I’m connecting a clone breakout board powering the pn532 from 3.3v (might be the case with other methods too!) using the following schematic

(credit DanyO for his Py532lib tutorial ).

I’m experiencing the following problems:

  • board disappearing when scanning the i2c bus
  • tag disappeared errors when reading a tag (libnfc 1.7.0)
  • error during tag reading
  • using debug level = 3 as suggested on the libnfc forums, the situation does not improve a lot

I’m not an electronics engineer, but it happened to me sometimes that devices are not correctly powered, so when I faced this problem, two piece of info came into my mind:

  1. I read more then once in the RPi forums that the 3.3v line might be dirty due to high integration in the board
  2. PN532 breakout board can also work with 5v power supply so it might become picky when powered via 3.3v

My proposed solution is to put a 10nF decoupling capacitor in parallel with the 3.3v power supply, as near as possible to the PN532 chip.

After I added the capacitor I was able to read a mifare classic 1024b three times in a row without errors (was not even able to start that before the mod).

I’m still experiencing some problems from time to time, so it might be the case to put another 100nF capacitor in parallel and, in extreme cases, add a 2.2uF-4.7uF electrolitic (add, not switch, from my googling around), but don’t go too high (disclaimer: if your Pi reboots or the 3.3v line blows, don’t blame me!) because that may introduce high current load at startup and some parasite effects that might nullify the decoupling benefits.

Here is the mod:

Hope this is of any help.


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Spiderman helps the bat

March 3rd, 2012

In Summer, we have a lot of mosquitoes, mainly because they’ve been proliferating in our area, but also because we are near to a stream of water and it’s much easier for them to survive.

We’ve been using insecticide products to keep our house surroundings safe, but it’s a loosing battle because mosquitoes are very hard to eradicate and because you’d have to make all the neighbours using those products.

For the moment we are using mosquitoes net for the inside of the house, but the outside at disk an agonizing pain every time.

That’s why we started thinking about bats: they can eat a lot of insects every night and are a bio-friendly solution.
All the stories about drinking your blood or hanging on your hair are just rumors, so they are perfectly safe and they almost don’t make dirt.

Italian bat strains are very small and very friendly, so you just need to put a wooden bat house on a wall or on a tree, that has good visiblity from the sky and you’re done!

Today I wanted to install a bat house on the walls of my house.
The guidelines say it has to be a safe place for our local bats to settle there: at least 2.5m from the ground.

Unfortunately the house also have to remain as far as possible from metallic objects, and I didn’t have a proper ladder to go up 2.5m+ and below the roof.

The only solution was to go up the little piece of roof over the first floor and use a ladder someway to go upper.
After all it was too dangerous (a ladder on a roof?), so I actually had to ask the Spiderman to hang on the wall, go up a couple of meters, drill a hole and fix the bat house where all the requirements where met:

  • Easy to clean and maintain
  • Safe for the bats
  • Easy to watch
  • Far from metallic gutters and from the ground

And there is the first bat house of the neighbourhoods 🙂

Hope someone finds it useful!


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