Hello guys,

Does anyone knows what is the maximum sampling frequency for an analog port of a PIC uC working at 8MHz?

I am using PIC18F2550 and I want to sample a 10KHz sinewave as to calculate its average.
From the datasheet of the uC I calculated that the maximum achievable sampling rate is about 85KHz. This value is too low for my needs.

Am i correct in my calculation or I misunderstood something?

 

Not sure, but does not sound too far off to me. If you just want the average why not do that in an analog circuit?

 

My bright ideas to reduce components

 

Why is 85KHz not enough for a 10 KHz signal? anyway you have to check out the adquisition time in the datasheet at the A/D conversion requirements table. If I'm not wrong, maximum sampling frequency posible is about 130KHz.

 

I see you're using a USB PIC. I ventured there before, but got scared and went back to RS232. Have you got the USB communications working?

In table 28-29, page 400 of the most current 2550 data sheet, I'm seeing a

acquisition time of...
1.4 us

conversion time of...
11*Tad = 11(.7 us) = 7.7 us

discharge time of...
0.2 us

Total is 9.3 us. Which is 107 kHz.

 

Jut,

I won't use the USB function and I got almost the same calculations as you. However, this a very low sampling frequency to sample a 10KHz signal and obtain good results thus I will use analog components to find the average value of the 10 KHz signal.