Proper connections using Parallax's 433MHz Transceivers

eiplanner

Hello all,

I am still working with the Parallax 433 MHz transceivers to communicate between my BS2 and Prop PDB.

Because I have let the smoke out of one of my modules, I want to clarify a few things before attempting to
hook up my new one.

Below are the wiring diagrams that Beau in another thread. I wanna make sure that I am correctly applying
this configuration. Please correct me where I might be wrong.

On my Propeller:

* Should I have 3 dedicated pins (1 for data, 1 for transmit and 1 for receive) with the transmit pin going through
a 330 ohm resistor? (Both the trans pin and the rec pin terminating on the TX-RX of the module)

On my BS2:

* Should I be using voltage dividers on all lines to the module (5v input, trans/recv, and data pins) or will the module
regulate its own voltage? Beau listed the RF transmitter and RF receiver modules but I am using the Transceiver
module on my BS2 Homework Board and need to get correct connecting arrangement of resistors.

Thanks for your expertise on this.

Raymond

 

Beau's Diagrams:

Use this schematic when using the RF transmitter (#27980)

               4.7K         1K
+3.3V >---/\/\---o---/\/\---> DATA
                 |
   TX >----------o
    Vss >---------------------> GND
   +5V >---------------------> +5V



Use this schematic when using the RF receiver (#27981)

             4.7K         1K
GND >---/\/\---o---/\/\---> DATA
               |
 RX >----------o
  Vss >---------------------> GND
 +5V >---------------------> +5V



Use this schematic when using the RF transceiver (#27982) as a Transmitter

                330
     TX >---/\/\---------> DATA

    Vss >----------------> GND

+3.3V >----------------> TX-RX



Use this schematic when using the RF transceiver (#27982) as a Receiver


RX  >------------------> DATA

Vss >------------------> GND

Vss >------------------> TX-RX

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and so, the journey continues..........

evil_pic

Raymond

I'm trying to do something similar and think that I've got some issues with my 27982 transcievers. when you look at the LINX technologies datasheet for the TRM-XXX-LT module the max voltage is 3.6V. however when you look at the Parallax datasheet it says 3.3 - 5.0V. I've checked the pins on the actual chip and if you put 5V on the Vdd pin of the 27982 you dod get about 3.3V on the Vcc pin of the LINx module.

one problem I've had is getting the data through one module over the air and out the data pin on the other module. A lot of the time I'm getting partial data out. I'm not sure if I'm using the right configuration on my serial command. i'm using the drive mode, but I've seen reference to open mode. What are you using? i'm also using the same pin for both transmit and receive. Do you pull the receive pin high or low?

Thanks,
Dave

eiplanner

@evil

These Parallax Transceivers (27982) are quite the problem child to put it lightly. I have been working with mine every day for two weeks or more and have yet
to get a consistent result. When I set the TX-RX pin to low for receiving data, it automatically starts receiving trash out of the air. This makes it extremely difficult
to ever get the modules synchronized.

I have used all kinds of programming configurations to no avail. Changing baud rates, using preambles, serin, pulsein, pin mode, i've pulled them high, pulled them low, voltage dividers,
filter caps, and all kinds of other unorthodox methods, and still no usable results. There always seams to be an incoming stray bit that throws everything off.

It's the same on my Pro Dev Board in Spin. I can't get it to sit at a waitpeq command for more than half a second. The modules are just picking up too much trash.
It won't even hold at a serin command that has to wait for a signal before receiving data. It just picks up some arbitrary high bit and starts receiving all on it's own.

I am not a veteran programmer, but I have been at this serial stuff for a couple months and I believe that I pretty well have the gist of what needs to be done and several
ways to accomplish it, but I don't know if it will happen with these modules. I have been considering removal of the LINX chip from the board to be used as illustrated on its
datasheet. That way maybe I could take more control of it and possibly filter it better.

Currently, I am working on a totally non-synchronized method of sending long pulses of 1's and 0's from my Prop Transceiver to my BS2 transceiver. I am having some luck
with generating good signals by making my stamp check the length of the pulse with a looping BUTTON command. It continuously runs the loop until it gets a complete signal
such as %111111111111111 then leaves the loop to assign a bit value to a byte variable. Then back to the loop to get the next piece of data. It's a little slower but right now,
it's the only way I can get the data across .

Sorry not much help. I've searched the forums many times myself and haven't come across and real solutions for these modules between the Pro & Stamp. I haven't
tried coms between two Props yet. I was wanting to use the buttons on my PDB to remote control my Boe-Bot just for fun and practice with the two different boards
and languages.

I'm still determined though so maybe, I'll have a usable object sooner or later.

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and so, the journey continues..........

Mike Green

@eiplanner - The Parallax transceivers are very simple devices. You're obviously in a noisy area which happens sometimes. The only solution to noise as you describe is to change frequency or add error detection and correction. There's sample code on the product page for the transceivers that generates a CRC for data to be sent, checks it on receive, and allows a program to discard it (or request a retransmission). If you want more reliable transmission, you should try something like the xBee. These modules have their own microcontroller built-in and do their own checking and retries so that what the Stamp or Propeller sees is the checked and corrected data.

You can keep playing around, but you really need to look into well established techniques for reliable digital transmission over a noisy communications link. This sort of thing is used all the time in amateur radio and the CRC examples for the Stamp are a good starting point.

There's nothing wrong with the Parallax transceivers and they work well for a lot of people. Unfortunately, the same frequencies are used for a lot of devices and, in noisy areas, you have to add your own error recovery layers.

ToeTag

Hi eiplanner, im doing exactly the same thing as you are doing and im having a bit of the same problems, im using two STK-500 with an ATMega16 in each, ive hooked up one computer to each of them and done the basic rs232-serial test with sending and mirroring what was sent back to the hyperterminal (with both of them separately using standard UART routines), I've also sent data inbetween the computers by connecting the RS232-spare's TX->RX and RX->TX with the result that i can type data on one of the computers and it shows on the hyperterminal on the other... so far so well, now im trying to do the same with Parallax Transceivers #27982, on the Transmit-side ive set the TX-RX, and PDN high, on the recieve-side the PDN high and TX-RX low so that it acts as a reciever (ofc the VCC and GND are coupled as they should be). With that setup nothing happens when im sending data inbetween the computers, but if I pull out the cable to PDN (power down mode) on the receiving side it displays A LOT of Smile, i understand this is rubbish form disturbances, but i can see an increase in print-speed if I send data from the transmit-side at the same time.

My conclusion is that what im sending is drowning in this rubbish data, but why wont anything registered when im in PDN high mode? ive tried all the different tecniques of manchester coding, sync-bytes etc etc without any success so far. I've got some tricks up my sleeve left to try. If im not successful this weekend I'll grab my mechatronics teacher/assistants at school on monday to get some advice... If you've solved this already (since it was a couple of days since you posted) I'd be glad to hear from you!

w8an

I agree with Mike about the XBee idea. I just got a few of these yesterday and hooked a couple of them up today to test. Out of the box, they will talk to each other at 9600 baud with NO CONFIGURATION. Of course you can do a lot of configuration to set up private LANs, assemble packets, adjust data speeds, etc. Also, the price is comparable to the 433 MHz transceivers.

I had them talking in just a couple minutes after hooking up the hardware. It truly was a no-brainer!

--Steve

Leon

Those simple 433 MHz transceivers probably need Manchester code to work properly.

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Leon Heller
Amateur radio callsign: G1HSM

ToeTag

@w8an

haha, lucky you! though struggeling to get this to work is a good way to learn it all, since this is a part of my engineering education I MUST know how this works in every little detail, and its a nice feeling when you get it up and running if you've been working for it some time^^


EDIT!

@eiplanner

I've got the RF-connection up and running today! I measured the Tx-Rx pin on the transmit side just to discover it wasnt logic 1, So i checked my code again and nothing was wrong, but just to be on the safe side i removed my DDRB and PORTB assignments (i set PORTB to 0xFF, s

w8an

If you've got the time, then great. I prefer to focus my efforts on the big picture, however, and the XBee API mode is exactly what I need for my app.

Glad you got yours working!

ToeTag

ah I see, what do intend to you use them for? My plan is to remote control a lamp that im using for wild boar-hunting ^^ but probably not with parallax transceivers since they cost $40, im just using them for my 3'd-year project in school

w8an

Portable units in a manufacturing plant to post various sensor data to a central database. The real spiffy part of the XBee is that I don't even need a microprocessor at the sensor end since the device has analog and digital inputs. They can be programmed to periodically transmit the values of those inputs.

ToeTag

ok, yeah if you just want to get data from point A to B as effortless as possible i guess xbee is a way better choice than pure RF ^^ , I can't really see why RF is so much more expensive than Xbee? Xbee should be the obvious choice for anyone who wants to implement a wireless solution to just about anything...though by looking at the manuals of a xbee and compare it to a RF -transceiver i notice that the current consumed is about 1/4 to 1/5 of a Xbee, RF might be a better choice if its batterypowered...

Post Edited (ToeTag) : 3/1/2010 1:01:31 AM GMT

RickInTexas

I used a LINX setup for a remote controlled lap counter setup at our local velodrome. I researched and found that 433 Mhz is indeed a noisy band. I got a 418Mhz set, but unfortunately they DC'd all devices on that freq.

These work ​flawlessly with very good range, about 2 city blocks, line of site.