As an off-Topic to my main question, regarding Robodyn's Uno+Wifi - it seems that Wifi does not work ( fail to connect and fail find any network ).

Juraj advised to use External Antenna ( did not work ) and try to make an RF calibration as shown on espressif's site. Which I fail to understand how it is done.

a) Can anyone help with RF Calibration ?

b) Might it be another reason for that ?


EDIT_1 Just to be clear, a sלetch was uploaded and executed successfully to the ESP8266 module (Basic WiFi connect and network scan ).

Edit_2 close up pic

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    Every ESP8266 schematic I can find has a 5.6pF capacitor between the LNA pin and the antenna. Robotdyn's doesn't - it has a resistor. Looks like they aren't that great at designing RF circuits...
    – Majenko
    Oct 24, 2020 at 16:30
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    I'm not so sure. I'm going by the schematics here, but they don't seem to match what I am seeing in the product image. What I think is R13 looks to actually be a capacitor... It looks like there's no real relation between the published schematics and what is really on the board.
    – Majenko
    Oct 24, 2020 at 16:35
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    @Majenko - See Edit1 please ( to be sure )
    – guyd
    Oct 24, 2020 at 16:36
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    Looking at the colour of that capacitor for the u.FL it looks way higher than 5.6pF. More like 1nF.
    – Majenko
    Oct 24, 2020 at 17:00
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    @Juraj - how can I do that ?
    – guyd
    Oct 24, 2020 at 17:23

1 Answer 1


You can't do anything else with the RF calibration then to clean the flash area where it is stored. There are two reason for doing it:

First is reason to delete the RF calibration area is, if it was written by different version of Espressif SDK, including changing between AT firmware and Arduino. Then it is almost always wrong. I think they changed the data structure so some values are swapped.

Second reason is if the SDK did the calibration in wrong conditions like without antenna.

There is not much information about RF calibration. The FAQ has "Please erase the RF parameters to trigger overall calibration."

The AT firmware reference has (addresses for 4MB-C1):

  • blank.bin 0x3FB000 Initializes RF_CAL parameter area.
  • esp_init_data_default.bin 0x3FC000 Stores default RF parameter values, has to be downloaded into flash at least once. If the RF_CAL parameter area is initialized, this bin has to be downloaded too

The esp8266 Arduino core writes the data of esp_init_data_default.bin as part of the sketch's binary.

EDIT: the SDK does the 'digital calibration' at boot. it takes some microseconds. it is not done at every boot, but after some count of resets. this can be configured in the init section

  • Thank you again. From FAQ, I don't have any operative steps what to do.
    – guyd
    Oct 24, 2020 at 17:22
  • flash blank.bin to 0x3FB000 or erase the entire flash.
    – Juraj
    Oct 24, 2020 at 17:28
  • Erasing using esptool.py ? since erasing using Arduino IDE did not solve it
    – guyd
    Oct 24, 2020 at 17:32
  • Arduino IDE uses esptool.py. btw. what are your Tools menu settings?
    – Juraj
    Oct 24, 2020 at 17:33
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    Nope - setting to 4MB, nor to Wifi Arduino under ESP8266 didn't make it :(
    – guyd
    Oct 24, 2020 at 18:16

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