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RFID circuit problem

RFID circuit problem

Hi everyone,

I have a problem and i hope that someone can help with it,
I have designed a circuit that contains the following;
- controller
- custom RFID reader circuit based on MFRC522 including matching circuit and EMC filters
- indication (leds and LCD)
- logic level converter
- the circuit is powered by a power 5v power supply

I have a problem that sometimes RFID reader fails to work, and the circuit seems to be holding much of static charges,
but when i touch any terminal (and the charge is dissipated), the reader works again after resetting the system,

Can anyone help me with this issue,

Thanks in advance,


RE: RFID circuit problem

How do you know it's a "static charge" causing an issue? What portion of the circuit is holding said charge? What terminals are you touching to bleed off of this charge? How do you know the charge is gone, as most people are a walking battery waiting to dissipate their charge into something else?

Dan - Owner

RE: RFID circuit problem

You've not proven causality, only correlation.
Since you have to reset, why wouldn't Occam's Razor point to your controller getting lost in its code?

Your description claims a 5V power supply, so there is already a static dissipative path through the supply, and therefore, it's unlikely for there to be static charge in the normal sense. That said, it's not unlikely that you left floating nodes in your circuit that have floated into undesirable states.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
FAQ731-376: Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list

RE: RFID circuit problem

Thank you everyone for your support,

I think the problem is floating nodes as IRstuff said,
Am i supposed to leave no floating pins in every chip (microcontroller, logic IC, MFRC522), and what is the best method of doing this,

and if the project will take another phase and be supplied with battery, is there something else to be considered???

Thanks in advance,

RE: RFID circuit problem

Floating input nodes are only an issue if, and only if, you are depending on those nodes to provide stable logic signals.

Your question about battery power is irrelevant; there are literally BILLIONS of circuits that are battery powered, such as your phone, which have ZERO problems with locking up, static electricity or otherwise. A common mode on a circuit is mostly irrelevant if it does not have to physically be connected. There are millions of Rokus with RF remotes that have ZERO problems with lock up.

Your static problem is most likely a wild goose chase.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
FAQ731-376: Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list

RE: RFID circuit problem

To add to IR's earlier comment about floating pins...

Outputs are (generally) fine being left unconnected. Inputs, not so much... not only can they lead to odd modes of operation, they can waste precious power in battery-operated circuits.

Dan - Owner

RE: RFID circuit problem

Many thanks for your answers,


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