How abour SipHash? Output is only 8 bytes and:

It adds about 1200 bytes to the code size and uses about 42 bytes of RAM.

what about these:
http://www.aliexpress.com/store/product/Livolo-EU-Standard-Remote-Switch-Crystal-Glass-Panel-EU-standard-VL-C702R-11-Wall-Light-Remote/500715_513111555.html

they have some models with RF and there is a arduino library to control them with RF:
http://forum.arduino.cc/index.php?topic=153525.0

or you can try and make your own touch panel with cheap touch sensors inside...

Are you from an EU country? do you mean Low Voltage Directive? couldn't find anything like "does not require certification"...

@daulagari said:

Still a nice idea to make a full-duplex link. Do you have any special plans with it?

Main goal is speed and reliability.

Speed will allow better real-time interaction. When someone hits "lights on" button, they expect it to turn on instantly. Reliability, because they expect it to work every time!

I'm just trying to make the most out of these networks. Most of my nodes won't be battery powered, so the extra power consumption is not an issue. The same goes for the cost of an extra radio per node.

I'll do more tests regarding distance and orientation between radios.

Most of my tests were done connecting arduino and radios with jumper wires... so probably most of the time the radios were a few centimeters apart. This design with custom pcb has only a few days...

Now that you both mention possible interference between them, I did notice a reduction the maximum range, but not writing failures or other issues... when in range, all worked smoothly!

what you think minimum distance should be? if interference issue is solved, what you guys think about this?

I am surprised... What kind of distance is there between the two nodes?

about 5 meters with 1 wall between.

what do you think should be the minimum distance between them in order to avoid that kind of interference? any particular orientation between them that should be better?

I'm working on a sensor network (similar to MySensors) for Arduino Pro Mini and a RPi (using nrf24l01+ and a websockets gateway for a future web app).

When I found out about this site I already had invested a lot of my time doing this, but I relate myself a lot with this project.

Today I want to share my latest experience with full duplex networks. I'm using 2 nrf24l01+ radios for each node: one for writing (TX) and another to read (RX):

Level 0 Node : (0)      Radio1: RX, Channel A | Radio2: TX, Channel B
Level 1 Nodes: (1-5)    Radio1: RX, Channel B | Radio2: TX, Channel A
Level 2 Nodes: (n1-n5)  Radio1: RX, Channel A | Radio2: TX, Channel B

There are several (theoretical) advantages in using this:

• with 2 different channels the collision rate between messages is smaller.
• dedicated radios for RX and TX means no delay in switching between radio listening and writing.
• smaller delay/lag between action request and event occurrence .
• better overall speeds.
• better reliability(?)

I'm just starting to get my first results with this approach using only 2 nodes (for now). I'm using RF24 library from TMRh20 (thanks for the help! ) but I never got these kind of speeds [www.youtube.com/watch?v=mODflsK1Ab0], probably because of some differences in physical/environment conditions. I got lower speeds, so, instead of absolute values, I can claim around 50% increase in transfer rate speeds and even better improvement in round-trip time between 2 nodes.

I don't have a large network (yet) to verify improvements in a busy networks, but either way, it's not easy to assess the real benefits of a full-duplex network.

I would like to hear your feedback and suggestions about this... Do you think the benefits will be worth the extra radio or am I just wasting time on this? Is this something that may be considered in MySensors?

Here are some pictures of the my nodes with custom pcb for wiring both radios:

See also the rest of this thread, just a message digest is very likely not the best solution.

Of course not by itself... the idea was to use it to implement some kind of HMAC and combine it with a stream cipher or a vernam cipher.

How abour SipHash? Output is only 8 bytes and:

It adds about 1200 bytes to the code size and uses about 42 bytes of RAM.