Transmission issues, looking for ideas

[mortommy]

Hi,
I'm experiencing an issue in transmission and I'm looking for ideas to fix it.

I have a GW implemented by a Nano (5V) powered via a USB connected to a PC and a NRF24L01+ Radio unit with no antenna and the classic decoupling capacitor; there are 6 nodes implemented by mini 3.3V and one mini 5V. The nodes are powered in different ways (button battery, AA batteries, power units) and I'm having trouble with just one: the 5V mini powered by a power unit and a step down converter (AMS1117) to power the NRF24L01+ Radio. The unit receives command from the GW but the GW seldom receive command from the node. The nodes is not in a difficult position is even better of others (I have one node outside and one inside a metallic cupboard and actually even if it gave me some troubles at the begging now is working).
I already tried some shoots:

• moving position, and I get better result if I move it in a highest position, but I'd like to not move it
• connecting the step down converter directly to the main 5V voltage regulator and not to the Vcc arduino pin.
• changing the unit radio.
• changing the decoupling capacitor (also with greater values)
• moving GW position, it looked better but I'm not sure if fixed the issue and I lost transmission with another node.

I know NRF24L01+ needs nice power but I have some nodes powered by button battery with no issues and this one has a separated power unit, could be the AMS1117? The poor power affects only transmission? Do you have any ideas? I'm also thinking to change the GW unit radio with the antenna version, could it help?

Thank you.

[TheoL]

@mortommy Have you tried another radio for that node?

[mortommy]

Hi @TheoL ,
thank you for your answer.
I changed the radio module once, because I realized that a stock of new radios I bought from a new seller was not nice so I replaced with a new one I bought from the seller I used before. Just to exclude this option I'll try to change again the radio module.

[mortommy]

Unfortunately no luck with the radio module replacement, I still have same issues. I noticed that moving around the node it could be is a problem related to the position, because I get communication to the GW only if I place it in a highest place (10 cm more is enough). I moved down the GW and it looks better but as I said before I noticed some problem with another node. Should I try the radio module with antenna for the GW?

[TheoL]

@mortommy I'm really interested in the circuit you have for this node. I have one node that is sometimes stable for a couple of hours or days. And sometimes stalls.

What I've done is, I powered everything from an adapter (including the radio). For the moments it's running stable for almost a week.

The reason why I ask you for you circuit, is because your problems sound the same as mine.

[mortommy]

Hi @TheoL ,
the node has this kind of logic schema:

and the gateway:

Yesterday after I saw this long discussion I tried this trick on GW but at the moment doesn't seem to be much better.
As next step I was thinking to modify the GW not powering the radio module by the arduino regulator but via AMS1117.

[Yveaux]

@mortommy said:

decoupling capacitor

What capacitance did you try?

[mortommy]

4.7uF and 10uF

[scalz]

@mortommy how all modules are interconnected? with airwire? on proto board? etc.
what's the external board dc/dc regulator?
ams1117 seems to be 16v max but depending where you bought it may be not able because it could power your mini+radio.
If you have stability issue with this specific node, and it works fine with batt (did you try it?), it could be some bad parasites..
you could simply put few small capa, in //, (for instance 10n, 100n, 1u) between your AC/DC and the regulation to try to filter a bit some frequency. but it's better with a ferrite bead with one or two capa.
AC/DC, bad regulation, wires etc... can be a nasty combo sometimes

[mortommy]

Thank you @scalz ,

all modules are connected by dupont jamper, partially soldered. The external regulator is based on 78L05.
But maybe I have something. After your post, I thought I had trusted too much my AMS117 module and I checked the voltage value between Radios' Vcc and Gnd and I found 2,42V, that it looked too small. I had another AMS117, and I switched with this new one and I have now 2.80V. It is a small value, isn't?

[scalz]

@mortommy
sure, if you're circuit is only what you explained, that's strange you should get your 3v.. and what if you only use 78l05? as you're doing with your nano (5v). if these are non PA radio, this should be enough i think with some capa.
Or maybe use another regulator..
For instance, I have a device which use Hilink so 230V to 5V. then I only have MCP170x like, to power my circuit (atmel+radio). works ok for me but it's rfm..

[mortommy]

some news here: I changed the GND jamper from the external regulator to the AMS117 because I noticed the Vin was less than 5V; now the Vin power went back to the expected value and the radio module has now a stable power of 3.3V. Unfortunately I didn't get normal communication from node to GW

[mortommy]

Juts to leave a record about the issue. I changed the GW radio module with a NRF24L01 + PA + LNA one, powered by the AMS1117 and the ugly fix. Everything seems to working fine now.
Thank you to every one.