On the weekend, I got my ESP32 -WROOM-U modules, the "U" standing for a Ipex connector instead of the built-in antenna. Unfortunately, I didn't find any 30-pin dev boards with that module already mounted, so I replaced them myself on the ones I already had.
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As Martin already mentioned before, the noise coming from the WiFi part of the ESP32 does not really change, it is still audible with the external antennas. I have no idea, if the external antenna has some other advantages for this firmware, for example less noise for the SBUS signal, but I will use them for future vehicles and maybe find out in the process. I assume, that these external WiFi-antennas (not sure if it's for Bluetooth, too) are probably mainly for range extension.
For now, there doesn't seem to be a practical advantage using a external antenna (although it probably doesn't hurt either).
I also have some notes to share for the MP1584 switching regulator. Some are pre-set to a fixed voltage, others come with a potentiometer.
Usually, I replace the pot with a resistor, since it can't be accidentally changed or it's wiper lose contact over time.
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The space the pot leaves behind fits perfectly for a 0508 SMD resistor, where 27 kΩ is the "officially" used value for 3.3 V (3.4 V actually) and 43 kΩ for 5 V (at little bit less actually).
Since there are only so many values available, I found a nice way to fine tune the voltage is by putting another resistor on top of the other one (in parallel).
Using a 27 kΩ and a 1 MΩ on top, will give a more precise voltage of about 3.3 V.
Using a 47 kΩ and a 680 kΩ results in a voltage slightly above 5 V. Lower values, for the piggyback resistor, will raise the voltage more (because the resistance in total will be reduced).
You can calculate this yourself: 1 / (1/47 + 1/680) = 43.961 (kΩ)
The formula vor the voltage is: (R1 + R2) / R2 * 0.8, for example: (43961 + 8200) / 8200 * 0.8 = 5,089 (V)
R2 being the resistor already in place (see picture). If it has a different value, this value needs to be used (but I've never seen a board with another value than 8.2 kΩ).
In reality, it doesn't really matter if the voltage is a little bit lower or higher. I like to set it a little bit higher, since with more current flowing, the voltage usually drops, too.
And then, I was testing out, why my resistor calculations, for current limiting the LED lights, were always a little bit off with reality, and I ended up selecting the right resistor, by simply testing it with a bench power supply and/or a amp-meter.
Turns out, that it's really important, how much current flows, while measuring the forward voltage. The forward voltages measured by a multimeter or a "Transistortester" (ATmega328 based device) are not only too low, they also allow no conclusions by simply adding an offset. Multimeters also have the disadvantage of a limited voltage range.
The best way to get the "real" forward voltage, seems to be to use a bench power supply, limit the current to a reasonable amount (like 15 mA) and let the voltage adjust automatically. For the regular China LEDs, I get the values seen below.
I found this to be quite interesting, but in reality it doesn't really matter, when it comes to the brightness of the LEDs.
I usually aim for 10 mA for 3 mm LEDs and 15 mA for 5 mm LEDs, sometimes 20 mA for headlights.
But I get the feeling, that I could go way lower, without losing much brightness at all. But then again, compared with the power consumption of the rest of the vehicle, it doesn't matter either way.
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As you can see, I've spend a lot of time finding out stuff, that doesn't really matter or other people already knew.
