PICAXE URF and ERF Modules

srnet

Senior Member
Good stuff. Good modules.

Easy to use, work out of the box, but a good deal of configuration options if you choose to use them.
 

Grogster

Senior Member
@ Technical - WOW. :eek:

These look great, and the ability to be able to wirelessly upgrade PICAXE code would save me lots of time removing screws to get to the pin headers on boards. Not that I had to do that very often - I have confidence in my code... ;) :D

I did not get around to ordering the ERF modules, so will get the PICAXE enabled set instead.

TechSupplies website mentions that the ERF modules(not the ERF/URF pair) are out of stock - any idea when they will have more?
 

Technical

Technical Support
Staff member
TechSupplies website mentions that the ERF modules(not the ERF/URF pair) are out of stock - any idea when they will have more?
We have limited stock at present so are initially only selling them in ERR/URF pairs. More stock will be available very soon and then individuals will also be available.
 

BeanieBots

Moderator
The Rev-Ed offering certainly looks like a good value offering compared to XBEE. The ability to use them for program download is a real bonus. Something I had a half hearted try with XBEE but gave up. (Does XBEE support break?).
Will more than likely add a set to my next order to have a play.
 

MFB

Senior Member
The documentation states that there is an option to use a ERR/URF operate at 433MHz, but at reduced range. Does anyone know what the percentage reduction in range could be expected when opeariting at 433MHz?

As the reduction is probably due to detuning of the on-board chip antenna, would it be possible to remove this and replace it with a socket for an external antenna?
 

MartinM57

Moderator
Looks like these ERFs/URFs need a thread of their own :)

If I buy a PICAXE-oriented ERF/URF pair, ie supports break signalling and inverts polarity, how do I reconfigure them to not invert (so I can use them elsewhere) and then, later, reconfigure them back to PICAXE-oriented?
 

Grogster

Senior Member
Looks like these ERFs/URFs need a thread of their own :)
Yes, they do - perhaps the moderators can split the thread?

If I buy a PICAXE-oriented ERF/URF pair, ie supports break signalling and inverts polarity, how do I reconfigure them to not invert (so I can use them elsewhere) and then, later, reconfigure them back to PICAXE-oriented?
I understand you can program them to be N or T with commands.
 

srnet

Senior Member
The documentation states that there is an option to use a ERR/URF operate at 433MHz, but at reduced range. Does anyone know what the percentage reduction in range could be expected when opeariting at 433MHz? As the reduction is probably due to detuning of the on-board chip antenna, would it be possible to remove this and replace it with a socket for an external antenna?
Answered here, first post, at least as it relates to the XRF.

http://www.picaxeforum.co.uk/showthread.php?21209-RFM22-versus-XRF

By comparison the 868Mhz RFM22 pair when operated at 434Mhz had about 1/10th the range of a 434Mhz RFM22 pair operated at 434Mhz.

This issue is likely more than just the antenna, transistor RF amplifiers have a characteristically low output impedance so these XRF and RFM devices will have a matching network for effective power transfer into a 50R cable or antenna. The matching networks are tuned to a band, so a matching network for a 868Mhz, is not going to use the same tuned components as one for 434Mhz.
 

Technical

Technical Support
Staff member
Looks like these ERFs/URFs need a thread of their own :)

If I buy a PICAXE-oriented ERF/URF pair, ie supports break signalling and inverts polarity, how do I reconfigure them to not invert (so I can use them elsewhere) and then, later, reconfigure them back to PICAXE-oriented?
It's a custom firmware, so there are various internal settings that are different and so simply inverting the pins by itself does not convert 'PICAXE ERF' to 'Normal ERF'. For instance with PICAXE version CTS pin is permanently fixed to be a 'Chip Enable' pin instead (to enable side by side use with the AXE027 cable).

The simplest way to do this is is to have 1 URF (universal) and one of each type of ERF. Or convert all your projects to use the N polarity!

The URF has no notion of polarity - the polarity is applied by the ERF at the far end. Likewise a normal and custom ERF can quite happily talk to each other, one using N9600 and the other T9600.
 
Last edited:

Goeytex

Senior Member
The documentation states that there is an option to use a ERR/URF operate at 433MHz, but at reduced range. Does anyone know what the percentage reduction in range could be expected when opeariting at 433MHz?

As the reduction is probably due to detuning of the on-board chip antenna, would it be possible to remove this and replace it with a socket for an external antenna?
Not only will the Antenna be mismatched, so will other components such as capacitors and inductors. Changing the antenna to 433 MHz will only help slightly. Consider that there is approximately a 3dBm loss at 915 MHz when the matching hardware is for 868MHz.

I would not even consider using one of these at 433MHz if the hardware is matched for 868Mhz. The range would be absolutely terrible.
 
Last edited:

MFB

Senior Member
So we don't really have an alternative to the basic 433MHz modules already offered by Rev-Ed. That's a pity because 433MHz is the band allocated for model aircraft telemetry and also use by the high altitude balloon community. Not a big market for sure but there would be other legal applications for a 433MHz version of the ERR/URF modules.
 

Goeytex

Senior Member
It wouldn't take much for Rev_Ed to have the Manufacturer change a few components on the board to have a Module optimized for 433 MHz. However, placing a 433 mhz chip antenna on the board may be an issue due to size. Yaego has one that might it. However if antenna size is an issue, they could leave the chip antenna off and just have a place for a wire or spring antenna .... or mount an SMA Connector.

But for Rev-Ed to suggest using this module at 433 Mhz is .... well .... not a very good idea. But , in defense, they did qualify that with "in the classroom" where the range is not likely to be more than a few meters, which probably is all it will get.

But it needs to be clearly understood that these modules are hardware optimized for 868 MHz and operating them at 433MHz or 315Mhz will give very poor results.
 
Last edited:

hippy

Technical Support
Staff member
It wouldn't take much for Rev_Ed to have the Manufacturer change a few components on the board to have a Module optimized for 433 MHz.
In theory it's possible but there may be technical issues as noted, cost and business issues in being worthwhile and delivering return on investment for the manufacturer. It might require a commitment to minimum order quantities so there'd have to be a business decision there.

That's neither a will or won't and I'll make sure the suggestion of an optimised for 433MHz module gets passed on.
 

srnet

Senior Member
But for Rev-Ed to suggest using this module at 433 Mhz is .... well .... not a very good idea
With the XRF modules (same RF IC) I was getting open air flat LOS of circa 220M at 1mW with the 868Mhz module used at 868Mhz.

As I noted in the RFM22\XRF comparision I did the range dropped to about half that when the 868Mhz module was used at 434Mhz, this would equate to an open air LOS of around 350M at 10mW, so the receivers are not that deaf.
 

Goeytex

Senior Member
With the XRF modules (same RF IC) I was getting open air flat LOS of circa 220M at 1mW with the 868Mhz module used at 868Mhz.

As I noted in the RFM22\XRF comparision I did the range dropped to about half that when the 868Mhz module was used at 434Mhz, this would equate to an open air LOS of around 350M at 10mW, so the receivers are not that deaf.
I recall you mentioning these unusual range figures. However I don't think you were using chip antennas which represent a loss ( .5 dBm gain) and I don't think you were sending multiple byte data packets. ( correct me if I am wrong). And I believe you were using an unusually low frequency deviation figure and an extremely low RF data rate.

So am am not confident that your results will relevantly correlate to these URF/ ERF modules. My guess is not, and that the only way to tell is to actually field test them.
 

srnet

Senior Member
And I believe you were using an unusually low frequency deviation figure and an extremely low RF data rate
That was the case for the RFM22.

The XRFs was being used out of the box, but configured for the lowest data rate that would work (38Kbps a firmware bug prevents the lower data rates being used).

And then the only change from the standard setup was to setup the frequency for 434.075Mhz.

The packets were a 6 byte numbered packet, so you could tell when the receiver started to loose packets.

So what was unusual about the XRF range figures ?
 

Goeytex

Senior Member
440 Meters @ 1mw? ( 0 dBm) ....

I'd say that is quite exceptional and therefore quite unusual. Id like to see those number replicated. Unfortunately, even with over 60 modules of various makes & models here I, do not have any XRF modules to play with.
 
Last edited:

manuka

Senior Member
Quite aside from the exciting URF/ERF technical features, 868MHz allows both a quieter band slot AND simple (but effective) dish style directive antenna. Parabolic dishes (~several wavelengths across) at lower UHF freqs are normally too large to be viable, but at higher subGHz frequencies even a wokfi approach may suit.

Little more that just placing the URF/ERF at the dish focal point may be needed to give a 10-15dB gain! As each 6dB gain is equiv to doubling range, then 12dB = x4, & 18dB = x8 etc, and I'd say an order of magnitude range boost may result with dish or corner reflectors at each end. Stan. (ZL2APS)
 

Attachments

Haku

Senior Member
That is great news, the Ciseco wireless modules are so easy to use. I've been wrapped up in so much other stuff the past few months I've barely had the chance to do any Picaxe stuff :( but now these new modules are out I'll have to create some time to get back to tinkering with my Picaxes and XRF units (and maybe get some of the new modules)

Not only will the Antenna be mismatched, so will other components such as capacitors and inductors. Changing the antenna to 433 MHz will only help slightly. Consider that there is approximately a 3dBm loss at 915 MHz when the matching hardware is for 868MHz.

I would not even consider using one of these at 433MHz if the hardware is matched for 868Mhz. The range would be absolutely terrible.
When I did my first range tests with my v1.3 XRF modules I managed to get nearly 600 meters at 315mhz with the appropriate length antennas, but there were a few trees & things in the way so the signal wasn't very reliable, but it managed it. That was at 1.2k over the air baud rate instead of the default 250k over the air rate.

BTW, if anyone's wondering why the over the air baud rate is so significant when you're trying to achieve long ranges, this is a quick vid I made a while ago showing the difference between 1.2k & 250k transmissions, I held a wireless signal detector next to an XRF:
http://www.youtube.com/watch?v=I5D97NgMhXA
 

srnet

Senior Member
BTW, if anyone's wondering why the over the air baud rate is so significant when you're trying to achieve long ranges, this is a quick vid I made a while ago showing the difference between 1.2k & 250k transmissions, I held a wireless signal detector next to an XRF:
http://www.youtube.com/watch?v=I5D97NgMhXA
Yes, in general that is true, lower data rate more range.

However when I was testing the XRF as a contender for the satellite, I discovered that a firmware bug was preventing the 1.2K from working. The view from Ciesco support was that due to the various optimizations used in setting up the RF chip, there may not be much real world difference in performance between the 38K and 1.2K rates.

Its something I need to look at in more detail for the RFM22, most of the long distance LOS testing (8.4km at 12mW) has been done at 1kbps, but obviously if I can get much the same distance at 2k or 5k then the amount of battery power used to transmit a packet is significantly reduced.
 

MFB

Senior Member
Manuka, good tip about increasing range with a pair of directional dishes but I fear that this would not be legal for a transmitter operating in the UK.
 

Paix

Senior Member
@MFB, but, if the link is one way, then there is no impediment to improving the receive leg with a directional antenna.

6dB to 9dB gain should be realisable.
 

manuka

Senior Member
Goeytex/srnet: 1mW at even 433 MHz will readily cover many 100s of metres LOS (line of sight) distances with a sensitive receiver. Some years back we managed 3km across water with 2.4GHz 1mW XBee modules & simple mesh WokFi dishes (here 350mm diameter = ~3 wavelengths at 2.4GHz) - refer pix below showing the departing test crew.

MFB: Antenna restrictions may not be an issue if the transmitter's e.i.r.p limit is respected-refer typical "900 MHz band" usage (sourced via NZ's RSM site -2004) . This sub GHz RF spectrum space may offer greater e.i.r.p. than the 10/25 mW at 433 MHz too, with some regions allowing 500mW or more. However the regs. are VERY involved,with the likes of even Tx duty cycle important.

Australia & NZ spectrum regs are normally identical, but differ significantly in this "900MHz" band. I'm still at the Sunday morning first coffee stage, so even these local regs. are a tad mind numbing...

Extra: (2nd coffee!) At ~900MHz a wavelength is ~300mm, so reflectors can be just ~600mm across (a couple of wavelengths), & quite compact antenna become viable. Solid reflective surfaces are not even needed, & for wind & weight reduction just bars spaced ~1/10 wavelength (~30mm at 900 MHz) will suffice. Mesh or a couple of oven/BBQ racks may even do nicely. Antennamagus has zillions of ideas.

Corner reflectors are well suited to quick trials & can be made VERY simply - foil lined cardboard box etc. A South African cellular modem setup (below) claimed a 10-12dB gain. As such signal enhancers can occur accidentally (due to nearby reflective hardware or room walls & corners etc) it'd be difficult to criticize simple placement of ERF/URF at the sweet spot of such setups.

Stan. (Radio ham ZL2APS, & 50 years an antenna wrangler)
 

Attachments

Last edited:

Goeytex

Senior Member
Am I correct to understand that with these modules only two possible frequencies can be selected within the 915 ISM band .... 903MHz and 915 Mhz?
 

srnet

Senior Member
Am I correct to understand that with these modules only two possible frequencies can be selected within the 915 ISM band .... 903MHz and 915 Mhz?
The general process is, setting to 434.075Mhz in this case;

Set the channel ATCH4 '433.5Mhz

Set the channel spacing ATCS25 '25khz

Set the channel number ATCN23 'set channel number 23, (433.5 + (23*.025)) = 434.075Mhz

Don't see why the same process would not apply to the 903 and 915 channels.
 

Technical

Technical Support
Staff member
srnet is correct, set the nearest 'main' frequency then tweak via the channel number (and spacing).
 

BeanieBots

Moderator
and mine have already arrived in the post!
However, I'm having difficulty finding information about how to 'fiddle'.
Is there a datasheet for AT commands etc?
 

Technical

Technical Support
Staff member
and mine have already arrived in the post!
However, I'm having difficulty finding information about how to 'fiddle'.
Is there a datasheet for AT commands etc?
PICAXE ERF/URF are supplied ready to use, so no AT setup is required at all for the majority of users.


However we're working on a simple wizard to add to PE that will do common AT tasks 'automatically' for you (e.g. change freq) and that will be available shortly, along with an AT command summary.
However all XRF/ERF/URF share the same AT commands, so you can also take a look here
http://openmicros.org/index.php/articles/84-xrf-basics/114-xrf-at-command-reference
Note the precise timing of +++ sequence and the 5 second AT mode timeout.

To change AT commands on a URF you need to open a serial terminal session at 9600 baud and send ascii codes for the AT commands.
To change AT commands on a ERF the easiest way is to write a PICAXE program to do the AT command sequence for you (serout/in at N9600).
 

BeanieBots

Moderator
Thanks srnet & Technical, that's exactly what I was after.
An addition to the PE for doing the common tasks would be most welcome. I've tried it with XBEEs using a terminal emulator and it can get quite frustrating! Something like the existing XBEE-setup wizard would help a great deal.
Meanwhile, is there anything like X-CTU available?
 

Haku

Senior Member
To change AT commands on a ERF the easiest way is to write a PICAXE program to do the AT command sequence for you (serout/in at N9600).
I have found that with my 6 XRF's it became difficult to remember what AT commands I had set on each module, so I put default settings on all of them and I get the Picaxe to send the AT commands to the module upon bootup, making it much easier to keep a handle on things. It also means the Picaxe checks to see if the module is connected and working.

Code:
#picaxe 18m2
#no_data

setfreq m16

symbol XRFinput=b.6     'input line of XRF/ERF
symbol XRFoutput=b.1    'output line of XRF/ERF
symbol XRFbaud=T9600_16 'baud rate setting of XRF/ERF
symbol XRFok=b2         '0=timeout from XRF/ERF
                        '1=OK
                        '2=ERR
symbol temp1=b3
symbol temp2=b4

'Put XRF/ERF into AT command control and configure it
high XRFinput
pause 4400  'pause 1.1 seconds
serout XRFinput,XRFbaud,("+++")
pause 4400  'pause 1.1 seconds
serout XRFinput,XRFbaud,("AT",cr)
gosub checkXRFok
if XRFok=0 then:sertxd("XRF/ERF timed out"):endif
if XRFok=1 then:sertxd("XRF/ERF responded OK"):endif
if XRFok=2 then:sertxd("XRF/ERF responded with ERR"):endif
'Put XRF/ERF into default settings
serout XRFinput,XRFbaud,("ATRE",cr)
'You can insert your own AT command settings here
'Exit from AT command mode
serout XRFinput,XRFbaud,("ATDN",cr)



'Main code goes here



checkXRFok: 'Check response from an issued AT command
 serin [800],XRFoutput,XRFbaud,temp1,temp2
 XRFok=0
 if temp1="O" and temp2="K" then:XRFok=1:endif
 if temp1="E" and temp2="R" then:XRFok=2:endif
 return
Should be very easy to modify for your own needs (baudrate, IO pin connections etc.)
 

BeanieBots

Moderator
https://github.com/CisecoPlc/XCM-for-Windows
http://www.ciseco.co.uk/downloads/XCM/install.htm
Couldn't get much sense out of either of those links. Maybe I'm missing something?
The first just brings up a page of html code but no install.

The second link kindly provides the source code but it requires visual studio 8 which I don't have on this machine and I've long ago given up trying to get visual studio 10 to run under windows 7 (come back WinXP & VB6, all is forgiven!).

Never mind. It's not something I'll lose too much sleep over. As suggested by Technical, nothing a few lines of PICAXE code won't cure (thanks Haku for a good example) while I wait for the PE wizard.
 
Top