Specifications

The above arrangement of a 4013 Dual D Type Flip Flop is set to work on a rising edge

(0 to 5 volts). Using a falling or rising edge will not affect the accuracy of the counting;

it will still see two rising edges every rotation of the motor. When the sensor rises from

0v to 5v, the flip flop is triggered and Q NOT changes from high to low which triggers

the XIRQ (active low) interrupt. Before the end of the interrupt service routine, a logic

high can be sent from PORT A to reset the flip flop and await the next rising edge from

the sensor.

This concept did not work when attached to the sensor and microcontroller. When

voltages where manually applied to the flip flop slowly it would perform successfully

however when the process was applied through the XIRQ interrupt service routine, the

logic levels would not change appropriately. The IRQ interrupt was also not working

correctly. It was initialised to recognise falling edges but would not activate on the

falling edge coming from the sensors. It would however activate if an earth wire was

touched to it. It was decided that perhaps noise or other less obvious factors were

causing this.

There seemed to be too many problems for the simplicity of this idea so it was deemed

appropriate to disregard the use of XIRQ and IRQ for this purpose. The sensor wires

were connected to the PORT G key wake up port and instantly an accurate counter was

achieved. The major issue with this arrangement was to remember not to use any

higher priority interrupts to run a routine which would turn the motors in either

direction. This would make the position of the robot an unknown factor.

As a result of this testing the odometer sensors were made successful by simply using

an Infrared LED (DSE part number Z3235) and an Infrared Receiving Diode (DSE part

number Z1956) connected to the key wake up of PORT G and the software initialised

correctly to deal with this. A simple interrupt service routine was written to add one (1)

to the counter that recorded the revolutions of the respective motor. These counter

values are then available for calculating straight line driving or even position

monitoring.