ArcDOS Technical Description
The ArcDOS program on the Palm Organiser controls the ArcDOS hardware
The Palm communicates with a PIC18F452 microcontroller through the RS232 serial port. The microcontroller manages the I/O and battery management for the control console.
The system communicates through a bi-directional radio link between up to six display boxes. The Display boxes each have a PIC18F452 microcontroller that manages the I/O and battery management. The displays consist of three electromechanical seven-segment modules and three colour indicators made up from a matrix of 7x7 15mm octagonal electromechanical status indicators.
The Status indicators are connected in strips of seven and can be controlled by the same driver boards as the seven-segment display modules.
The Digit Driver boards are an H-bridge driver with one common pair of MOSFETs and one pair of MOSFETs for each segment. The level translation for the high side MOSFETs is performed by an optocoupler. The digit driver boards have a PIC16F628 microcontroller to manage what is displayed. The microcontroller receives a synchronous serial signal from the box controller board when a different digit is to be displayed. After an initialisation sequence the current position of the segments is known and only the segments that need to change to display the new number are actuated. The dots are the same except they only ever display two numbers (8 and blank).
The Box controller board has two switchmode power supplies on it one is 5 V for the logic and the other is 10.5V for the dots, the seven segment modules require 24V to operate. The push button power switch activates the 5V and the microcontrollers go through their initialisation routines before the digit power is applied, this is because the outputs to the H-Bridge cannot be guaranteed and cost me a few MOSFETs in early testing. The PIC18F452 controls a dual high side switch (VND830SP). During the initialisation, the audio amplifier (for the sound signal) is turned on and after a 2-second delay the main power is turned on.
The main power holds the 5V up and powers the 10.5V and the 24V to the digit driver boards. The box controller also generates a tone from the PWM output to indicate that you can let go of the button. An LED also flashes at a 1 second interval to indicate the power is on. There is a digital potentiometer DS1804 to control the volume of the sound signal.
The box controller sends an initialisation byte to the driver boards and all digits/dots are set to blank, the microcontroller then measures the battery voltage and displays the reading on the digits. The number displayed is the raw ADC (analogue to digital converter) output. The low battery values are currently set to 580 for Charge Battery Warning and 500 for shortened shut down time. The system will shut down after 1 hour of inactivity if the battery is low this time is shortened to 15 minutes.
The microcontroller in the control console scans the six pushbutton switches on the front panel and also the power switch on the back. If a button push is detected the microcontroller notifies the Palm of the request, the Palm then formats a message and sends it to the microcontroller. The message packet contains a destination so the microcontroller can determine whether to act on the message or transmit it to the display boxes. If the display boxes receive a partial message they can request a re send of the message.
If the Palm is left in the ArcDOS application when the unit is switched off, the Palm will be activated when the power is switched on again. If the Palm was not in the ArcDOS application the Palm will attempt to run the Palm HotSync application and you will need to select the menu button and then the ArcDOS icon to enter the application.