Need clever way to convert 10 bits to 8 bits

[MikeTamu]

Hello, I have a setup that I am working on for students to learn about analog to digital conversion. Basically, I have a variable voltage being converted by the onboard analog to digital convertor of a PIC16F88. This PIC has 10 bit A/D. I then want to be able to convert this 10 bit sample variable into 8 bits, and then send these 8 bits out a Port to a 'parallel in' digital to analog convertor (8 inputs for the 8 bits). Basically, I want my students to learn the limits of the PIC analog to digital conversion.

Does anyone have some clever ideas on how to convert 10 bits to 8 bits without the use of floating point variables? Simply dividing by 4 to shift the answer 2 bits works in real life, but without floating point and a limit of 16 bit variables, I am stuck.

Thanks.

[mister_e]

what about using PBP ADCIN in 8 bit results

[MikeTamu]

I assume you are referring to the 'DEFINE ADC_BITS 8' command for ADCIN?

I looked at the data sheet for the 16F88 and could not find any way to only use 8 bits for the analog to digital conversion. Does this DEFINE statement have more power than I give it credit for?

Thanks.

[languer]

When you define ADFM=0 (default) and read the ADRESH register you are in fact converting the 10-bit reading into an 8-bit reading. This is done for you by using the 'DEFINE ADC_BITS 8' command.

Hope this helps.

[Melanie]

Oh Dear, I do hope there's none of your students subscribed to this list realising that teacher hasn't a clue... that aside (I'm just poking friendly fun)... Hey Lester, I got a great money-spinning idea, we need a SUBSCRIPTION ONLY section to this website... where folks can ask embarassing questions in total privacy! Kinda like the PIC/PBP version of your local hospital's Sexual Heath clinic *laughs*... OK, OK, enough Melanie, be a good girl...

if you had MyWordVariable which contained your ten bit ADC, you could simply...

MyByteVariable=MywordVariable/4

or

MyByteVariable=MyWordVariable >> 2

both of which would divide by four happilly without the need for floats.

The best option has already been mentioned, use the PICs ADC in 8-bit mode rather than 10-bit mode.

[Acetronics2]

Hi, Mel
Hi, Tamu

A fair solution for the students coul be to use a LCD ...

Values on first line w/ 10 bits resolution ( pot position in degrees, or voltage could be more suggestive ...) , and a 8 digits bargraph ( also binary ...) on the second line ... enough room left to print the "bargraph value" ...

No, no,Thanks, no flowers ...I' ve already got here a Nobel Prize on one of these forums ...

Alain