I am using a NRF24L01+ 2.4Ghz radio transmitter to talk between Arduino's. I was having issues with them frequently cutting out for short periods of times. I noticed that when I added 100uF capacitors to the power pins of the NRF, I had almost no packet drops. I added 100uF tantalum capacitors to my circuit board design, but when I plugged in the NRF's, I was still getting the same issue as before. (I'll be it slightly better). When I soldered the capacitor onto the leads manually, I was using an Aluminium Electrolytic capacitor.
I heard that these NRF's are incredibly sensitive to voltage noise, so adding capacitors is good for them. But my suspicion right now is that for this case, Aluminium Electrolytic capacitors are betting for this purpose than tantalum (And cheaper). Am I right in this assumption?
It's not the caps, it is the current capability of the NRF module power supply and you've said nothing about how the module is powered. Using a 3.3 v LDO regulator supplying the module (with the proper bypass caps for the regulator ic) and you'll have zero problems and not need extra mystery capacitance to make it work.
As with so many electronic problems, common ones can usually be traced back to an improper or poor power supply. The NRF modules are an excellent example of this common mistake.
jackrae:
Tantalum should have worked. Are you sure you had it the correct way round; the bar on an SMD tantalum is the positive end.
The tantalum capacitor is placed correctly, I have looked at the datasheet multiple times.
avr_fred:
As with so many electronic problems, common ones can usually be traced back to an improper or poor power supply. The NRF modules are an excellent example of this common mistake.
The NRF is connected to its own dedicated 3.3V voltage regulator which can supply up to 500ma. Power is not the problem, as I can set the NRF power consumption level. Even when the NRF was hooked up to a normal Arduino, the NRF would not have connection problems when a Aluminium Electrolytic capacitor was placed onto it. And the pins of the Arduino only support 50ma.
I think "soldered directly to power pins" is much better than "connected into breadboard nearby". The breadboard and jumper wires have significant resistance. Also you need to think twice before connecting regulator. To get some reasonable regulation the "layout" is important when you are using "large" currents.
mschindl:
The tantalum capacitor is placed correctly, I have looked at the datasheet multiple times.
The NRF is connected to its own dedicated 3.3V voltage regulator which can supply up to 500ma. Power is not the problem, as I can set the NRF power consumption level. Even when the NRF was hooked up to a normal Arduino, the NRF would not have connection problems when a Aluminium Electrolytic capacitor was placed onto it. And the pins of the Arduino only support 50ma.
Do you have bypass capacitors around the regulator?
Do you have bypass capacitors situated around your PCB?
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Can you post an image of you PCB pattern please?
Thanks.. Tom..
mschindl:
. . . I added 100uF tantalum capacitors to my circuit board design, but when I plugged in the NRF's, . . .
. . . When I soldered the capacitor onto the leads manually, I was using an Aluminum Electrolytic capacitor. . . .
These aren't equivalent tests. For decoupling the mechanical circuit layout is a critical part of the design. Long wires and/or circuit traces add inductance and resistance that reduce the effectiveness of the decoupling capacitor. As a rule the bypass capacitor should be as close to the load as is reasonable and the traces for power and ground should be short and wide.
So playing around with capacitor placement I found something interesting. When I disconnect the NRF I get 676 drops per minute. When I put the tantalum cap on the SMD pad I get 430 drops per minute. When I put the Aluminium Electrolytic cap on the SMD pad I get 359 drops per minute. When I put the Aluminium Electrolytic Cap on the 2.54mm pins of the NRF, I get 1 drop per minute.
No Connection: 676 drops
Tantalum on SMD: 430 drops
Aluminium Electrolytic on SMD: 359 drops
Aluminium Electrolytic on pins: 1 drop
Is it possible that my copper traces are screwing with something? They are about 2mm long and 0.5mm in width.
mschindl:
Is it possible that my copper traces are screwing with something? They are about 2mm long and 0.5mm in width.
So you have everything mounted on a custom PCB?
Yes thin tracks will limit current, and capacitors on the supply fr the NRF should be a close as possible to the NRF, likewise the 3.3V regulator.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Can you post images of your PCB pattern please.
Thanks.. Tom..
