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Forum Index : Microcontroller and PC projects : STM32F407 verses APM32F4 (Chinese clone)
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poida Guru  Joined: 02/02/2017 Location: AustraliaPosts: 1418 |
looking at the STM32F407VGT based Black boards, some ALiexpress vendors offer STM32 chips or GeeHy APM32 chips. Supposed to be interchangeable. there are differences. One thing I have found is the ADC . I tested it using my FFT code (with options for FFT size, sample rate etc.) No changes were made to the code loaded into both boards. I used the Arduino IDE with STM's support package for it. test condition is sample rate: 500kHz sample size: 2048 ADC resolution: 12 bits Flat top window time average: 8 traces (smooths out the noise) 20 db/vertical division 1V p/p 60kHz sine Blue trace is a sync pulse for the DSO trigger Yellow is the FFT magnitude. 0 to 250kHz over 12 divisions First is the STM32F407  then the APM32F407  It is clear the APM32 has an inferior ADC design. The second harmonic of the 60kHz is -42db The APM chip also has another harmonic at -60db The STM chip has nothing above the noise level but this is a few db more than the APM uC I have tested this at various sample rates from 500Hz to 500kHz and that 2nd harmonic is always there, no matter the signal frequency. The aliexpress vendor has the APM board only about $2 cheaper than the $15 STM based board. There could be more differences in the chip but this is the first one I found so far. here is the code I used if anyone is interested. (probs. not) stm32f4_cmsis_fft_serial_config.zip Edited 2024-02-07 14:33 by poida wronger than a phone book full of wrong phone numbers |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3801 |
Ooh, that could hurt some people - well found. John |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4233 |
Hi poida, This looks a bit like the issue with the RP2040 ADC. That 12 bit ADC also degrades to a 9 bit ADC because non linearities caused by bad capacitor matching on the chip. Thanks fo sharing. Volhout PicomiteVGA PETSCII ROBOTS |
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