nrf24l01+ capacitor

Hi,

I see many people around saying that using a capacitor with nrf24l01+ improve a lot the range. I tried it, and it really doubled the range to me. It's a really good improvement. However many sites online say I should use a 1.0 μF or 8.2 pF capacitor. Other say from 1.0 μF to 10 μF, and othr also say that for best result I should always use 100 μF.

I understand the capacitor is to smooth the supplied voltage when power supply is not steady. So, why there is this "mess" of capacitor number? Why dont I just use the biggest value of 100 μF ? I understand this number is related to the capacity of the capacitor, why shouldnt I use the biggest value and make sure I have a lot of capacity to steady the voltagem?

I'd first check your power supply is adequate for peak transmission power. 10uF ceramic is likely plenty extra decoupling, I can imagine that in a system with inadequate decoupling the power out droops for a few microseconds at the beginning of a packet transmission, causing a greater failure rate / lower reliable range.

If your voltage regulator cannot cope without more than 10uF, it likely cannot cope period...

Anyway if you have a 'scope you can look at the power voltage on the nRF board and see if it droops...

I’ve been using the nrf24l01 for a while without any capacitor with no problems, or so I thought. I hadn’t realised that there are default retries and that unless you measure the round trip time you won’t know if the first or the fifteenth data interchange was successful.

There are a lot of variables like the voltage source, the wire length, the relative orientation of the tx/rx pair and the power level.

The best chance of working without a capacitor seems to be at the lowest power level.

I’ve found that an ordinary 47uF electrolytic works well.

A capacitor does work to smooth out volts. For small voltage drops dV the equation is

dv=it/C

where i is the current in amps
t the time in seconds and
C the capacitance in Farads.

The larger electrolytics are not as good at high frequencies as ceramics.

The problems arise when a piece of wire trying to maintain a voltage against a sharp increase in current does not act as a wire but as an inductor.

It acts like a high resistance for a short period of time and the capacitor has to maintain the current on its own.

Also the basic power supply will take a certain amount of time to increase its current output to handle the demand of a current pulse from the load.

I haven’t found any information from Nordic about how much decoupling is needed. I’ve ordered 22uF ceramics and hope that they will be large enough.

Thank you so much guys. @cjcj1949 indeed I dont need to use capacitors too but my range gets really small, no more than 40 meter. However today I tried a capacitor or 4.7u and I got 90 meters in clear sight on a grass field with no close external interference.

I tried 10u and the result was almost the same, 80 meters. Then I tried 1u and the result was 50m. Finally I tried 8.2 pF and I got 95 meters! This result does not look intuitive... So I really have no idea which value should be good.

Your formula dv=it/C may help me, I know the current may get up to 130 mA however I have no idea of "dv". How can I know it? Cause, according to your formula, if I have dv and it I can get C, right?

And finally, what would be the problem of using a larger capacitor than needed? The only problem would be the frequency that may no get as high as needed?

There is a lot of advice on adding an 8.2pf capacitor. I'm not sure how critical the value is but it seems to have a self resonant frequency in the 2.4Ghz band and it is filtering the rf rather than the logic. I've seen some advice for a 1uF ceramic and a 8.2pf in parallel. It does make sense.

Where did you get the 8.2pf, do you have a link?

Larger capacitors can cause a problem. One engineer reported problems after using 470uF. It caused a failure that could only be cured by powering down.

There are two issues: very quick voltage changes (high frequency) and voltage 'dips' when the transmitter in active for short periods. So a combination of smaller value but low inductance capacitors (like 0.1 uF ceramic) in parallel with 10uF (like 10 uF electrolytic) seems to be best.

Other factor is the small amount of 3.3V current available from UNO, Mega etc.

See: http://arduino-info.wikispaces.com/Nrf24L01-2.4GHz-HowTo

See the 'base module' HERE: which cheaply solves all 3: Separate 3.3V regulator, and 0.1 and 10uf capacitors. AND it makes it easy to connect to nRF24L01...

DISCLAIMER: Mentioned stuff from my own shop... among other things

@terryking228 really nice your idea! I liked that module but it does not reduce the number of jumpers connected to arduino... do you have any module that I can attach to nrf24l01+ and reduce the number of jumpers from 7 to anything smaller?

Your suggestion about the capacitor is really nice, I think it is the BEST! I will do that as soon as possible.

Hi,

10uF is probably the biggest I would go for the capacitor to provide reserve energy for the Tx/Rx.

Any higher and you might be placing current surge stress on the voltage regulator when you power up your controller. When you turn on your controller, the capacitor has to charge up to your supply voltage, the larger the capacitor the higher this almost instantaneous current is.

Tom.... :)

The 22uf ceramic works very well. It is a 0805 surface mount and fits between the pins. It is awkward to fit though unless you are used to surface mounts.