Wireless with DS18S20

[Jerson]

Lerameur

I suspect you too are using one of the ASK modulated RF modules. I understand from your code that you are Manchester coding the data to send to keep the module happy. However, I find the modules work best when you have just 4-5 bytes to send. Keep the messages short. So, I have used the following technique to send data properly. Of course, it helps to mention that RF shielding is very important for the receiver module in case you have the OEM version.

          // wait for a packet marker RJ
          serin2  RxD,  Baud, [WAIT("RJ"), HEX1 Acc1]

          // now disable the receiver since we got the data we need
          RxDisable = 1

          // if the data is for me, process it
          if (ID = Acc1) then
            pause 100               ' this delay is to allow the RX01 to turn off
                                         ' to prevent RF collision with multiple devices
            Pot PotPort, 255, Acc1  ' read pot position and send

            // Send the reply with ACC1 having the value to send
            // the lower case rj is the packet marker to indicate acknowledge
            Serout2 Txd,Baud,[$55,$55,$55,"rj", HEX1 ID,",",Dec2 Acc1]
          endif

As you see, I haven't used any encoding and do happen to send the data properly. The trick here is that keeping the message short tricks the receiver into reading the data properly before the signal strength droops at the receiver end.

You may add LRC (Checksum) which will help you choose the good data packets and throw away the corrupted ones.

Jerson

[lerameur]

I use this module here:
http://www.robotshop.ca/home/product...ity-tx-rx.html
is it OOK module ??

I finished building the sending module with the LCD wirelessly. The module ALWAYS indicate a good temperature. So it has to do with the RF part.

k

[Jerson]

Yes it is clearly mentioned in the datasheet to have Amplitude Shift keying modulation. There is a similar thread of recent vintage (about a week old) on this forum that explains how these modules work. Unfortunately, I cant remember the authors name. I shall check and update this post if I find it.

edit : http://www.picbasic.co.uk/forum/showthread.php?t=6212
See post #12

Jerson

[lerameur]

I tried without encoding and I get exactly the same result as with encoding. Slwed end speed up the baud rate had no impact either
ken

[dhouston]

I use this module here:
http://www.robotshop.ca/home/product...ity-tx-rx.html
is it OOK module ??

That's a better receiver than the superregenerative receivers I referred to. And that's a really, really, really good price for a TX/RX pair. Unfortunately, the datasheet really doesn't provide adequate details but I'm guessing it's a superhet or hybrid design and the things I said about AGC & threshold may not apply.

[lerameur]

hi
As for the ground and shielding, should I ground my antrenna or used a metal plate. I have a plastic box, is there a better method ? Of course the second wire of the antenna goes to the input..
ken

[Jerson]

No, no. You have to shield the receiver module as in put it in a metal box with just the antenna sticking out into the open to get the best results.

This is what I did - take a look here http://www.geocities.com/jerson.geo/...6/rfjoy004.jpg

the 2 green wires you see are the antenna for the transmitter and receiver modules

Jerson

[dhouston]

hi
As for the ground and shielding, should I ground my antrenna or used a metal plate. I have a plastic box, is there a better method ? Of course the second wire of the antenna goes to the input..
ken

There's no need for anything special and shielding is usually superfluous unless the receiver is near (6-8') an RF noise source. There are commercial antennas available cut for 433.92MHz or you can build your own - it depends on the range needed. A 6 inch piece of wire attached to pin 8 of the receiver may be adequate. Or you can use one like those sold by Bruce Reynolds...

• http://www.rentron.com/PicBasic/RemoteControl.htm

or build one like...

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

which can be built with any insulated solid wire stiff enough to hold its shape. The phasing line can be made from 75-ohm coax if 93-ohm isn't available.

For the transmitter, a 6" wire is usually more than adequate.

If you need extra range, add a wide-band preamp between the receiving antenna and receiver. Getting 150-200' through a few walls is usually possible.

I've ordered one of the RX/TX pairs so I can test the receiver. In the meantime, can you tell me what the chip is on the receiver? I'm interested in the 24-pin chip - I can tell it's a HiMark chip but cannot read the number. I'm familiar with a HiMark 18-pin superheterodyne ASK receiver chip but cannot recall seeing a 24-pin chip.

[lerameur]

Ok I am getting better reception with grounded antennas.

this is what is written on the 24 pin chip:
0637
BD69F1

ken