Guru
Joined: 05/03/2018
Location: NetherlandsPosts: 5994
| Posted: 02:24pm 26 Aug 2023 |
The most accurate way to measure low frequencies (up to 20kHz) is measuring the period.
Using the picomite PIO allows for 44MHz tick (measurement resolution) at 133MHz CPUSPEED.
When measuring 50Hz you would get near 1ppm (1:1000000) resolution.
This is how it is done:
'PIO frequency counter for PICOMITE MMBasic measuring period time
'this is a PIO program
Dim a%(7)=(&h008400C5A029E020,&hE0408000A0CA0042,&h00C9008B004AA04A,&h8000A0C9,0,0,0,0)
'PIO configuration
f=133e6 '133MHz PIO execution speed
e=Pio(execctrl gp0,0,31) 'use gp0 for PIN...select the input pin
'program pio1 and start
PIO program 1,a%()
PIO init machine 1,0,f,0,e
PIO start 1,0
'pio fifo register for reading information from PIO
Dim x%(4)
'read the PIO time counted and convert to frequency
Do
PIO read 1,0,5,x%() 'read 5 count values, fifo + most recent
period = x%(4) + 4 'counts measured + instructions PIO setup time
Print f/(3*period);" Hz" 'convert counts to Hz and print
Pause 1000
Loop While Inkey$=""
end
'this is a PIO program
Dim a%(7)=(&h008400C5A029E020,&hE0408000A0CA0042,&h00C9008B004AA04A,&h8000A0C9,0,0,0,0)
'PIO configuration
f=133e6 '133MHz PIO execution speed
e=Pio(execctrl gp0,0,31) 'use gp0 for PIN...select the input pin
'program pio1 and start
PIO program 1,a%()
PIO init machine 1,0,f,0,e
PIO start 1,0
'pio fifo register for reading information from PIO
Dim x%(4)
'read the PIO time counted and convert to frequency
Do
PIO read 1,0,5,x%() 'read 5 count values, fifo + most recent
period = x%(4) + 4 'counts measured + instructions PIO setup time
Print f/(3*period);" Hz" 'convert counts to Hz and print
Pause 1000
Loop While Inkey$=""
end
In line 8 (e=Pio(execctrl gp0,0,31)) you can assign any gpio pin of the pico. e=Pio(execctrl gp26,0,31) uses gp26 (pin 31).
Success...
Volhout
P.S. if you use a picomiteVGA, you better set f=126e6 since it runs at 126MHz.
Edited 2023-08-27 00:33 by Volhout