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I'm doing an rfid project that requires a read range of at least 5 inches or about 13cm. I'm using a nano with a usb port, a rfid reader from priority 1 design and a large antenna. The problem I'm running in to is that when I power the project from the usb port I get a pretty decent read range of 11-13cm. But when I power the project from a DC power supply the read range drops considerably.

After a lot of testing with various power supplies I believe that all my power adaptors are dirty enough to cause rf interference and reduce the range. Powering the project with a 9v battery and a 5v power regulator gives me really good range: 18cm with the largest antenna. But I need plug in power.

So how can I power this project in a way that gives me ultra clean power?

  1. I tried that same 5v regulator with a 5v adaptor and still had short read range.

  2. Someone suggested adding a smoothing capacitor between V+ and Gnd but I wouldn't know what size. I'm not an EE - I'm just a coder with a soldering iron.

  3. Is there a better power supply I can get?

[EDIT] Also just FYI, when I connect even only the ground wire the the computers USB port I get a much farther read range. So..

  1. Could it be a case of needing to ground the circut better as the switching power supplies only have 2 prongs and probably no real "ground". (Or am I making stuff up?)

[EDIT 2] What about a rechargable situation where my wall adaptor keeps a litium charged and the litium supplies clean power to the circuit?

Also I now know that I can charge my whole circuit with anything from 5 to 12 volts. In fact it would be better to have more in the 7 to 12 range than strictly 5v.

[UPDATE 3] Since this project is in my wall I was able to ground essentially to "earth" and that cleared up the noise. See this question as well: https://electronics.stackexchange.com/questions/230024/grounding-dc-project-to-clean-rf-noise

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badweasel
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2 Answers2

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This is what I use, although admittedly not in your application. I run it from a 12V wall adaptor and adjust the output voltage to suit my requirements. The input should ideally be at least a couple of volts above the output(depends on current and temperature at 25degC and 20mA it's > 1.6V and 1.5A at the same temp it's > 2.7V).

Circuit Diagram

Another alternative if you want to really go to town would be to repurpose an old computer ATX or similar PSU. There are plenty of guides out there and it's a straightforward job.

Bra1n
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I think the problem is not the voltage but the magnetic field, so maybe better to use a faraday cage (a metal box) around the power supply and connect it to output DC ground.

ScotTinow
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