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Forum Index : Microcontroller and PC projects : Picomite/PicoMiteVGA V5.07.05 release candidates
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| Volhout Guru  Joined: 05/03/2018 Location: NetherlandsPosts: 3503 |
Dear PLuto, Not sure about you, but I do not have a good feeling about the frequency measurement results (Setpin x,FIN). The readout (also in lower frequencies) is not accurate. Like it is missing counts. I will dive into it a bit deeper, but the combination with PWM and FIN counting inputs does not work as I thought. I wanted to see exact numbers. Here are some results PWM FIN FREQ SCOPE FREQ 20000 20000 20000 50000 50000 50000 80000 80020 80030 100000 99000/99950/99991 100000 200000 198000 Every time I run the program, PWM at 100kHz, the reading is different (more or less consistent), but different. I hope my text is clear. When I restart the program, the reading can be 99940 and stay around that value for minutes. Stop the program, restart, and the value can be 99000, and that value remains similar over minutes. 100000 99991 100000 99988 100000 99988 100000 99991 100000 99991 100000 99988 100000 99991 100000 99991 100000 99988 100000 99991 100000 99991 100000 99990 100000 99988 100000 99991 100000 99991 100000 99988 100000 99991 100000 99991 100000 99988 100000 99991 100000 99991 100000 99991 100000 99988 100000 99991 100000 99991 100000 99988 100000 99991 100000 99991 100000 99991 100000 99988 100000 99991 100000 99991 100000 99988 100000 99991 100000 99991 Based on these measurements I can only conclude the frequency counter can be used up to 50kHz. Volhout Edited 2022-12-07 05:24 by Volhout PicomiteVGA PETSCII ROBOTS |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 8572 |
At 378MHz the PWM clock is running at 189MHz which means at c1Mhz there are only 189 clock pulses. The next value down would then be 190 clocks = 994.7 KHz and the next up 1.005MHz. At fast PWM speeds this is the limit of the pulse accuracy and the duty cycle is also affected in the same way |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 3503 |
Hi Peter, I am running 126MHz for above test. I am using the FIN function with a gate time of 1 second. I would expect it to count 1000000 pulses. Are you measuring pulse width in the FIN mode and converting it to a frequency ? EDIT: oh...the PWM is not accurate ? But I am measuring it with a scope to be stable (at least at 100kHz the scope frequency counter says 100.0kHz) setpin gp0,pwm setpin gp9,fin dim integer n=100000, m pwm 0,n,50 do m=pin(gp9) pause 2000 print n,m 'inc n,10000 loop OPTION SYSTEM SPI GP18,GP19,GP16 OPTION SYSTEM I2C GP14,GP15 OPTION AUTORUN ON OPTION COLOURCODE ON OPTION DISPLAY 40, 100 OPTION LCDPANEL ILI9341, LANDSCAPE,GP20,GP21,GP22 OPTION SDCARD GP17 OPTION AUDIO GP6,GP7, ON PWM CHANNEL 3 OPTION RTC AUTO ENABLE another run of the same program > Time taken: 1752mS RUN 100000 0 100000 99000 100000 99000 100000 99000 100000 99000 100000 99000 100000 99000 100000 99000 100000 99000 100000 99000 Volhout Edited 2022-12-07 05:40 by Volhout PicomiteVGA PETSCII ROBOTS |
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| Pluto Guru Joined: 09/06/2017 Location: FinlandPosts: 329 |
When I made the measurements, I found that outputting sine or triangular wawe the measurements were more accurate than with square wawe. Square wawe frequently gave double frequency on the Pico. Maybe I should have had some kind of attenuator or terminating resistor on the signal generator output? I did also see fluctuations in the lowest numbers of the frequeny, but I tought it was due to my hobby level set-up. When I measured with the PIO program about the same error-% was obtained. Again I thougt it was the contribution from my test set-up. |
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| Pluto Guru Joined: 09/06/2017 Location: FinlandPosts: 329 |
Made new shielded connections and measured the performance of the PIO frequency meter again. With 2MHz input (now confirmed by oscilloscope) the measured value is on average 296Hz too low and the standard deviation 29Hz. The error increases with increasing frequency. At 4MHz it is about 370Hz too low with a sd of about 120Hz. At 500kHz the measuement is about 1Hz too high with a sd of about 1.5Hz. The measurements were averaging 100000 measurements (ca 6s per mesurement). |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 3503 |
Hi Pluto, My observation is on the build in frequency counter function, not the pio counter. The build in function works less accurate than the function in the MX170. That was unexpected. Volhout. PicomiteVGA PETSCII ROBOTS |
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Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1593 |
Sorry wrong thread. Bill Edited 2022-12-22 14:31 by Turbo46 Keep safe. Live long and prosper. |
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