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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Hey, it was back in 2006, when I first posted about my Samsung E700 poor man’s repairing.
Back then I was able to make the poor phone flex work for another couple of months.

Now here’s a new curious story: how I tried the flex switch.

When you need most your mobile phone

I was riding my bike back home with my good old Motorola C650 when I dropped it without knowing that.
It turned out it was smashed by some vehicle some time later and a man doing jogging found it.

Crazy enough he tried to use it, but nothing was showing up on the display.

Hey, what the hack is this story about? That’s insanely out of topic!!

Yes, I know, but if you want the real thing, you’ll have to read thru this…
So: finally the wise man put my SIM back in his phone and called the “home” contact.
Yep, I definitely answered. I wasn’t even aware I had lost the phone! Anyways to cut it out my phone came back into my hands! Thanx Marco!!! πŸ˜€
I guess it wasn’t much of a gain, keeping a not working mobile! πŸ˜‰

I was really happy because I got back my 15EUR worth of calls on my SIM and the phone, though broken, seemed still usable.
After a cose look, it seemed the display was broken, so i thought: just try to place a call just to be sure a display switch will do the trick.
Nope, the phone does not place nor receive calls: I don’t think that a new display is a good idea!

But…. BUT! Hey, I got that nice E700 back in my closet, waiting for an extreme repair!!!

The real thing
I decided it was time to get my E700 back to work, so i ordered a new E700 flex (without displays) and I tried to unsolder the main display and to solder it back on the new flex.

Yep, I failed!

E700 dismantled flex

First of all the external display: it is just stitched on the board. I don’t know you, but i’ve seen tens of electronic caluclators and the always have this absurd way of stitching the display or the solar cells: that’s the same on the external display.
The bad thing is that you’ll never get your stitched contacts back! They just get disintegrated πŸ™

No problem, the main thing is the internal display, or i’ll never be able to use my phone again.
Well the display has a nice soldered couple of contacts for power, so with wathever solder you have, you’ll be able to detach that.
The real problem is when you try to unsolder the data contacts: impossible, you risk to end up with a cut out piece of plastic.

E700 displays

Well I wanted to try anyways, so I started soldering everything and found a decent status to test: nothing. Pure black (except for the white backlight leds).

E700 Flex Repair Powered

First: don’t even think of doing that if you don’t have the right tools

Second: even if you have the right tools be aware that anything could go wrong (expecially with the stitched external display). For the internal display here’s what may go wrong (in order of probability):
– wrong unsoldering: contacts broken
– wrong soldering: solder may damage your phone
– defective flex: you might to the thing perfect, but something’s not working

E700 broken flex

Third: you could just simply buy a complete display spare for less than 15EUR and just connect it (after having read my guide on dismounting the phone πŸ˜‰ )

Happy bidding! Can’t wait to try my spare… πŸ˜€


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