Feather RP2040 usb voltage input limits

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JBenziger
 
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Feather RP2040 usb voltage input limits

Post by JBenziger »

Hello Bill,
I hope to rewire my Feather RP2040-based digital thermostat that I made, with your help, and wire it into my 12 volt RV coach circuit. The easiest way I can think of is to connect via the usb c input. The DC-DC converters I can find will take the 12V down to 5v and 3A. The RP2040 runs on 3.3V and I think may convert the input voltage down to 3.3V, but I'm not sure. Will this work? Is there a better way to accomplish my goal?
Thanks very much,
John Benziger

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dastels
 
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Re: Feather RP2040 usb voltage input limits

Post by dastels »

Powering with 5v through the USB connector is the easiest, safest way. Alternatively you can provide 5v at the USB pin. The problem with that approach is that the USB pin is directly connected to the USB connector without any protection. If you have 5v on the USB pin and connect USB, there will be problems because you would be connecting 2 power sources.

Dave

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blakebr
 
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Re: Feather RP2040 usb voltage input limits

Post by blakebr »

Hi,

Voltage stability in automotive environments can be very problematic. You may want to put a 1N4735A Zenner diode across the 5 volt buss. It will absorb a short duration overvoltage without issue. It will short out and die a heroic death with a large overvoltage thus protecting things on the 5 volt buss. If you worry that 1N4735's 6.4 volts is too high, you can try a 1N4734A diode @ 5.6 volts.

There are fancier 'crowbars' that use an SCR, Zenner diode, resistor, and capacitor.

Bruce

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dastels
 
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Re: Feather RP2040 usb voltage input limits

Post by dastels »

You'd want to use a very good 5v regulator and some serious smoothing/cleanup capacitors.

Dave

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JBenziger
 
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Re: Feather RP2040 usb voltage input limits

Post by JBenziger »

Hello Dave and Bruce,
Thanks very much for your sage advice. I feel better going forward.
John Benziger

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JBenziger
 
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Re: Feather RP2040 usb voltage input limits

Post by JBenziger »

Powering digital thermostat off new MacBook Air and off internal battery
Featherwing oled display (id 3192) seems to have failed (see photo)
Left side of display has many pixels that have 'dropped out'. Bottom left text should read '_Set Temp:'
This oled display (showing virtually the same image, just different temp numbers) has about 80 hours total use. Have some pixels burned out?
Guess I will need to buy a replacement.
Do you have any observations?
Thanks, John Benziger

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