Nano IOT 33 needs reset when using Vin power

I've found that when powering my 2 Nano IOT 33's with 5V on their Vin pins, that the program won't start executing until I press RESET. On all other nanos I've used, applying power to Vin just starts everything, and I've hardly ever used RESET at all.... Is this normal? Do I need to put a RESET button on the exterior of my project boxes now?? This doesn't occur when using USB port power.....

Hello, this problem happens occasionally to the nanos and it is that the internal power on reset does not work well when feeding it with only 5v through the Vin, keep in mind that Vin is connected directly to the internal regulator and you need a couple of more volts so that this regulator a stable voltage of 5v. You have three ways to try to fix it:
1- connect an electrolytic capacitor of about 10uF between the Reset pin and GND, with this you add an external power on reset that takes longer than the internal one, (it is as if you press reset a little later).
2- power by Vin with at least 6.5 / 7v
3-If you are sure you have 5V, feed it through the 5V pin.
If either of these doesn't work, discard the plate and use it for testing only.
Greetings.

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Thanks for your helpful reply - the 5V was a completely arbitrary choice, I chose it as the box said >4.5V was ok..... I'll change out the 7805 :slight_smile:

The Nano IOT 33 does not seem to have a 5V pin. @gonpezzi is confused with the ordinary Nanos.

There is a 5V pin, but I thought it was for output, and you need to solder a jumper for it to work.... I have plenty of 7809's I can use in place of the 7805....

Thanks, looked at the schematic and it's called Vusb.

On a Nano 33 IOT, there is no protection if you feed 5V into the 5V pin and connect USB at the same time. Glad you do not go that way.

Indeed, I have reviewed the schematic and @sterretje is right and you could not connect the 5V to VSB and the USB port at the same time, the only protection it has is between the USB port and Vin.
Yes, you can use the 7809 to power through Vin since this input supports 4.5 to 21V and you would be protected to use the USB port at the same time.
The latter (4.5 / 21v), makes me think that at the beginning you were using a 4.5v power supply and it shouldn't have failed you at the start, perhaps the internal power_on_reset will still fail at the beginning. If this happens to you with 9V for Vin you will have to place the capacitor that I told you before.

I changed the 7805 I was using for a 7808, and it is working fine.... thanks very much....

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