RF transmission and FSK modules

[boban]

Hello,
I bought simple RF FSK transceiver / receiver modules. I was thinking, that I can connect the data to the PIN of PIC and simply transfer the data using SERIN / SEROUT. But this was actually wrong :) I read several posts here, how to make it work, but most of the posts are about ASK modules.
For FSK, I understood, that to send $55 bytes at the beginning doesn't have sense. But I understood, that my receiver module should have something like CD pin to detect, when it will start to receive the bytes. However, my module has nothing like this, just the DATA pin. Can anyone point me, how to simple transfer few bytes in the row via FSK without CD? Should I use some special encoding / decoding? I prefer to use serin / serout and not the pulse commands.

[Chris Barron]

Hello,
I bought simple RF FSK transceiver / receiver modules. I was thinking, that I can connect the data to the PIN of PIC and simply transfer the data using SERIN / SEROUT. But this was actually wrong :) I read several posts here, how to make it work, but most of the posts are about ASK modules.
For FSK, I understood, that to send $55 bytes at the beginning doesn't have sense. But I understood, that my receiver module should have something like CD pin to detect, when it will start to receive the bytes. However, my module has nothing like this, just the DATA pin. Can anyone point me, how to simple transfer few bytes in the row via FSK without CD? Should I use some special encoding / decoding? I prefer to use serin / serout and not the pulse commands.



There is a variety of modules out there, and they all work slightly differently. You don't say which modules you are using, but some need a level inverter to invert the signal (you should be able to negate this using the Picbasic serial modes) and some require there to be a pullup on the input.

I've used several radio modules over the years and TBH recent experience tells me that from now on I will be using Zigbee modules. I have been using Telegesis ETRX2 modules with the latest R3xx firmware and they're great ! They form a self healing mesh network and as long as your data overhead is low the inbuilt delivery security takes all the pain out of writing code which checks that the data has arrived. If you start to go too far out of range then you simply drop in another ETRX2 in the path and it acts as a repeater.

Although they aren't the cheapest solution at £11 each approx (UK), they are very good and can be controlled with simple AT commands.

One problem which I had was getting them to work in a different location to where they were first set up, and this was because they were set to stay on the original channel - when moved to a new location the local WiFi system was causing interference. Luckily they have a function which makes them search for the quietest channel before forming a network and then they can be set up to be reasonably immune to WiFi and other 2.4GHz signals

[Chris Barron]

I have been using Telegesis ETRX2 modules with the latest R3xx firmware and they're great !

I forgot to add, that as well as all the other benefits, the ETRX2 come with 16 digital I/O and 2 A/D inputs. The device can be set to wake up at a preset interval (measuring anything from seconds to hours) and transmit the state of the I/O pins as well as the A/D inut reading ( in the 0-1.2V range)

I use this feature in one of my designs to measure the output from a thermistor via a voltage divider and the unit therefor transmits a value relating to the temperature. The unit can be made to sit in a low power mode in between transmissions, and that means that a couple of AA batteries could last for a couple of years.

You can leave the remote unit powered up all the time of course, and then you send it a simple command to return the contents of the 'S-register' which carries all the information about the I/O pins. You are also able to SET and CLEAR the I/O pins remotely. This sort of functionality means that if your application is very simple, such as a remote control device, you are not required to use a host processor as yoiu are with conventional 433MHz modules


I bought a batch of older AM/FM/ASK/FSK 433MHz transmitters and receivers a long while ago and don't imagine ever using them, now that devices like the ETRX2 are available

[Ioannis]

Very interesting devices. Looks like the Digi's modules.

Have you made any range tests?

Which are you using the low pwer or the PA ones?

Ioannis

[Chris Barron]

Very interesting devices. Looks like the Digi's modules.

Have you made any range tests?

Which are you using the low pwer or the PA ones?

Ioannis

Yes they share some similarities with Digi's modules, and they're cheaper too. Telegesis offer plenty of support because these modules are in widespread use, one Swedish city has installed them in all electric meters for remote live billing applications, so I guessed they were reliable because of that !

Range depnds very much on the transmission path, the same as it does for any radio signal.
Being microwave devices (2.4GHz) they don't penetrate some materials as well as others but on the whole I think they compare favourably with the previous 433MHz modules I used (and they drew less power too)

My lab is in an upstairs room to the rear of the building. I put the main unit in there and walked down the street to the front of the house, about 35m before I started getting dropped packets. in the second test I put a third unit on the front lawn which immediately joined the network and acted as a relay station and then range went over 80m, line of sight.

These tests were all with the low power version. For the extra small cost the high power version would presumably give dramatically greater range, at the expense of power consumption.

[Ioannis]

OK. Thank. Digi has new devices for over 40Km range although these do not support the Zigbee stack.

Hope they will update the firmware.

I tried them and seems that this is true. Also powe can be adjusted for lower consumption.

Modules are small enough.

Ioannis

[Chris Barron]

OK. Thank. Digi has new devices for over 40Km range although these do not support the Zigbee stack.

Hope they will update the firmware.

I tried them and seems that this is true. Also powe can be adjusted for lower consumption.

Modules are small enough.

Ioannis


I know.

The project which got me into all this stuff was a remote machine monitoring project.
The ultimate hardware, for me, is the 6LowPAN protocol. Here, each node gets an IPV6 IP address and messages can therefore be routed to them directly via the internet without any translation.

Unfortunately, 6LowPAN implementations are thin on the ground, and I didin't get a large enough grant to buy the units from Sensinode which are the best application of 6LowPAN I've seen so far.

AVR (boo hiss) make a development board called a 'Raven' and there is a free RTOS and 6LowPAN implementation for use with those boards but then each node needs a Raven board.

[Ioannis]

IPv6 is very new to me. But having a lookat Sensinode site, made me think all stuff I used so far are ancient technology!

Very interesting devices.

Wish we had independancy from money and do all the things we dream.

I am in talks with a client to develop a network for banks so that they can control from the headquarters every stuff connected to the net. Many nodes may need wireless connections and zigbee seems a good idea.

If you feel like in discussing these projects I would be happy on private e-mails exchange.

Ioannis

[Chris Barron]

IPv6 is very new to me. But having a lookat Sensinode site, made me think all stuff I used so far are ancient technology!

Very interesting devices.

Wish we had independancy from money and do all the things we dream.

I am in talks with a client to develop a network for banks so that they can control from the headquarters every stuff connected to the net. Many nodes may need wireless connections and zigbee seems a good idea.

If you feel like in discussing these projects I would be happy on private e-mails exchange.

Ioannis

Ioannis, I might get in touch with you soon but other work is backing me up at the moment.

There are _a lot_ of private protocols, all designed with different uses in mind, and Zigbee is just one, and from what I hear is as much a money making system as it is a desire to build the best networking system.

For full industry standards compliance you should look at Dust Networks
http://www.dustnetworks.com/products/
Mesh wioreless networking with HART standards

They were recommended to me by an engineer who had implemented the wireless mesh system on oil rigs to provide roller bearing wear and vibration information. (The sensor is powered by a coil and magnet revolving within the bearing itself !)

Arch Rock seem to have started shipping their 6LowPAN solution, called Phynet
http://www.archrock.com/products/phynet_router.php
I would have tried to use it if it had of been released 6 months earlier, but not to worry !

Chris

[Ioannis]

Thanks for the links Chris. Seems that my weekend will be spent on reading!

Ioannis