SparkFun Forums

[chips]

I apologize in advance if my questions appear trivial for this forum. As a novice, I am eager for advice, website recommendations, or book recommendations regarding my questions.

I recently purchased the RF Link - 2400bps with the intention of sending temperature and pressure sensor data wirelessly. In a wired circuit, I am familiar with parallel data transmission; however, I am unsure how to send this same data wirelessly through serial transmission.

How do I convert my parallel data to serial?
How do I transmit this serial data using the RF Link - 2400bps (i.e. what is a common protocol)?
Is an UART controller required for the RF Link - 2400bps?

Thanks,

-David

[b_bogk77]

I'm far from being an expert, but you will probably have to send the data 1 bit at a time.

For each bit, hold the tx line low or high a certain amount of time.
At that bit rate you can probably implement the sender in software.

Also, you will probably need to add some bits for error correction.

[saipan59]

Browse this forum for topics related to this.
To make something that really works, it's quite a bit more complicated than what the previous reply by b_bogk77 would indicate.

Several of us (at least) have it working.
In general, you will need a uC on each end of the link, and a software protocol to move the data.

Pete

[satz]

Hi,

Take a look at this thread. It contains information and links that you should find useful

S

[satz]

Hi,

Sorry, forgot to post the link:

viewtopic.php?t=5369


S

[manuka]

A great deal of 433.92MHz data work has been easily done using PICAXE micros. See => www.picaxe.orcon.net.nz

[riden]

A great deal of 433.92MHz data work has been easily done using PICAXE micros. See => www.picaxe.orcon.net.nz

I would have to agree, that the PICAXE makes things easy. Too easy. Just kidding.

David, it is likely that your temperature and pressure devices are easily supported by the PICAXE and that will make the data transfer easier. As Pete has said, you do need a protocol because of the nature of the TX/RX link. This has been discussed on the forum and you could use some of the BASIC examples almost verbatim with the PICAXE.

As many times as the topic of RF links comes up, maybe a few of us should create a tutorial to help others (each of us providing examples in the language of their choice). I'd be happy to contribute Proton/PIC BASIC and PICAXE code as well as other text, as needed.

[chips]

First of all, thanks to all who posted replies to this thread.

Plowing through, I figured out some answers to my own questions. The following may be useful to beginners like me:

How do I convert my parallel data to serial?

You can use a parallel-in serial-out shift register (DM74ALS165 from Fairchild).

How do I transmit this serial data using the RF Link - 2400bps (i.e. what is a common protocol)?

Since I was just interested in having my 8-bits show up on my receiver, I found an encoder/decoder pair (CIP-8E/CIP-8D from Reynolds Electronics). The encoder/decoder pair took care of my parallel to serial to parallel conversions. All I had to do was connect the digital out of the encoder to the DATA pin of the transmitter and connect the DATA pin of the Receiver to the digital in pin of the decoder.


-David

[stevech]

The most common way serial/parallel data is handled for low speed wireless in cost-sensitive designs with microprocessors is for your firmware to do the correct timing and bit coding to send and decode. That is, you are doing serialization in your application code.

But, if you don't mind another chip, what you speak of is fine. Beware the choice of bit coding versus the kind of transmission modulation you're using for the selected transmitter/receiver, i.e., OOK versus FM.

When your costs approach $19 per device for wireless, you can consider a plug-and-play module such as one of the many suppliers of IEEE 802.15.4 modules. Such as Maxstream XBee. If that's your preference... just connect it's serial port to your microprocessor's serial port. But, maybe you want to learn the lowest levels of wireless protocols and error detection and correction and modulation coding.