[chbot] nordic nRF

[Mark Atherton]

Hi Volker,

* procurement:*

The smaller RX unit being passed around was the nRF24LE1, which has 
the 8051 as well as wireless on-chip. The PCB had a small etched 
antenna. This used 2mm headers which are a pain, and came from 
<http://stores.ebay.com.hk/worldwindow2010>http://stores.ebay.com.hk/worldwindow2010

The larger TX unit, with MIDI over USB has a dsPIC33EPxxx (older 
version of 
<http://www.ebay.com/itm/181143989109>http://www.ebay.com/itm/181143989109) 
controlling an nRF24L01+, and an external RP-SMA antenna. This was 
<https://www.sparkfun.com/products/705>https://www.sparkfun.com/products/705

If I were to do it all over again I would only buy from 
<http://www.canton-electronics.com/>http://www.canton-electronics.com/ 
who also have the nRF24LE1 programmer along with low cost modules on 
0.1" headers.

All of these suppliers seemed pretty good, Canton was the cheap and 
easy to deal with.

On the FPGA based Audio-Box (brought it to other meetings) it is the 
reason for the wireless MIDI. It uses the Sparkfun module attached to 
a NIOS II 32 bit soft core processor. This CPU also drives the real 
time video rendering engine along with audio control gain structure 
and associated housekeeping.

* RF *

TX power is adjustable from 0dB downwards. At 250kb/s RX sensitivity 
is -94dBm. Allowing for 12dB real world loss gives about an 82dB link 
budget. This is about 100 metres of line of sight range at 2.4GHz 
(much less indoors). Modules are tunable from 2400 to 2515MHz in 1MHz 
steps, so easy to get away from WiFi etc.

Modules can be run up in CW mode - TX power was close to 0dBm, and 
freq error was set by tolerance of the 16MHz xtal.

* software *

The Nordic SDK is targeted at the Keil 8051 tool-chain, of which the 
latest free version is limited to 2k code size. There was a free key 
to open this up to 4k, but does not seem to work with the latest 
version. SDCC is open and free. Not the highest level of 
optimization, but the price is right and easy to use. The only thing 
that drove me nuts was having to put all of the interrupt handlers in 
the main module.

Some kind soul has created an SDK 
http://www.diyembedded.com/lib/nrf24le1/nrf24le1_sdk_v1.0.zip he has 
been a bit enthusiastic with level of abstraction and given the 
bare-metal application I wanted, only the headers were used. My basic 
system is only a few hundred bytes, but I have also added a command 
line interface for debug which brings things up to a few k.

* embedded 8051 version *

Has sleep management so units can go into low power for long periods 
and only pop up with measurements as required - you can get average 
current down to a few uA.

Part also has ADC, PWM, UART, GPIO on board - the trick is to find a 
module with required features available.

* quick start *

I have a lot of stuff to help quick-start-you if any of this appeals, 
and some spare hardware.

Nordic also do a UHF version that covers 433 / 868 / 920MHz with 
+10dBm TX, but lower data rate. With good RF engineering, this could 
get you kilometres of range...

Regards,

Mark


At 12:20 a.m. 21/05/2013, you wrote:
>Mark,
>
>Those nordic RF link chips look interesting. You probably got the 
>details wrong a bit but hey. Only the receiver has an 8051. Did you 
>use their SDK or something else? Does one have to use the internal 
>8051? And at 20pin 4x4mm QFN, where did you buy your boards?
>
>Thanks, Volker