uhf - receiver and or transmitter problems

#1
I'm not sure that I can be helped with the little info I can provide but here goes.

I found a data sheet on the web and hooked up the receiver and transmitter as it says or as best as I can figure!

There are four leds which are switching without the transmitter even being on, so I am now reading the values of 'serin 3,T2400,serdata' to the pc screen.

The immediate concern is why so many values change when the transmitter is off...or just transmitting a static number. I dont even think its working, could my wireless d-link be interfering?? Are bits of hookup wire acceptible antenna. The four leds flash a lot less when I hold the antenna.

I would really like to get this running , I can be much more specific if anyone can help.

the output is below and the receiver code---->

'Start CODE ,Radio Control - Receive

symbol serdata = b0

output 0
output 1
output 2
output 4

aloop:
serin 3,T2400,serdata
pins = serdata
pause 500
sertxd ("the value of b0 is --> ",#serdata,cr,lf)

goto aloop

'END CODE

THE OUTPUT
the value of b0 is --> 0
w?v?#?WW#?;vN##.????9#?253
the value of b0 is --> 0
w?v?#?WW#?;vN##.????9#?7
the value of b0 is --> 0
w?v?#?WW#?;vN##.????9#?49
w?v?#?WW#?;vN##.????9#?7
w?v?#?WW#?;vN##.????9#?27
the value of b0 is --> 48
w?v?#?WW#?;vN##.????9#?15
the value of b0 is --> 2
the value of b0 is --> 0
w?v?#?WW#?;vN##.????9#?7
w?v?#?WW#?;vN##.????9#?251
<----------

I have used receiver module RXB1 315/434 Mhz and its corresponding transmitter.
 

steliosm

Senior Member
#2
rigidigital you are probably having interference problems and I don't think it's coming from your d-link.
What you could do for a start is use a qualifier string before you transmit data and do the same on the receiver.
Your code should look like:
<code><pre><font size=2 face='Courier'>
Tx:
serout 2, T2400, (&quot;UUUUU&quot;, &quot;ABC&quot;, b2)

Rx:
serin 3,T2400, (&quot;ABC&quot;), b1
</font></pre></code>
 
#3
Stelios is right. To explain a bit more, the UUUU is 010101010101010 etc in binary and this moves the average to the midpoint so the receiver gets the data cleanly. The ABC is a qualifier so random data doesn't get through.

Start with this and it ought to work. If you end up sending long packets you need some way of making the number of 1's and 0's about equal but in practice picaxe packets are short and this is not a problem.

I have found that for small Tx units you need 5 U's and the higher power 1W ones need about 12 U's to stabilise.

Once you get one byte through, you will be hooked on RF!
 

manuka

Senior Member
#4
These preambles are certainly near essential I've also found, but VERY easy to arrange! Even with them you still may have strong local interference from wireless doorbells,garage door openers,weather stations etc, energy meters etc. These can near ruin your 433.92 MHz Picaxe datacomms...

Borrow a UHF scanner to check, or even make a simple general coverage 433 MHz receiver. I've many examples &amp; ideas =&gt; <A href='http://www.picaxe.orcon.net.nz ' Target=_Blank>External Web Link</a>, with even &quot;cotanga&quot; Yagi antenna. Stan
 

steliosm

Senior Member
#5
Some Rx modules have a Test pin (you need to check the datasheet). This pin gives you access to the signals received before they reach the Comparator block and come out in digital form through the normal Out pin.

You could try to <b>readadc </b> from that pin while your Tx module is off and have an idea if you have anyone close transmitting at this freq.

<code><pre><font size=2 face='Courier'>
'
' Sample the RF signals
' PicAxe 08M
' LED on pin 1
' ADC on pin 2
'
main:
' The main part
low 1
readadc 2, b0
if b0 &gt; 130 then goto echo_data
goto main

echo_data:
' Send the signal value to the PicAxe Terminal
high 1
sertxd (#b0)
low 1
goto main

</font></pre></code>

I used this code a lot when I had problems in order to find out what is happening.
If I run the code without an antenna attached to the module I get an ADC value 127. So, in order to make sure I have same actual transmition reading I have to compare the b0 value against eg. 130 and only send data for values above 130. Turning my Tx module on I had readings close to 200.
 
#6
thanks everyone. I will check as you suggest for a test pin on the receiver.

have used your code. The result so far is -&gt; ..it seems to be hanging on waiting for the &quot;ABC&quot; so no switching leds or output to screen.

I was a bit muddled about what actually happens to the &quot;UUUUU&quot; when sent or received so I tried with it and without. Same result. Seems to hang waiting for &quot;ABC&quot;.
But is good to learn how to get a remote to listen only to my instruction, thx again.

Im going to pull the transmitter picaxe of its proto board and wire it up on a breadboard. Could have some connection problem there maybe. Is there a way to test the transmitter ?
 
#8
Sounds like you are going to need a breadboard. First thing to check is to take the setup with the code as-is and take out the wireless Tx and Rx and see if the picaxes can talk to each other directly. Sometimes there is a silly mistake like N2400 on one and T2400 on the other.

Then if that works, it helps to hear what is out there. There is nothing special about the radio receivers, they are just audio receivers like an AM/FM radio. So all you need is an amplifier and a speaker and you can hear what is out there. You can quickly rig up an LM386, or get a pre built module or send the signal into the PC's soundcard line in.

Unless you have a ham radio operating next door there you should just hear a hiss.

Plan C is to get another Tx and Rx, just in case one has got zapped.
 

manuka

Senior Member
#9
These units work <b> brilliantly </b> on breadboards- check <A href='http://www.picaxe.orcon.net.nz/all3.jpg' Target=_Blank>External Web Link</a>
 
#10
This is pretty good right now. First I did the picaxe comm-check without the wireless.

Test was good. Next I pulled out the picaxe and refitted to a breadboard. Expecting not much @#. But it works . I have my ABC's transmitting at last.

Thanks for your walkthrough/tutorial, and ideas.

mick...

 
 

womai

Senior Member
#11
I played with such a 433 MHz TX/RX setup a few weeks ago and successfully managed to transmit data over the full length of a large breadboard :) Enrico Marconi and Heinrich Hertz would be impressed I guess. One of my goals was to investigate how long the preamble has to be.

A scope hooked up to the receiver indeed showed that the first data byte is messed up if there is no preamble at all, but looked clean even with a single &quot;U&quot; character as preamble. Interestingly, the receiver Picaxe only got consistently reliable data if there were around 3 - 5 preamble bytes (which about matches the number given in one of the previous posts for low-power TX/RX pairs).

I did not have much time to investigate this further (e.g. have a bit-by-bit look at the data stream), but I suspect after the rnadom bit noise of the first preamble byte the Picaxe may needs a byte or two before it can correctly identify the start bit and thus align itself correctly to the byte boundaries of the serial bit stream.

On the other hand, at least in my setup you can omit the preamble (and qualifier) of subsequent data bits if they get sent shortly after (within several millisec) of the first data packet. This can make for much higher usable data rate. (5 bytes of preamble and 3 - 4 bytes of qualifier to send a single data byte mean your usable data rate is only about 10% of the niminal baud rate).

Wolfgang

 

steliosm

Senior Member
#13
Most of the Tx/Rx modules are able to transmit digital data only due to their modulation type. Those modules have an On-Off Keying mechanism which means they only transmit if data pin is high and don't transmit when data pin is low.
On the other hand, you probably have up to 4.8kbs on the cheap modules, so you wont be able to transform music into digital signals and transmit those.

What you could probably do is have a Morse based intercom :)

Edited by - steliosm on 06/08/2007 10:54:30
 
#14
yes, that seems so.. I found this http://picaxe.orcon.net.nz/433txcw.bas I think it is sending morse 'tune' over the wireless.

Im opening a gate 1km away or more. (and over a hill)with the picaxe and 433 mhz wireless. Was hoping to get a DIY voice comms to go with it but I recon this is doubtfull. Found some 2.4 gig modules but range is only 300 feet. That would be 10 or more repeaters, cheaper to tape my mobile to the gate post .
 

steliosm

Senior Member
#15
That is a very interesting circuit and program.
I saw that he is using 10kbps modules. Maybe it could work with 4Kbps modules if the tone is changed.
Any ideas???
 
#16
There are two sorts of radio links out there - the expensive ones like zigbee are the ones that you put a High in one end and get a High out the other.

The small modules technically don't send highs and lows - they transmit AC signals. Thus they will work for voice and they will work for morse tones of various frequencies. What they actually transmit are changes in the voltage. So if you send a sine wave of 256Hz you get a sine wave out. But if you send a high or a low you get a click at the other end but nothing else.

If you make the Tx low and then suddenly make it high then the Rx will replicate this sudden transition. But if you send nothing else then the output drifts back to zero.

So, the first thing to do is set the Rx output somewhere in the middle so that if the next bit is a high or a low, it will be faithfully reproduced. This is the purpose of the &quot;U&quot; 01010101 preambles.

The other issue that comes up is the ratio of 1's and 0's. For long strings of data the ratio must be equal otherwise the output will drift. This can be done with Manchester coding or other coding systems, or even by sending bytes followed by their inverse eg 00000001 followed by 11111110, and discarding half the bytes. For short signal strings of a few bytes this isn't a problem, but the length of data strings when it becomes a problem is a bit unpredictable and depends on the type of data eg 00000001 is not a good byte to send as the ratio is 7:1, but ascii codes for numbers and letters tend to average out more evenly (ascii 48 to 122 are numbers and letters).

For sending a signal 1km, this is actually quite a technical challenge and I have been working on this for two years now. High power data is illegal on most channels. Some handheld CB radios seem to have the data channels unavailable. Many frequencies are already allocated (manuka has suggest ultra low RF frequencies down to tens of Khz where there are no rules). There are 1W 433Mhz modules available with ranges of several hundred metres, so it might not be 10 units to go 1Km but it will be 3 or 4. I'm working on a wireless repeater mesh with redundant nodes and multiple paths but I've been stuck on a reliable power supply solution for remote locations although it is almost ready for publication.

If you want to transmit audio, maybe just use a couple of cheap handheld UHF radios. At least audio is not illegal at 5W.

As an aside, maybe there is a way round the legal obstacle by sending speech with data encoded in it - at the simplest level short word could be a 0 and a long ramble could be a 1. Hmm, sorry about sending a long '1' here...

Edited by - Dr_Acula on 06/08/2007 15:16:17
 

manuka

Senior Member
#17
Mmm - &quot;Gidday mate&quot; = 1, while &quot;Hi&quot; = 0 ? Could make for slow data rates! Hams etc have of course used sub audible tone (100 Hz range <A href='http://www.popularwireless.com/codetable.html' Target=_Blank>External Web Link</a>)encoding (CTCSS)to switch VHF/UHF repeaters etc for years, &amp; I've pondered these may have some mileage for slow data work even on 477MHz UHF PRS CB. At least they wouldn't be heard by other channel users!

However DIY tones for data work are really pretty trivial as the weak signal robustness of DTMF makes this MUCH more appealing for slow data rates. Basic Stamps can generate DTMF ( sniff) but not so Picaxes, although I've some specialised ICs here (thanks to Brendan) awaiting a workout.

Stelios - I based that clever morse program on a '90s Basic Stamp offering,&amp; found it worked a treat with 08M for hidden transmitter hunting/ beacon work. As <A href='http://www.picaxe.orcon.net.nz/434tx.gif' Target=_Blank>External Web Link</a> shows,sending even 08M derived tones &amp; tunes is a piece of cake. Rather than sending speech as the gates open it may be better to send a jolly tune associated with the action - &quot;Walzing Matilda&quot; implies wide open spaces &amp; stock wandering to me!

As the good Dr-A correctly mentions,I'm still pondering &quot;DC band&quot; wireless links with both 27MHz &amp; ~72 MHz presently tempting. These bands have modest &quot;penetration&quot; &amp; antenna aren't too large. All manner of Aus/NZ regs need considering however,as do the boring issues relating to type approval,interference,repeater powering etc. Check the US FCC regs- -<A href='http://www.vantec.com/FCCregs1.htm' Target=_Blank>External Web Link</a> However it's still tempting to do more with 433MHz, perhaps using receiver preamps such the NEC UPC1688G. Even DSE handles these ( Z6011) The cheapo 433 MHz rx typically are only good to -100dBm sensitivity &amp; could easily have a 10-20 dB rx boost I'd say IF away from other 433 &quot;noise&quot;. As every 6dB gain equates to range doubling, them this could give ~ x4 the range?

EXTRA: Check the &quot;barebones&quot; 2 lead TX7433AM <A href='http://www.picaxe.orcon.net.nz/2wire433.jpg' Target=_Blank>External Web Link</a>being sold by Warwick Wireless (UK)=&gt;<A href='http://www.radiomodem.org.uk/#Lowcost ' Target=_Blank>External Web Link</a>! Range only modest but Picaxe applications abound. Stan




Edited by - manuka on 07/08/2007 03:00:43
 

steliosm

Senior Member
#18
Dr_Acule I've still have some concerns about the output of the receiver modules. The block diagram on the datasheet shows clearly that the signal travels through a comparator. So, I presume this will compare the voltage on order to output a TTL High on not. Then again, this could possible my module-dependent.
As for the 1km link that sounds very challenging. I've order a pair of 434Mhz 1Km range from eBay and I will do some tests to check the range my self, but this time away from the city n\and my Ham neighbors :)
 
#19
Hi Stelios - we may be talking about different types of modules. The ones I have used are audio and the quick test is to connect one to an audio amp and listen to the static.

A device that sends a high and the output is a high is a radio modem, and these usually work by sending tones of different frequencies and/or phases and the receiver has an RF to audio stage and then usually a phase locked loop and a voltage controlled oscillator and a comparator to read the voltage on the VCO. Does your block diagram have PLL or VCO anywhere?

Where did you get your ebay modules (which supplier) and do you have any specs? I'm very interested in anything that can go 1Km through trees and over a hill.
 

steliosm

Senior Member
#20
Yes, we are talking about different modules. Mine are only capable of transmitting at 2400bps and outputting TTL signals. Although they do let me check the signal coming in before is translated to TTL.

I got the new modules from this supplier: <A href='http://stores.ebay.co.uk/e-MadeinCHN' Target=_Blank>External Web Link</a>. This is the module:
<A href='http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&amp;item=290146864790&amp;ih=019&amp;category=115946&amp;ssPageName=STORE:pROMOBOX:NEWLIST#LIST' Target=_Blank>External Web Link</a>

1Km with LOS should be feasible in an area without noise. I'll be doing similar tests as soon as I get them in my hands. Will also be trying with different antennas design.

I will post any results and we could possible work something out.
 
#21
Thanks for that . I will do some work and see if i can come up with anything that might help.
I will be visiting some places to annoy and ask questions, last ime i did that i bought them lunch :)crocodile technology. For the antenna, are there petter ones, like a wok, and maybe antemnna kits that boost the signal ?
 
#22
ummm, I posted without realizing there were other posts !!! and my reference to crocodile has nothing to do with anything (i was just reading what it was about). Typing while looking at two different screens.:0)

I thought i would share that I went to electronics companies and back to the gate remote company that installed it in the first place (current range of the remote is 200 meters roughly)
and explained my needs to open this gate and communicate from the house 1km. Finally it was going to be done for $800.
However they never showed! It has prompted me to get interested in electronics :), whether or not the gate ever opens , im fining these resistors, diodes , npn's pnp's etc not to mention picaxe a great area of interest!
 

manuka

Senior Member
#23
Rigidigital- way to go! Electronics these days is very much a learn by doing field, although that esteemed &quot;Crocodile Clips&quot; simulator you mention can work mind expanding wonders. Sniff- wish it had been available when I was a kid...

433 MHz antenna are a breeze, since the wavelength (~70cm) makes things very doable as &quot;plumbers delights&quot;. Forget woks ( the 433 MHz wavelength is too large,&amp; go for Yagis. My dead simple so called &quot;cotanga&quot; <A href='http://www.picaxe.orcon.net.nz/yagi433.jpg' Target=_Blank>External Web Link</a>, even when unmatched, yields ~6dB gain that'll hence double ranges. One at each end will x4 the point to point range.

Stelios- I find that tx unit of yours is being sold by other Ebay outlets too, with ranges quoted to just 100m. Although it has 20mW (ISM max. is 25mW)output,such a LOS range as 1km will just not be feasible IMHO unless you use elevated antenna. You don't even need much of an amp on one of these cheap 433 rx units to hear 433 MHz band activity by the way either. I recall just an NPN into a piezo sounder gave an output that even my weary ears could hear. Stan

Extra: Have just got some prices from Warwick Wireless, who quote that 2 terminal TX7433 transmitter I'd mentioned above at ~UK &#163;7 + VAT. The usual 4 lead types sell here in NZ for a fraction of that,so it looks a non starter after all.



Edited by - manuka on 08/08/2007 00:19:25
 

steliosm

Senior Member
#25
Stan, do you have any links from the other eBay stores? This is the link to the PDF DataSheet I was given: <A href='http://www.e-madeinchn.com/TM1000-1S.pdf' Target=_Blank>External Web Link</a>.

The modules I currently use are rated to 10mW (10dbm). So, moving to 20mW it should be better. Your antenna is top in my list of things to try out with the new modules. 6dbi is a very good gain. Maybe with a 50Ohms cable I can get better results.
 
#26
Stelios - look at the other modules sold by e-madeinchn as there are some higher power ones. I am using their highest power modules which draw 100mA at 9V so must be up to a watt in power. They still only go 300m in the real world of trees and hills, though I did get 500m with 7 element yagis through trees. I've found though that building yagis takes time and I'm going back to omni 1/4 wave whips with multiple repeaters. Tests are continuing - I think I now have a reliable remote solar power system &lt;$20 (using circuitry borrowed from solar garden lights).
 

manuka

Senior Member
#27
It's worth pointing out that these 433 MHz ISM units also work as simple (non data) tx &amp; rx. Given the grief serial data alone may involve it's worth hence knocking up a &quot;walkabout pair&quot; for simple site survey,local interference checking &amp; antenna trials- especially since not everyone has a UHF scanner to listen to 433.92 MHz signals. Breadboarding these also allows swap outs to see which types are the most powerful &amp; sensitive. I've tested a LOT <A href='http://www.picaxe.orcon.net.nz/433rxtx.jpg' Target=_Blank>External Web Link</a>&amp; find the Oz. Jaycar units (as shown below) the best for the price.See my offerings-

(rx) =&gt;schematic <A href='http://www.picaxe.orcon.net.nz/433rxtones.gif' Target=_Blank>External Web Link</a> and layout <A href='http://www.picaxe.orcon.net.nz/433rxtones.jpg ' Target=_Blank>External Web Link</a>

(tx) =&gt;schematic <A href='http://www.picaxe.orcon.net.nz/433txtones.gif ' Target=_Blank>External Web Link</a> and layout <A href='http://www.picaxe.orcon.net.nz/433txtones.jpg ' Target=_Blank>External Web Link</a>

Stan

EXTRA: I even heard some local 2 way audio while out &amp; about recently doing a range test. This may have been from a wireless intercom or the like in a cafe/bar,&amp; was ~433.920 MHz on my scanner. In fact I recall LPD (Low Power Device) transceivers once were on sale in Australia (at least) before much more powerful 470 MHz UHF PRS CB kicked in. Just one more interference source? Nah-think positively ! A Google shows LPD 10mW sets are popular in mainland Europe (France &amp; Russia espec.). Such sets can come with 69 channels between 433.0750 and 434.7500 MHz,&amp; although just 10 mW output have ranges ~1km. Obviously hence their receivers are superb, so maybe hack one for data work? The data sheet of a Minicom =&gt; <A href='http://www.president-electronics.com/boutique_us/fiche_produit.cfm?type=4&amp;ref=minicom-2&amp;code_lg=lg_us&amp;pag=1&amp;num=2 ' Target=_Blank>External Web Link</a> indicates 0.2&#181;V sensitivity for a 20 dB S/N ratio. <b> This is ~10 times better than most cheapie &quot;garage door&quot; 433.92 receivers ! </b> . Anyone in Europe know the prices of these LPD sets? Care to send a few down under?


Edited by - manuka on 09/08/2007 12:02:56
 
#28
I absolutely agree that a mobile test box is worth having. My experience is that one can hear the tones much further than the range for detecting data - at least twice as far. The first test is to go for a walk and see how long a Serin works. Then I go searching round at about that distance looking for dead spots to find the maximum reliable distance in all directions.

I've been curious as to how the data fails - certainly looking at a cro trace with a Tx at maxiumum range the waveform gets quite distorted. It may be possible to use filters and tones of different frequencies to encode data but I have not found they add much in terms of range.

The idea of a preamp could be worth looking at.

Am running diagnostic tests at the moment on a remote repeater unit - will it work with worst case of 5 days of mist and clouds etc.
 

manuka

Senior Member
#29
A TV grade mast head preamp may be worth quick trials. Naturally this will also amplify THE NOISE, but in a quiet region such as your SA gumlands it may be viable. Borrow something from DSE ?
 
#30
I WAS LOOKING AT SOME 27 mHZ TRANCEIVER CHIPS. tHEY STATE THE RANGE IS UP TO 5 MILES FOR SOME. bUT THIS TECHNOLOGY MAY BE SOMETHING ELSE ENTIRLY TO GET STARTED IN ?

Product Name:
27 to 930 MHz FSK/FM/ASK Transceiver

Product Model/Number:
TH71221

Product Description:
The TH71221 is a single chip FSK/FM/ASK transceiver IC. It is designed to operate in low-power multi-channel programmable or single-channel stand-alone, half-duplex data transmission systems. It can be used for ISM, SRD or any other application operating in the frequency ranging of 300 MHz to 930 MHz. In programmable user mode, the transceiver can operate down to 27 MHz by employing an external VCO varactor diode.
 

manuka

Senior Member
#31
Good find! Those Melexis TH71221 &quot;DC to light&quot; chips are certainly something, with tempting prices (~US$5-10 it seems). Haven't checked them in detail enough to locate &quot;fish hooks&quot; however.

What I have done is look around for more sensitive 433.92 MHz offerings at good prices. Since the transmitter (Tx) power is legally only 10-25 mW &amp; companion receivers (Rx)are usually pretty deaf (beside a UHF scanner),it's tempting to push receiver specs. In theory UHF receiver sensitivity can be pretty keen, since band nose is very low at these freqs (that's if away from the usual urban 433.92 MHZ &quot;RF soup&quot; of course!). Expressing common ratings (most sensitive at top)gives - <code><pre><font size=2 face='Courier'>

dBm &#181;V
-120 0.224 Typical UHF scanner/LPD radio
-115 0.398
-110 0.707
-105 1.257
-100 2.237 Typical 433.92Mhz data Rx
- 95 3.976 </font></pre></code>
There's a fuller SINAD discussion at <A href='http://repeater-builder.com/measuring-sensitivity/measuring-sensitivity.html' Target=_Blank>External Web Link</a>


Googling the quest unearthed the likes of a Texan model rocket crowd <A href='http://www.privatedata.com/byb/rocketry/rocket_electronics/ ' Target=_Blank>External Web Link</a> who are using 433.92 MHz tracking beacons to locate their darlings after descents into tobacco patches &amp; cornfields. These guys often have to do ground level (or even sub ground should the 'chute fail !) tracking over several km, so are particularly keen on receiver performance, as a more powerful beacon transmitter would rapidly flatten it's battery (or require a bigger one to be launched aloft).They especially favour the <b> Wen Shing (Taiwanese) RWS-434-4 </b> &amp; <b>RWS-436-4 </b> <A href='http://www.texnet.net/ccent/rockets/txrx/rec%20comparisons.htm ' Target=_Blank>External Web Link</a> which have Rx sensitivity ~ -116 dBm = ~an order of magnitude better than Jaycar etc offerings! Prices ~US $7.95 from Canadian supplier QualityKits <A href='http://store.qkits.com/moreinfo.cfm/RX433C' Target=_Blank>External Web Link</a>

Anyone had experiences with these (or similar modestly priced) offerings? I've used more up market 433.92 MHz Tx/Rx (ChipCon-now owned by TI-<A href='http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&amp;familyId=935&amp;uiTemplateId=NODE_STRY_PGE_T ' Target=_Blank>External Web Link</a> etc) but prices, or 1000 up order needs, rather daunt... Stan

EXTRA: Maybe it's time to consider the 433.92 MHz spectrum as capable of finer use, as it strictly covers 433.075 - 434.775 MHz &amp; just blasting a single mid band signal is akin to wasteful RF pollution. Cheapie 433.92 MHz offerings are certainly fun,but really now are &quot;first generation&quot; &amp; maybe the likes of Radiometrix's <A href='http://www.radiometrix.co.uk/products/product1.htm ' Target=_Blank>External Web Link</a>should be considered as more state of the art. The &quot;hi power&quot; (gasp-25 mW !)Radiometrix TX2H <A href='http://www.radiometrix.co.uk/products/tx2h.htm ' Target=_Blank>External Web Link</a> shows the way, as with even just 2 channels (LPD transceivers have 69 @ 25 kHz spacings) duplex data or error correcting links could evolve. Dr-Acula will approve,as the TX2H conforms to Australian/New Zealand AS/NZS 4268:2003 &amp; they're even stocked in Oz. <A href='http://www.rfmodules.com.au ' Target=_Blank>External Web Link</a>. Mmm-any idea on costs?



Edited by - manuka on 12/08/2007 01:59:06
 

manuka

Senior Member
#32
3 days later. I've had multiple friendly emails with Radiometrix,but still have not been able to coerce them into revealing the costs of their 433 MHz darlings. Grr! Such tactics normally imply corporate level USAF style hammer/toilet seat pricing may be eventually expected...

Does anyone have inside knowledge on the price bracket their sensitive &amp; &quot;powerful&quot; devices are going for?

As mentioned above,I'm trying to work up a 2nd generation 433.92MHz wireless data approach, &amp; view sensitive NBFM (narrow band FM)devices as more tempting for &quot;surgical&quot; links rather than the present shotgun approach we all know so well. Ever the DIY skinflint, <b> I'd still like to hear of any cheap but sensitive 433.92MHz LPD hand held 69 ch. transceivers on sale in mainland Europe as well,with a view to importing a pair to NZ. </b> Anyone?

Footnote: Both NZ/Oz have near endless el cheapo &#189;W 38-40 channel 470 MHz UHF CB sets on sale,at prices as low as US$15-20 each. Strict &quot;3 seconds an hour&quot; regs. apply to the 2 designated data channels however. Stan
 
#33
If Sir needs to ask the price, then Sir may not be able to afford the exclusive products...

Why do companies do this? I found this out the hard way when I was 10, and on principle I never buy from stores that don't advertise the price. (I'm sure their modules are great).

Experiments continue with the self contained repeater modules. The RF bit turns out to be easy - it is the solar power supply that is more complicated. It is easy to trickle charge, and easy to overcharge (and then the customer wonders why the batteries die prematurely), but it is more complex to charge batteries the way they want to be charged within the constraints of solar power. Fortunately, picaxes are just perfect for this application. Am datalogging today.

Re the cheapo 1/2 W handheld units, we took some on a road trip recently to keep in touch between two cars. Firstly, they struggled to go more than 500 metres from inside one car to inside another. And secondly, the speech was almost unintelligable.
 

manuka

Senior Member
#34
Dr_Acula: Maybe backseat &quot;kid noise&quot; a factor ?! I've used Jaycar/DSE sets myself when convoy traveling to good effect here in NZ, &amp; LOS have often made car to care links of 10km (across water). Interestingly,unlike cell phones,it's apparently NOT illegal to use 2 way radios in many counties while driving!

Some kind soul has just pointed me to a UK PMR transceiver mods site that allows 433.92 MHz LPD coverage <A href='http://www.delboys446.co.uk ' Target=_Blank>External Web Link</a> with cheapo &quot;20 quid a pair&quot; Telcom TE-100/150 (Tsuen Shing NLM-8CI variants)etc.

Mmm- should be legal for 10mW data work OK, so may order a few directly hence,unless a used pair is cluttering someones life &amp; they care to send them down under in return for all that NZ lamb we sent Blighty during the war. Stan
 

manuka

Senior Member
#35
<b>Dr-Acula </b> :(again- 2nd opinion!). What is the sensitivity of the receiver modules you're using? As mentioned above most &quot;cooking versions&quot; are pretty mediocre &amp; better ones (~US$8-10) will have a much improved reception range. Every 6dB gain = range doubling of course,so 12db =double x double = x4 the range. This of course in your case means fewer repeaters. Stan
 
#36
Manuka - I called rfmodules.com.au, to get a price on the BIM1-151 ,Power 100mW ,Range 5km Modules(Tranceivers). They are $89.00.
Not much of a guide , however, yep they could all be pricey little fellas :)
 
#37
I'm not sure how to measure the sensitivity. I guess one has to weigh up the expensive sensitive modules ($89) and the cheap ones that are not so good ($4). I'm working on getting the repeater modules as cheap as possible (one AA battery, 4 solar cells etc), so then one can afford lots of them!
 
#38
I am trying to send a 9 digit number. No luck yet. Ive tried sending 3 * 8 bit to get the number but it gets jumbled.

Could you give an example of sending long string, or manchester coding ? The Rx is receiving from a couple of sources at once so I need to get the numbers in one go if possible ??
 
#39
If someone has time to translate this into PICAXE code then here is Manchester and CRC:
<code><pre><font size=2 face='Courier'>
Encode:
EncodedWord = 0
Clear ENCODER_LOOP
Repeat
EncodedWord = EncodedWord &lt;&lt; 2
EncodedWord.0 = 1 ' Default to Bit = 1
EncodedWord.1 = 0
If TempVar.0 = 0 Then
EncodedWord.0 = 0 ' Bit = 0
EncodedWord.1 = 1
EndIf
TempVar = TempVar &gt;&gt; 1
Inc ENCODER_LOOP
Until ENCODER_LOOP &gt; 7
Return

Decode:
Clear ENCODER_LOOP
Clear ERROR_FLAG
Repeat
TempVar = TempVar &lt;&lt; 1
If EncodedWord.0 = 0 Then If EncodedWord.1 = 1 Then TempVar.0 = 0 ' bit = 0
If EncodedWord.0 = 1 Then If EncodedWord.1 = 0 Then TempVar.0 = 1 ' bit = 1
If EncodedWord.0 = 0 Then If EncodedWord.1 = 0 Then Set ERROR_FLAG ' error in bit decode
If EncodedWord.0 = 1 Then If EncodedWord.1 = 1 Then Set ERROR_FLAG ' error in bit decode
EncodedWord = EncodedWord &gt;&gt; 2
Inc ENCODER_LOOP
Until ENCODER_LOOP &gt; 7
Return

CRC:
CRC_OUT = (CRC_IN * 256) ^ CRC_OUT
Clear CRC_LOOP
Repeat
rol CRC_OUT , Clear
If STATUS.0 = 1 Then
CRC_OUT = CRC_OUT ^ CRCPolynomial
EndIf
Inc CRC_LOOP
Until CRC_LOOP &gt; 7
Return
</font></pre></code>
 
#40
Is the size of data sent/received, more a function of the rf modules than the picaxe ?
Would it be pretty easy to send a 16 bit number with different module ?
 
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