is also programmed into the Psion. The switch in the centre detects when the keyboard slides out, so that the power can be turned on and off when the Psion is opened and closed. There are lots of other good websites with photos from inside the Psion 5 - follow the links below.