Ground plane, NRF2401 and radio PA level query

Other Hardware General Electronics
1

Hi.

I have a number of questions here on a project I'm working on. I'm using an NRF24L01 to transmit to a scoreboard. My project is created from a small circuit board, an Arduino Mini Pro, 3 diodes, 3 capacitors, a keypad an NRF and 2xAA batteries.

Questions:

  • I've created a ground plane on both sides of the circuit board (connected to the battery negative). On the underside of the NRF unit, the antenna has 5 pins (4 in a square shape, then 1 in the middle). All 5 pins seem to all be connected together to the GND pin on the small board (when checked with my multimeter). Does this mean I should connect them to my ground plane?
  • Also, all 5 of these pins seem to be connected together (again when tested with my meter). This is the 4 pins in square formation as well as the centre pin. Is that normal?
  • Is it best to connect at least the 4 pins to my ground plane to reduce interference and/or transmission distance?
  • To minimize interference, someone suggested wrapping plastic wrap around the NRF unit, then some tin foil. Would this really help minimise interference. I'm worried if moisture ever got into this unit, it might "short out"
  • Is it worth "covering" the NRF with a layer of plastic from a hot melt glue gun, then cover the whole unit in foil?
  • In the code, I've included the line: myRadio.setPALevel(RF24_PA_MAX);
    This can be set to MAX, HIGH or MIN. Can someone please explain to me what effect this does. I personally found that on MIN, the voltage to operate it could drop to 1.925V, whereas on MAX it had to be 2.030. Does this also affect transmission distance (or use extra battery current)?
2

Answers:

  1. The four pins in a square should be connected to your ground plane. The fifth pin, in the center, goes to the receiver/transmitter. The resistance from this pin to the other four may be fairly low (50 ohms or less) and you did not say what showed up with your multimeter.
  2. See #1.
  3. Connect the four pins to a ground plane to reduce interference and to INCREASE the range.
  4. You would be creating a Faraday Cage or Faraday Shield that will reduce interference but you may have side effects that are even worse. Moisture could be a problem. Static electricity from the plastic wrap could also be a problem. There are also mechanical issues involved. Think about how you are going to get wires and heat through this. My suggestion: Try with and without this. You may not need it.
  5. Maybe, but how are you going to avoid applying too much heat?
  6. You are adjusting the gain (and thus the power) of the PA (Power Amplifier). When two units are near each other on a workbench, you may want the power reduced. For maximum range, you want the power maximized. More power means more range but also increased current. You will have to make a trade-off between the range and the current used.
3

Thanks vaj4088 for those answers.

Yes, I was only measuring for continuity between the 5 pins. On measuring more accurately, it measure 2.3 ohms. So I assume that's normal.

In regards to mods to my current setup, I think I'll therefore try it out as is an do a little more testing on the power options. Thanks.

4

That's the antenna connector - a standard SMA socket is normally soldered there, or else a 1/4 wave
antenna wire direct to the middle pad only.

The RF circuitry consists of LC bandpass filter/matcher and to your multimeter an inductor looks like
a short circuit, whereas at RF it doesn't.