@mfalkvidd OK I'll try that. But as expected, there is no suitable capacitor left over in my box.

@gohan the LED does not flash fast. It goes on for a couple of seconds and is off for about half a minute.
I didn't add a capacitor, is that really necessary? What capacity do you recommend?

@mfalkvidd the main error seems to be (with description from log parser)

51 TSF:MSG:SEND,3-3-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
Sent Message
Sender: 3
Last Node: 3
Next Node: 255
Destination: 255
Sensor Id: 255
Command: INTERNAL
Message Type:I_FIND_PARENT_REQUEST
Payload Type: P_STRING
Payload Length: 0
Signing: 0
Failed uplink counter: 0
Status: OK (OK=success, NACK=no radio ACK received)
Payload:
6152 !TSM:FPAR:NO REPLY
No potential parents replied to find parent request
6154 TSM:FPAR
Transition to Find Parent state

But this does not help me, because still it works fine if powered direct from FTDI.

My node shows a curious behavior. It's based on a pro mini 3.3V, a DHT22 and a NRF24L01.
When switching on the battery, the node goes into a boot loop showing up the red LED repeatedly.

If connected via an FTDI Board to USB it boots up, connects to the gateway and shows up in my domoticz. Then the Sensor data come in correctly as from the other nodes.

So I think this could not come from the code, it must be something with the wiring. In both cases i find the correct 3.3V on all places. There are no shortcuts i could find. From the FTDI board I need to connect GND, CTS, VCC and DTR for the node to work.

The battery pack (2x 1.2V 750mAh ) is connected to GND and VCC over a Step-up power converter.

Any suggestions where to search for the reason?
Thanks

@alexsh1 yes, I'm sure. Up to now it is only a serial gateway with direct connected sensors.

Do you love curiosity?
After nearly a week of running, my gateway stopped working out of the blue.
I found out, that I am where I began. The same effects as described in the original post, but with the SFE library.

So I tried it again with the original Adafruit_BMP library and --- it worked !

Maybe there is something with my hardware. I'll go and get me another Arduino Board from a different manufacturer and try it again.

@alexsh1 yes, that's what I found out after buying those two devices. But for some early tests and freshen up my rusty programming skills it is good. Maybe I change the hardware for the final installation.
But it is still curious, that those two libraries won't work together. I tried to understand the code, but up to now did not find a clue, what could be the reason.

@sundberg84 So I found the error while using the SFE_BMP180 library: there is a need for a short delay before the getPressure(). So now it works.

But why not with the Adafruit_BMP085 library I do not understand.

Thanks a lot.

@sundberg84 still searching for a solution.
I tried to rewrite the sketch, starting from the working single sensor gateway with the humidity sensor. In the domoticz log I can see the messages from the sensor come in and the value is updated. Then I added line by line the necessary code for the pressure sensor.
The "present(ID, S_BARO);" did not have any results, but the humidity still updates. After adding the "send(msgBaro.set(pressure, 0));" the data delivery stopped (does it make any difference here to have a "0" instead of "1" for the ack? It's the only difference to your script I found.)
It's the same the other way around: starting from the gateway only with the pressure sensor. As soon as I add the send command the function stops.

This led me to the idea, that there must be something wrong with the present() or the library. I searched for another library for the BMP180 sensor and fond https://github.com/sparkfun/BMP180_Breakout. And it worked directly. The only problem is, that now the values are incorrect. I get 867hPa instead of 1018hPa.

Thanks for your help!

@sundberg84 the connection is a regular USB cable which works fine on other devices too.
But I am one step ahead: I changed the sketch for only using the humidity sensor and it worked as expected. The values come in and I see them in the domoticz log, also the "last seen" in the dashboard updates.
Then I did the same for the pressure sensor and it didn't work. For this the solution was really easy: a type mismatch. I defined "pressure" as "long" and "lastBaro" as "float". After changing both to "float" the single sensor gateway woks fine. I see the pressure sensor in the devices list and the values are collected.

But when I connect both sensors, still nothing works.