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I want to connect my YUN Rev. 2 to 7.4V. I read that the older version only provides exactly 5 V at the Vin Pin. Is the Rev. 2 similar to it? I read that the power supply should be improved, but what does that mean? I just tried to connect the Vin to regulated 5 V by a power supply board, but it didn't work. If I connect it to the 5V Pin the board is working, but I think this isn't recommended. So has anybody experience with that board? Thanks for your answers.

  • are you sure 5V pin is working and Vin is not for supplying power? – Juraj Sep 16 '18 at 14:19
  • Yes, I just tried it several times. Even if I change the voltage. – Bert Sep 16 '18 at 14:52
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For version 1 VIN is connected, through a Schottky diode, to the 5V rail. That means you can only provide, at absolute most, 5V plus a little bit for the diode drop into VIN. The 5V pin can only source power on the Yun, since it is also connected to the 5V rail through a Schottky diode.

In effect the two pins form the "In" and "Out" of the 5V power.

However in version 2 the 5V pin's diode has been removed, and the VIN's diode has been reversed. VIN is now known as "5V_OUT".

So the 5V pin can be used for both in and out, and what was VIN can only be used for power out.

To provide more than 5V to the Yun you will have to first pass the voltage through a regulator of some form. Since you want to use 7.4V it sounds like you are using 2S Li-Ion (or similar) batteries. Because of that I'd recommend a switching regulator, rather than a linear one. I commonly use 5V UBEC modules from my favourite RC model supplier.

For version 1 you will provide it to VIN. For version 2 you will provide it to 5V. Quite why they'd change something quite so fundamental as the power pin arrangement from one version to another is beyond me. It would cause havoc with compatibility between versions with certain shields.

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  • The regulator I just tried provides 4.9V. I just tried to use an transformer and it was the same, even when I changed the voltage. When it's connected to the 5V output the Yun is working fine... I would try to use an other regulator, but I thought 4.9 V is in range or not? Your right, I want to use two Li-Ion: – Bert Sep 16 '18 at 14:50
  • According to the schematics you should not be able to supply power through the 5V pin, and you should not be able to draw power from the VIN pin. Maybe a mistake was made during manufacture and the diodes are backwards. – Majenko Sep 16 '18 at 14:52
  • Hang on - yes, it's changed on V2 for some reason (why would they change something fundamental like that? Because they're idiots, that's why). – Majenko Sep 16 '18 at 14:54
  • but it is good trick. if someone expects a build-in regulator, Vin would not work and supplying other then 5 V to 5V pin would be stupid – Juraj Sep 16 '18 at 15:05
  • @Juraj Better would be to put an actual regulator on the board... That way VIN works like VIN on all the other boards with the same footprint... – Majenko Sep 16 '18 at 15:13

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