@mfalkvidd many thanks for the very quick and polite reply.
It is working now and this solution is much better way, than using an additional ESP as gateway.
Even though I got on the wrong lane, I learned more details from your excellent guide, than from the "make", "make install" from the MySensors page ... and still got a lot to learn

Hi,
maybe someone could give me a hint. I installed everything and it looks like it is working, but no sensors are displayed in Domoticz. Any idea what's wrong?

I used this sensor before with a ESP Wifi gateway and it was working fine. The DallasTemp Sensors got visible in Domoticz right after the gateway was added in the Hardware section.

After installing the NRF24l01 on the Rasperry Pi 3 and follwing the instructions above, I added MySensorsGateway USB with /dev/ttyUSB20, but nothing happend.

Would be nice, if I could get this smart thing working. Else I would need to go back to the ESP Wifi gateway.

Domoticz log:
2016-12-30 00:31:01.610 Domoticz V3.5877 (c)2012-2016 GizMoCuz
2016-12-30 00:31:01.611 Build Hash: 15b013c, Date: 2016-11-10 16:44:33
2016-12-30 00:31:01.611 System: Raspberry Pi
2016-12-30 00:31:01.611 Startup Path: /home/pi/domoticz/
2016-12-30 00:31:02.327 Sunrise: 08:18:00 SunSet:15:59:00
2016-12-30 00:31:02.327 EventSystem: reset all events...
2016-12-30 00:31:02.411 Active notification subsystems: (0/12)
2016-12-30 00:31:02.448 WebServer(HTTP) started on address: :: with port 8080
2016-12-30 00:31:02.479 WebServer(SSL) started on address: :: with port 443
2016-12-30 00:31:02.481 Proxymanager started.
2016-12-30 00:31:02.516 Starting shared server on: :::6144
2016-12-30 00:31:02.516 TCPServer: shared server started...
2016-12-30 00:31:02.517 RxQueue: queue worker started...
2016-12-30 00:31:04.520 EventSystem: reset all events...
2016-12-30 00:31:04.520 EventSystem: reset all device statuses...
2016-12-30 00:31:04.521 EventSystem: Started
2016-12-30 00:31:05.519 MySensors: Using serial port: /dev/ttyUSB20
2016-12-30 00:33:06.145 Incoming connection from: 127.0.0.1

pi@raspberrypi:~ $ sudo /usr/local/sbin/PiGatewaySerial
Starting PiGatewaySerial...
Protocol version - 1.4
Created PTY '/dev/pts/2'
Gateway tty: /dev/ttyMySensorsGateway
================ SPI Configuration ================
CSN Pin = CE0 (PI Hardware Driven)
CE Pin = Custom GPIO25
Clock Speed = 8 Mhz
================ NRF Configuration ================
STATUS = 0x0e RX_DR=0 TX_DS=0 MAX_RT=0 RX_P_NO=7 TX_FULL=0
RX_ADDR_P0-1 = 0xa8a8e1fc02 0xa8a8e1fc00
RX_ADDR_P2-5 = 0xff 0xc4 0xc5 0xc6
TX_ADDR = 0xa8a8e1fc02
RX_PW_P0-6 = 0x20 0x20 0x20 0x00 0x00 0x00
EN_AA = 0x3b
EN_RXADDR = 0x06
RF_CH = 0x4c
RF_SETUP = 0x23
CONFIG = 0x0e
DYNPD/FEATURE = 0x3f 0x06
Data Rate = 250KBPS
Model = nRF24L01+
CRC Length = 16 bits
PA Power = PA_LOW
read: 2-2-0 s=255,c=3,t=24,pt=1,l=1:1
read: 2-2-255 s=255,c=3,t=7,pt=0,l=0:
send: 0-0-2-2 s=255,c=3,t=8,pt=1,l=1,st=ok:0
read: 2-2-255 s=255,c=3,t=7,pt=0,l=0:
send: 0-0-2-2 s=255,c=3,t=8,pt=1,l=1,st=ok:0
read: 2-2-255 s=255,c=3,t=7,pt=0,l=0:
send: 0-0-2-2 s=255,c=3,t=8,pt=1,l=1,st=ok:0
read: 2-2-0 s=255,c=3,t=24,pt=1,l=1:1
read: 2-2-255 s=255,c=3,t=7,pt=0,l=0:
send: 0-0-2-2 s=255,c=3,t=8,pt=1,l=1,st=ok:0
read: 2-2-0 s=255,c=3,t=24,pt=1,l=1:1
...

pi@raspberrypi:~ $ sudo cat /dev/ttyMySensorsGateway
0;0;3;0;14;Gateway startup complete.
2;255;3;0;24;1
2;255;3;0;24;1
2;255;3;0;24;1
2;255;3;0;24;1
2;255;3;0;24;1
1;255;3;0;24;1
2;255;3;0;24;1
1;255;3;0;24;1
2;255;3;0;24;1
1;255;3;0;24;1
2;255;3;0;24;1
1;255;3;0;24;1
2;255;3;0;24;1
2;255;3;0;24;1
2;255;3;0;24;1
...

Traces from sensor node:
Starting sensor (RNNNA-, 2.0.0)
TSM:INIT
TSM:RADIO:OK
TSP:ASSIGNID:OK (ID=2)
TSM:FPAR
TSP:MSG:SEND 2-2-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
TSP:MSG:READ 0-0-2 s=255,c=3,t=8,pt=1,l=1,sg=0:0
TSP:MSG:FPAR RES (ID=0, dist=0)
TSP:MSG:PAR OK (ID=0, dist=1)
TSM:FPAR:OK
TSM:ID
TSM:CHKID:OK (ID=2)
TSM:UPL
TSP:PING:SEND (dest=0)
TSP:MSG:SEND 2-2-0-0 s=255,c=3,t=24,pt=1,l=1,sg=0,ft=0,st=ok:1
TSP:CHKUPL:FAIL (hops=255)
!TSM:UPL:FAIL
TSM:FPAR
TSP:MSG:SEND 2-2-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
TSM:FPAR
TSP:MSG:SEND 2-2-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
TSP:MSG:READ 0-0-2 s=255,c=3,t=8,pt=1,l=1,sg=0:0
TSP:MSG:FPAR RES (ID=0, dist=0)
TSP:MSG:PAR OK (ID=0, dist=1)
TSM:FPAR:OK
TSM:ID
TSM:CHKID:OK (ID=2)
TSM:UPL
TSP:PING:SEND (dest=0)
TSP:MSG:SEND 2-2-0-0 s=255,c=3,t=24,pt=1,l=1,sg=0,ft=0,st=ok:1
TSP:CHKUPL:FAIL (hops=255)
!TSM:UPL:FAIL
TSM:FPAR
TSP:MSG:SEND 2-2-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
TSP:MSG:READ 0-0-2 s=255,c=3,t=8,pt=1,l=1,sg=0:0
TSP:MSG:FPAR RES (ID=0, dist=0)
TSP:MSG:PAR OK (ID=0, dist=1)
TSM:FPAR:OK
TSM:ID
TSM:CHKID:OK (ID=2)
TSM:UPL
TSP:PING:SEND (dest=0)
TSP:MSG:SEND 2-2-0-0 s=255,c=3,t=24,pt=1,l=1,sg=0,ft=0,st=ok:1
TSP:CHKUPL:FAIL (hops=255)
!TSM:UPL:FAIL
TSM:FPAR
TSP:MSG:SEND 2-2-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
TSP:MSG:READ 0-0-2 s=255,c=3,t=8,pt=1,l=1,sg=0:0
TSP:MSG:FPAR RES (ID=0, dist=0)
TSP:MSG:PAR OK (ID=0, dist=1)
TSM:FPAR:OK
TSM:ID
TSM:CHKID:OK (ID=2)
TSM:UPL
TSP:PING:SEND (dest=0)
TSP:MSG:SEND 2-2-0-0 s=255,c=3,t=24,pt=1,l=1,sg=0,ft=0,st=ok:1
TSP:CHKUPL:FAIL (hops=255)
!TSM:UPL:FAIL
....