An 8-bit microcontroller was chosen to process the output
signal produced by the amplification stage. The Microchip PIC16F877A was
selected due to its additional output and processing power, and also its
onboard 10-bit analogue to digital converter and in-circuit debugging features.
Using this highly integrated microcontroller allowed for a simpler design and
trouble shooting debugging process. Due to the use of a microcontroller to
calculate the beats per minute (BPM), it was decided that a liquid crystal
display (LCD) module would be the most flexible way of displaying this
numerical output. It was originally planned that several seven segment displays
could be used, but again it was deemed worthwhile to integrate the display unit
together and limit the number of components required. In addition, the information
which the LCD could convey was greater. Below is a block diagram of the
microcontroller and LCD process:
Regarding the actual BPM calculation (assuming that it was
possible to translate each R part (the blip/spike peak) into singular events
occurring in a timely fashion of course) it was originally going to be done by
measuring the total number of spikes within a certain amount of time and then multiplying
this count by a factor (as it is done when using a clock and your hand). With
the use of the microcontroller however more precise measurements were able to
be made resulting in an output of greater accuracy and speed.
