RF Transmitter/Reciver

[Fredrick]

Have anyone here used Parallax RF transmitter and reciver?
Does it work well?

I look´s like there is no problem to use those with PBP! or??

The manual says upp to 150 meters, is that true or is the actual distans shorter?

http://www.parallax.com/Store/Access...%2cProductName

[mackrackit]

IF you are going to use this type of RF, buy them here:
http://www.rentron.com/PicBasic/RemoteControl.htm
They work very well and the range is as advertised.

Bruce at rentron is one of the major contributors to this forum.

[Fredrick]

Can´t find the parallax RF moduls on www.renton.com...

[mackrackit]

On the left side of the screen in the link I gave. They are not parallax, but are made with the same Linx module.

[Fredrick]

Can i use one transmitter to send the temperature from an DS18S20 to 3 recivers?

[mackrackit]

Yep, as long as they are all the same frequency.

[Fredrick]

Whats the diffrents between 315MHz, 418MHz, 433MHz modul? Only the MHz or has it to do whit other things?

To write a program to those modules i use SEROUT and just send a text and recive it whit SERIN?

[Acetronics2]

Hi,

The answer is quite simple :

Some frequencies are allowed in your country ... and some not.

Think to verify it before buying ...

Alain

[Fredrick]

Ok, my remote controll to my car is 433MHz so i asume that that is what i should buy.

[mackrackit]

The frequency is the only difference.

Here is a thread with some sample code
http://www.picbasic.co.uk/forum/show...0584#post50584

[dhouston]

The frequency and the allowed output power differ depending on the region or country. Europe uses 433.92MHz and allows far more power than is allowed in N. America.

[Fredrick]

Have just placed an order for 2 433.9 MHz transmitters and 2 recivers..

The parallax manual says upp to 500+ feets and LINX says upp to 3000 Feets, what is the actul range?
Can i make parallax 433.9 MHz transmitter to send whit more power?

[Fredrick]

Have looked at the datasheet for the TXM-433-LR and find an intressting point.

USING LADJ
The Level Adjust (LADJ) line allows the transmitter’s output power to be easily
adjusted for range control, lower power consumption, or to meet legal
requirements. This is done by placing a resistor between VCC and LADJ. The
value of the resistor determines the output power level. When LADJ is connected
to VCC, the output power and current consumption will be at its maximum. Figure
4 on Page 3 shows a graph of the output power vs. LADJ resistance.
This line is very useful during FCC testing to compensate for antenna gain or
other product-specific issues that may cause the output power to exceed legal
limits. A variable resistor can be temporarily used so that the test lab can
precisely adjust the output power to the maximum level allowed by law. The
variable resistor’s value can be noted and a fixed resistor substituted for final
testing. Even in designs where attenuation is not anticipated, it is a good idea to
place a resistor pad connected to LADJ and VCC so that it can be used if needed.
For more sophisticated designs, LADJ can be also controlled by a DAC or digital
potentiometer to allow precise and digitally variable output power control.

It´s look like i can easy modifie my RF module to work whit the range of 3000 feet or (900 meters) by removing or replace the resitor R5 (se Picture), and i think it´s still legal i sweden to transmit at this ranges on the private 433.92 MHz band.

http://www.parallax.com/Portals/0/Im...79/27980-L.jpg

[mackrackit]

As others have said check your local laws.

You are reading the data sheet, did you see the part about 3 volts. Do not make the mistake of using 5 volts like you normally would with a PIC.

[Fredrick]

As others have said check your local laws.

You are reading the data sheet, did you see the part about 3 volts. Do not make the mistake of using 5 volts like you normally would with a PIC.

The Typical voltage for the LINX module is 3 volts and the parallax module need 5 volts so i assume that there is an voltage regulator on board.

So if i measure the voltage between GND and infront of the resistor R5 and have 3 volts it shold not be an problem to just bypass the restistor to get maximun power or?

I just check the local law and there is no problem to run at maximun power on the 433.92 MHz band.

[dhouston]

The legal limits are on the radiated power not distance. Distance is heavily influenced by environment. It's impossible to say whether you are within the legal limits without some sophisticated and expensive test equipment. The tests required by the FCC for the USA cost about $US3000.

You can see the limits here...

• http://www.radiometrix.co.uk/apps/apnt102.htm

Of course, whether the authorities will catch you and punish you if you exceed the limits is another matter.

[Fredrick]

The legal limits are on the radiated power not distance. Distance is heavily influenced by environment. It's impossible to say whether you are within the legal limits without some sophisticated and expensive test equipment. The tests required by the FCC for the USA cost about $US3000.

You can see the limits here...

• http://www.radiometrix.co.uk/apps/apnt102.htm

Of course, whether the authorities will catch you and punish you if you exceed the limits is another matter.

Ok... but in teori (legel or not) i only have to bypass or change the resistor R5 to another value.... or?

In the doc i find the limit is Max 25 mW in sweden not 10mW.
http://www.scanner.nu/pdf/riks.pdf (it´s i swedish)

[mackrackit]

Ok... but in teori (legel or not) i only have to bypass or change the resistor R5 to another value.... or?

In the doc i find the limit is Max 25 mW in sweden not 10mW.
http://www.scanner.nu/pdf/riks.pdf (it´s i swedish)

If R5 is connected to LADJ then you may be right. Just remember the max voltage of 3 any place on the LINX.

Another way to get maximum distance from any radio is to use a good antenna. I doubt the , as we call them here "duckie" that is on the Parallax is very good. Most duckies are not very good for for distance.

A quarter wave with ground plane or a half wave will work the best for distance at any power.

I think dhouston has antenna info on his web site. Or google for a ham radio site for more info. The antenna is half of the radio in terms of performance.

[dhouston]

I've never used the Parallax receiver and transmitter so there may be reasons why the things I've learned with the simpler (and order of magnitude cheaper) TWS transmitters and receivers may not all be applicable.

From the LADJ excerpt that was quoted, shorting the resistor so that Vcc is applied to LADJ will give maximum output power from the transmitter.

The distance above the ground will also have a big effect on range. Reflections/refractions from the ground, buildings, trees, etc. degrade the signal. Most of the range estimates that accompany these devices are outdoor, line-of-sight figures. Indoors, my rule of thumb estimate is 20-25% of the outdoor figure.

An efficient, directional antenna (e.g. a yagi) on both the transmitter and receiver can give you large increases in range by concentrating the power in one direction rather than spreading it equally in all directions. The stubby antennas on the Parallax modules are not very efficient and are omni-directional. There are some yagi antennas for this frequency that are printed on circuit boards (or even mylar). Here's an example...

• http://www.wa5vjb.com/products1.html

A wideband preamp between antenna and receiver can also give a big increase in range but this may not work with all receiver designs. In some cases, the increased signal can overwhelm a receiver but I've used them successfully with the TWS receivers and have even tested with 2-3 of them cascaded. This has one major advantage - it does not violate any of the legal limits on transmitted power levels.

[Fredrick]

Ok thanx for the information.

I agree that Parallax is expensive but i need the LINX module on an PCB becouse i don´t have the things needed to make my on PCB´s.

[mackrackit]

Ok thanx for the information.

I agree that Parallax is expensive but i need the LINX module on an PCB becouse i don´t have the things needed to make my on PCB´s.

http://www.rentron.com/remote_control/TXLC-XXX-LR.htm

[Fredrick]

Yes i have lookt at Rentron but 2 transmitter and 2 recivers + 2 anntena coast $111 and at parallax $109,95 with antenna.

[mackrackit]

Yes i have lookt at Rentron but 2 transmitter and 2 recivers + 2 anntena coast $111 and at parallax $109,95 with antenna.

OK, but the antennas from parallax do not look very good (very short ), the ones from rentron are 1/4 wave.

As I said before, the antenna will make all the difference for long range.

Let us know how it goes.

[Fredrick]

Yes i will inform how it goes, and maybe i will come with some questions on the PBP program for the recivers and transmitter.

[Fredrick]

Are the Linx RF modules FM och AM?
Can´t find anything in the datasheet?

[mackrackit]

Neither, More like CM.
From the data sheet

When a logic ‘1’ is present on the DATA line and the PDN line is high, then the
Power Amplifier (PA) will be activated and the carrier frequency will be sent to
the antenna port. When a logic ‘0’ is present on the DATA line or the PDN line is
low, the PA is deactivated and the carrier is fully suppressed.

So, the only thing they can transmit is bits, think of Morse Code. ON OFF
That is why they work so well for serial communications.
Also, that is the reason for sending a "train" signal (010101010101) allows the receiver to balance the internal capacitor before receiving the real data.

I think the correct way of saying it is Carrier Present - Carrier Absent

[dhouston]

I think the correct way of saying it is Carrier Present - Carrier Absent

Or OOK (On-Off Keying), ASK (Amplitude Shift Keying) or AM (Amplitude Modulation). And FSK (Frequency Shift Keying) works much better but costs much more.

[Fredrick]

Thank you.

Now i have recived the Parallax RF modules and write this test programs

Transmitter PIC16F628A whit Internal RC OSC at 4 MHz

<html>
<head></head>
<body><!--StartFragment--><pre><code><font color="#008000"><i>
</i></font>CMCON = <font color="#808080">7 </font><font color="#008000"><i>'Alla I/O Digitala
</i></font>LEDPin <font color="#000080">VAR </font>PORTB.<font color="#808080">0
</font>TransmitterPIN <font color="#000080">VAR </font>PORTB.<font color="#808080">4
</font><font color="#000080">INCLUDE </font><font color="#FF0000">&quot;modedefs.bas&quot;
</font>Counter <font color="#000080">VAR BYTE
</font>Synk <font color="#000080">VAR BYTE
</font>Synk = <font color="#808080">$55
</font><font color="#000080">DEFINE </font>CHAR_PACING <font color="#808080">1000
</font>Counter = <font color="#808080">0

</font>Main:
    <font color="#000080">HIGH </font>LEDPin
    <font color="#000080">PAUSE </font><font color="#808080">100
    </font><font color="#000080">LOW </font>LEDPin
    <font color="#000080">PAUSE </font><font color="#808080">100
    
    </font><font color="#000080">SEROUT </font>TransmitterPIN,T1200,[Synk,Synk,Synk,Synk,Synk,Synk,<font color="#808080">9</font>,Counter]

    <font color="#000080">HIGH </font>LEDPin
    <font color="#000080">PAUSE </font><font color="#808080">100
    </font><font color="#000080">LOW </font>LEDPin
    <font color="#000080">PAUSE </font><font color="#808080">100
    
    </font>Counter = Counter + <font color="#808080">1
    </font><font color="#000080">PAUSE </font><font color="#808080">600
</font><font color="#000080">GOTO </font>Main
<font color="#000080">END 


</font></code></pre><!--EndFragment--></body>
</html>

Reciver PIC16F872 with 20 MHz OSC

<html>
<head></head>
<body><!--StartFragment--><pre><code><font color="#008000"><i>
</i></font><font color="#000080">DEFINE </font>OSC <font color="#808080">20
</font><font color="#000080">DEFINE </font>LCD_COMMANDUS <font color="#808080">3000   </font><font color="#008000"><i>'Set command delay time in us
</i></font><font color="#000080">DEFINE </font>LCD_DATAUS <font color="#808080">200       </font><font color="#008000"><i>'Set data delay time in us

</i></font><font color="#000080">INCLUDE </font><font color="#FF0000">&quot;modedefs.bas&quot;
</font>Counter <font color="#000080">VAR WORD
</font>ReciverPIN <font color="#000080">VAR </font>PORTC.<font color="#808080">0
</font>ADCON1 = <font color="#808080">7 </font><font color="#008000"><i>' Alla digitala
</i></font><font color="#000080">PAUSE </font><font color="#808080">500

</font>Main:
    <font color="#000080">SERIN </font>ReciverPIN,T1200,[<font color="#808080">9</font>],Counter
    <font color="#000080">GOSUB </font>LCD
<font color="#000080">GOTO </font>Main

LCD:
    <font color="#000080">LCDOUT </font><font color="#808080">$FE</font>,<font color="#808080">1  
    </font><font color="#000080">LCDOUT </font><font color="#808080">$FE</font>,<font color="#808080">$80</font>,#Counter
    <font color="#000080">PAUSE </font><font color="#808080">500        
</font><font color="#000080">RETURN

END 
</font></code></pre><!--EndFragment--></body>
</html>

It´s working very well whit in the rance of 50 - 60 meters whit the transmitter indoors and the reciver outdoors, but when i take the reciver also indoors in a house 50 - 60 meters away from the transmitter the counter on the reciver display starts to show wrong numbers sometimes but it´s still counting... but whit the reciver outdoors it does not miss a single number whit in 50 - 60 meters.

Any idé how i can to improve my code?

I´going to do some more tests to tomorrow, it´s soon time to sleep here in sweden...

[skimask]

Any idé how i can to improve my code?

RF is tricky, no matter what you do. Just too many variables for the average joe to account for, circuit layout, power stability, sunspot cycle, and so on and so on...

My experiences: (which are far outweighted by a number of people on these forums when it comes to RF)
-Try changing the number of sync bytes in the transmitter...6 sync's is a good start. Try 2, try 10, try anything, see what happens.
-Try changing the baud rate. I had a TX434 from Rentron. The datasheets say it's only good for 4800bps. I got it to work very reliably at 9,600 and fairly decent up to 19,200, but it didn't like 2400bps. Try 2400, try 9600, try 4800...
-Change the PACING length. You have it set at 1000, a decent number. But...maybe the RF module wants less. If you have 1ms between each character, that also means that you have 1ms between each sync character, which may be screwing up your sync'ing, which may mean that the data slicer isn't being balanced completely. Try leaving out the PACING altogether, sending your sync bytes as fast as possible, then manually PACING your sent bytes with a slight pause in between each character.

[dhouston]

Any idé how i can to improve my code?

Get a better antenna at the receiver. You can build a very simple but very good one from plans on my web page.

• http://davehouston.org/eggbeater.htm

Any solid copper insulated wire will work (the bigger the wire diameter, the better) or you can even use copper tubing if you can insulate it, and you can cheat by using 75-ohm coax for the phasing line. If you still need more range, then add a wideband preamp between the receiving antenna and receiver - it's the Ten-Tec 1001.

• http://www.aoruk.com/tentec/kits/1001/1001.htm

Ignore the picture - it's the wrong one.

And try without pacing.

[Fredrick]

When i disconnect the power from the transmitter the reciver display still shows numbers, but does not count from 0 to 255, it´s shows 1, 244, 34, 55, 23, 99, 138, 232, 233 and so on.... where does this numbers come from?

[mackrackit]

Sounds like random noise. There is RF every where.

I think the internal "slicing" capacitor is wondering around giving false data.

If this is the case, depending on what you are going to use this for the solution can pretty easy.

If you are sending commands for a remote control the easy way is to have something like

SERIN ReciverPIN,T1200,[9],Counter
IF Counter = ??? THEN 
XYZ 
ELSE
QRS

If you are sending data like what you are now, you may need to set up a way to verify the data. Some sort of encoding / checksums...

The Linx web site has some info on this and dhoustion has a protocal on his web site.

[Bruce]

I'm not familiar with the Parallax modules, but if they use the Linx LR series, then this receiver will output random noise even if the transmitter is powered down.

Look at the examples on dhoustons' website, and others he has posted here. He knows what he's doing.

You might also try a search here. I have posted several code examples for RF communications that are very simple to implement, and work quite well with PBP & noisy receivers.

It's just not that simple to get a reliable wireless connection up & going, and it's for sure not going to be anywhere near as simple as a 'wired connection', but there are enough threads here 'with code examples' that cover this if you look hard enough.

[dhouston]

Like Bruce, I'm unfamiliar with the modules you chose. From your description it seems like they are superregenerative receivers. See

• http://davehouston.org/rf-noise.htm

for an explanation of the noisy output. It can be caused by environmental factors or come from internal noise sources (e.g. resistors).

Using SerIn with this type of receiver creates two problems. One is that SerIn samples the data at the mid-point of the bit period. If the output is high at that time, you get a 1 bit and, if low, you get a 0 bit. Random noise can give you either state. The other problem is that you need to set the receiver AGC and ATC (Automatic Gain Control & Automatic Threshold Control) and you need to signal the receiver that some data is on the way. The sync bytes recommended by several people who post here are intended to serve those purposes. EDIT: If you look at the bottom picture at the above referenced link, you can see how a signal very much like the sync bytes only gradually emerges from the noise. There is a better way but it depends on the type of data that you wish to transmit.

I would only use SerOut/SerIn if I wanted to send text or lengthy data packets. And these receivers are not the best choice for either. FSK gets away from noise and the receiver has a CD (Carrier Detect) output that tells you when data is coming. FSK modules cost more than ASK but not as much as the ones you've chosen.

For short data packets, I prefer ASK and the NEC protocol illustrated in this thread

• http://www.picbasic.co.uk/forum/showthread.php?t=6261

The long lead-in pulse sets AGC & ATC and signals that a data packet follows. Since the output is only monitored after seeing the long lead-in, random noise is much less of an issue. Instead of sampling at mid-bit, the receive routine measures the length of the spaces between pulses so it's less likely to be fooled by noise or its absence at mid-bit. (It's even better to measure between rising edges but that requires interrupts.) And each byte is sent twice in bitwise complementary form so error detection is built-in.

What is the nature of the data that you want to transmit?

[Fredrick]

What is the nature of the data that you want to transmit?

I just buy them to play and try to learn something so i don´t have any nature of data to transmit.

[mackrackit]

I just buy them to play and try to learn something so i don´t have any nature of data to transmit.

COOL! Whats next?

[Fredrick]

COOL! Whats next?

I don´t know but now i will try to get this to work better.

[Luciano]

Hi,

From page 3:
http://www.parallax.com/Portals/0/Do...ceive-v1.0.pdf


Calibration
When initiating communication between the RF modules, a sync pulse should be sent
to re-establish the radio connection between the modules. Sending several characters
can accomplish this, however sending a pulse (which maintains a high state during the
synchronization) is more efficient.

See page 6 for the BS2 code samples.


* * *

RSSI PIN (Received Signal Strength Indicator)

This line will supply an analog voltage that is proportional
to the strength of the received signal.


Can you test that and post the results?

(Do not connect the PIC microcontrollers during this test).


Step 1: Connect a digital voltmeter to the RSSI PIN of the receiver.
(Make sure the multimeter is set to DC volt and that you measure from the RSSI PIN to GND).
Power on the receiver and make sure the transmitter is powered off.
Q1: What voltage do you get on the RSSI PIN of the receiver?


Step 2: Power on the transmitter.
Q2: What voltage do you get on the RSSI PIN of the receiver?
(The transmitter and the Receiver are powered on).

Step 3: Connect +5V via a 1k ohm series resistor to the DATA pin of the transmitter.
(The transmitter and the receiver are powered on).
Q3: What voltage do you get on the RSSI PIN of the receiver?

Step 4: Connect GND via a 1k ohm series resistor to the DATA pin of the transmitter.
(The transmitter and the receiver are powered on).
Q4: What voltage do you get on the RSSI PIN of the receiver?

Best regards,

Luciano

* * *
EDIT:

These are the RF modules used by Parallax:

LR Series RF Transmitter Module Data Guide
http://www.linxtechnologies.com/Docu...Data_Guide.pdf

LR Series RF Receiver Module Data Guide
http://www.linxtechnologies.com/Docu...Data_Guide.pdf

[dhouston]

I just buy them to play and try to learn something so i don´t have any nature of data to transmit.

I looked briefly at the datasheet and these do use the Lynx RXM-433-LR-S chip which is a superhet design (the same one Bruce sells). This has a little better sensitivity and a little less noise than a superregenerative receiver like the RWS-434 but, in essence, it's an AM radio receiver and the noise you see in the absence of a signal is equivalent to the noise you hear on an AM radio when it's tuned between stations.

You can make use of the RSSI pin. Connect it to one of the PIC's ADC pins to get a measure of signal strength. You can use this to compare different antennas, etc.

You can also see the output signal using the techniques I've described here.

• http://davehouston.org/learn.htm

[Fredrick]

Calibration
When initiating communication between the RF modules, a sync pulse should be sent
to re-establish the radio connection between the modules. Sending several characters
can accomplish this, however sending a pulse (which maintains a high state during the
synchronization) is more efficient.

How to i know how the the period of the puls?

There is diffrent periods for BS1 and BS2 and mybe another period for my PIC?