Specifications

38
provide inverters. The logic signal from the sensors was then applied through these
joined inputs and the output provided an inverted signal of the input.
The program code simply checks the status of each sensor in a loop by loading PORT A
into an accumulator and performing logic decisions on the value loaded. The
microcontroller now reads a logic one for an activated signal and a logic zero for a non-
activated sensor. Hence, if all sensors are activated the register will read 00000111 or if
no sensors are activated it will read 00000000.
To summarise the distance sensors used on the Mobile Manoeuvring Robot the
following points can be observed.
•
Infrared LED’s (DSE part number Z3235) clocked at a 38 kHz square wave with
an even mark to space ratio are used for the transmission of the sensors light.
•
Buffered Infrared receiver chips (DSE part number Z1955) with the
recommended filtering and bypassing are used to pick up the transmitted light.
•
Extra IR LED’s with variable brightness are used to saturate the IR receivers to
ensure successful performance
•
The logic outputs of the sensors are inverted to communicate effectively with
the Motorola HC12
•
Sensor status is read in by the microcontroller as data on PORT A.
In retrospect to designing custom IR sensors for the simple use of obstacle detection, it
would be far more practical to spend the money on tuned sensors that work without
error. The robots sensors work reliably now; however an enormous amount of time was
spent on designing these which would have been more effectively used on the objective
and practicality side of the design.