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RFID tag sniffing

RFID tag sniffing

RFID tag sniffing

Hi everyone,

I have a problem and i need help,
I am building an access control system, using RFID 13.56Mhz,
but in order to save the battery's life, i have to implement a wake up system that senses that presence of the RFID tag, then it signals the MCU to wake up and take the necessary actions,

What is the best low power solution, easy to implement , for the wake up system,

Thank in advance,


RE: RFID tag sniffing

This seems to be the same question as was discussed here: http://www.eng-tips.com/viewthread.cfm?qid=427853

To reiterate what was discussed there, you will find it impractical to have the RFID reader constantly emitting the 13.56 MHz energy if your system is running on a small battery. You will need to use some other technology to "wake up" the CPU, which in turn would power-on the RFID reader circuit. Examples of other technology include things like a mechanical switch.

As Dan had hinted, "there are plenty of extremely low-power micros out there that can be woken from a deep sleep via an interrupt pin", which is really where you need to focus.

(If the battery is the size of a refrigerator, then you could leave the RFID circuit powered on all year. smile )

RE: RFID tag sniffing

VE1BLL's cite is apparently from the same OP, who should be pretty familiar with the response from that thread.

The OP needs to start with developing a timeline, i.e., how much time is involved in actual interactions with the badge reader? Once a robust timeline is developed, you can then determine the periodicity the badge reader needs to sustain to ensure reliable reads that don't take too long and frustrate users. The other thing that you need to know is how long it takes for the RFID chip to wake up and complete the transaction. Hopefully, between the these two time spans is a duty cycle and frequency that can minimize battery consumption while ensuring a reasonably reliable interaction.

TTFN (ta ta for now)
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RE: RFID tag sniffing

Thank you everyone for your answer,
and sorry for the redundant question,

V1Bell, i am looking for a non mechanical solution to detect the presence of a card,

Thanks in advance,

RE: RFID tag sniffing

Then you'll need a proximity sensor that is extremely low current to start with; and then further duty cycle it down to a tiny fraction of that. Maybe something based on a CDS photocell (assuming ambient light being blocked), or an IR beam being broken.

A friend owns a car with keyless entry and start, based on a transponder. He went away for a vacation, and came back to find his car battery flat. Apparently the car designers didn't understand how to balance these factors. They apparently left the interrogator running all day and night until it killed the battery. The solution would have been to put the system to sleep after say 24 hours, and then wake it up with a mechanical switch being jiggled in the door handle. My friend's solution was to wire a solar panel across his car battery.

RE: RFID tag sniffing

Thank you for your answer, I really learned from you,


RE: RFID tag sniffing

Hi everyone,

I found the schematic (attached) of 13.56Mhz sniffing circuit as per following project,

The project owner is providing the schematic and PCB layout as open source project,
However, it looks like the project is closed and the provided contact mail is no longer working,

Can someone here please help understand the attached schematic, sorry if this is a noob question, But i really cannot understand it,
Thanks in advance,


RE: RFID tag sniffing

The "RFID Sniffer" that you've linked to clearly has a push-button switch (S1) in series with the button cell battery (B1). It's a 'Push and Hold Button To Activate' design.

RE: RFID tag sniffing

Assuming that you do not need to allow access to anything weightless, maybe a simple switch, activated by pressure on a step-on panel may do.
I have an electronic scale, that turns on for a while when somebody steps on it, and it's button cell battery has lasted for years.

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