QT PY 5V as power input - Diode?

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wallan
 
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QT PY 5V as power input - Diode?

Post by wallan »

For QT PY boards, I see the note from the product page "You can also use the 5V pin as a voltage input but you must have some sort of diode (schottky, signal, power, really anything) between your external power source and this pin with anode to battery, cathode to 5V pin."

But I'm having trouble parsing the instruction: there seem to be three nets discussed (external power source, 5V pin, "battery"), while the initial instruction suggests the diode should be inline with the external power supply to 5V pin. Could you help clarify the proposed diode configuration? Thanks much!

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dastels
 
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Re: QT PY 5V as power input - Diode?

Post by dastels »

"anode to battery" really means anode to the + of the power source, which isn't necessarily a battery.

So ...
- ground of the power source to ground on the QtPy.
- + (e.g. 5v) of the power source to the anode of the diode
- cathode of the diode to the 5v pin/pad on the QtPy.

The cathode of the diode is the end with a stripe. See https://learn.adafruit.com/assets/21855

The diode will let the external power supply voltage through to the QtPy, but will prevent it from going in the opposite direction. E.g. if you connect USB it will power the board with 5v... you don't want that to go to the external power source. Yes, that's a rather simplistic and somewhat inaccurate description, but it suffices for this.

Dave

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