Seat it with the power off
Switch everything off, check which way round the Nano goes, push it all the way home, and only then connect power. To take it out, switch off first and then pull. Seated or lifted with the power on, a Nano behaves like a wrong seat for a moment, and the shield may get hot.
The rule
Switch the power off completely before the Nano goes into the shield.
- Unplug the USB cable, and anything else that feeds the Nano: a battery, or a jumper wire on a VIN or +5V pin.
- Check the direction. The Nano's USB-C end goes at the end of the shield marked USB, under the arrow that reads "USB IS ORIENTED THIS WAY".
- Push the Nano fully home, every pin of both rows in.
- Only now connect the cable.
To take it out: switch off first, unplug USB and everything else, then pull the Nano out.
Why the order matters
Nothing makes the contacts at the same instant. A Nano is never lowered or lifted perfectly level, so for a moment some pins are in their holes and some are not, and the ones that are in are meeting a shield they were not meant to meet yet. A Nano that is seated or lifted with the power on behaves like a wrong seat for that moment.
What that costs is that the shield may get hot. The next page spells out what a wrong seat joins, and the half-seated case is the last one on it. With the power off, none of it matters, because nothing is flowing through a contact while it is made or broken.
The shield has no power connector of its own. Its +5V comes from the Nano through the sockets, which is why the rule is about the Nano and the cable rather than about the shield.
How to know it is fully home
A half-seated Nano is also wrong. The pins on the Nano's underside are 8.4 mm long and the sockets are 8.5 mm tall, so a pin that is in all the way leaves no gap at all: the black plastic under the Nano meets the tops of the sockets. Any gap that you can see along either row means it is not home.
Do it with a thumb at each end, not with one hand in the middle, because a Nano pushed from the middle can sit with one end proud.
When it does not work
Unplug the cable, take the Nano out and look along both rows of pins for a bent one. If they are straight, seat the Nano again by the steps above. Nothing is lost if you were lucky; the rule is for the times when the contacts are not so kind.
Take the power off straight away, leave both boards unplugged until they are cool, then take the Nano out. Check the direction against the USB mark before you seat it again. The next page lists what each wrong seat joins.
Make sure the power is off first. Then work it up a little at a time, alternating between the two ends and pulling on the board's long edges, not on the USB-C connector or the chip. It never comes out level; with the power off that does not matter.
The Nano is probably not all the way home. Look from the side: there should be no gap between the black plastic under the Nano and the tops of the sockets. Switch off, press it down at both ends, and look again before you power it.
The USB mark, the one wrong way that fits, and which Nano pin lands on which shield hole in each wrong seat.
Which way round, and what a wrong seat joins →Edit this page — content/books/nano/seat-it-with-the-power-off.mdx
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