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I need a pointer in the right direction -Radio RX/TX
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I need a pointer in the right direction -Radio RX/TX

by tytower on Tue Oct 06, 2009 1:07 am

I have a set of devices similar to this
http://www.sparkfun.com/commerce/produc ... ts_id=8950

I will drive the transmitter from an arduino programmed to do so.

On the receiving side I wondered if I could use a USB to DB9 com port device to receive the data put out directly connecting the data line direct to the RX line and ground to ground onthe DB9 pins . I should then be able to power up the receiver device from 5 V I steal from the USB port device .

My thought is that the receiver will output immediately whatever input it receives as a radio transmission straight into the DB9 serial port to a hyperterminal type input.

Will this work can it be done this way . Is there another way without another Arduino board?

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Re: I need a pointer in the right direction -Radio RX/TX

by Trajetre on Tue Oct 06, 2009 3:06 am

From what I understand and read here, the whole thing is as easy as powering the modules, and sending TX from the Arduino on the transmitter to receive the same bytes (at 4800bps or below, remember!) on the RX of the 5V transmitter, which could be read by an appropriate USB to 5V level logic serial converter (but not a standard DB9 +/-12V serial port).

I can't guarantee that your particular USB->DB9 serial adapter will work with a direct hookup to the DB9 connector though, as many of them use level converting charge pump chips (similar to the MAX232) to boost output voltage to 7 to 12V, and expect similar voltages (sometimes negative for zeros) for communication. I tried with my own Arduino to a 0 to 10V output adapter (this diagram was useful) and it failed (signals seen, but gibberish, works if tapping directly into the 5V USB converter chip upstream from the level converter). You'll probably see the same if you try to communicate with 5V serial from an Arduino through a DB9 RS-232-level USB to serial converter.

Either use a 5V-level USB to serial adapter, or make one out of your current adapter by tapping into the TX and RX lines on the tiny USB converter chip with mad soldering skills. Regardless, you probably won't regret getting the new communication tool.

Also, if you happen to have an adapter similar to this one with a PL2303 chip, I can probably guide you through the mad soldering process.
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Re: I need a pointer in the right direction -Radio RX/TX

by tytower on Tue Oct 06, 2009 4:32 am

Most helpful .Thanks

I do have the PL2303 chip in mine and my receiver module is a 5V @10mA so I will study your post closely. Perhaps you have a site covering this mad soldering and what does the mad mean?.

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Re: I need a pointer in the right direction -Radio RX/TX

by Trajetre on Tue Oct 06, 2009 2:49 pm

Currently I don't have a writeup of tapping the TX and RX lines in that USB to serial converter, and I can't seem to find anything simple in searches of Google or Instructables, and perhaps worst of all, my camera's battery just died. Just as I was writing this post. Which means I'm significantly less helpful.

"Mad ____ skills" is just slang meaning "ridiculously good ____ skills," perhaps on the level of a savant. I meant that because the chip has very closely spaced pins (the same package as this guy), it is very difficult to solder to individual pins without bridging two of them.

Unfortunately, according to the PL2303 spec sheet, page 11, the RXD pin (which you would use to receive the signal from the radio reciever) is pin 5, which is nested right in there amongst the other pins. I typically manage to solder directly to the pin on my own hacked USB to Serial converters by presoldering very small wire and using a fine soldering pencil tip, but it requires some skill and experience. If you can, try to find a convenient via, exposed trace, or less densely packed smd component that it connects to, and solder in there. Or just buy the cable.

I'll try to get better instructions up when I can get my camera battery recharged (no small task, since I lost the charger!).
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Re: I need a pointer in the right direction -Radio RX/TX

by richms on Sat Oct 10, 2009 4:16 am

Those bare RF transmitters get loads of noise in them.

I had a play with some 433MHz ones, and everytime someone was to hit their garage opener I would get to see loads of noise. There was noise most of the time when not transmitting at the other end, so there had to be a few chars that were junk before the actual data transmitted so that it would sort itself out into the serial port. For ages it was dying sometimes - turns out that I needed to have timeouts in my protocol since it would often get noise that was valid.

They are no xbee when it comes to being easy or reliable.

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Re: I need a pointer in the right direction -Radio RX/TX

by tytower on Sat Oct 10, 2009 8:27 am

richms wrote:Those bare RF transmitters get loads of noise in them.
They are no xbee when it comes to being easy or reliable.


Logically speaking whats the difference? They both deal with data transmission over the air. I would expect they both had PLL,Phase Locked Loops, Do the XBees use ASK transmissions ? Noise is on all receivers ,listen to a thunderstorm one night. The trick is to get the message through despite the noise

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Re: I need a pointer in the right direction -Radio RX/TX

by Fjornir on Sat Oct 10, 2009 4:06 pm

tytower wrote:Logically speaking whats the difference?


I'm not super familiar with the xbee modules but I'll try to give you an answer. With the modules like the sparkfun module you linked you're sending (and receiving) raw serial over the airwaves. The burden is on you to handle checksums, resend-on-error, collisions if you have more than one transmitter in the area, and the like. With an xbee module a lot of that is handled for you; you send a packet and can, largely, ignore the transport details - I think the xbee module with a packet to send will wait until the freq is open, send your data and a sum, wait for an ack (or a resend request) and if needed retransmit, I think they have some rudimentary routing in place, and a number of other features to take care of the grunt-work of wireless mesh networks for you.
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Re: I need a pointer in the right direction -Radio RX/TX

by tytower on Sun Oct 11, 2009 8:51 am

I've gone to VirtualWire in the Arduino library. It refused to compile at first but a bit of searching got that fixed .I've built the transmitter and it seems to be doing what it should. The programming examples are a real boon

I'm waiting on another arduino board to arrive before I can program it for receive . I decided If I was going to pay $20 US for a FTDI cable I might as well use a $35 US Arduino board programmed to receive and then use it later for something else when the system is up and running.

I'll pass on the results of this to see that the radio TX/RX all works as it should

My radio modules are from here Oatley Electronics
http://secure.oatleyelectronics.com//product_info.php?cPath=47&products_id=384&osCsid=27747b908076005543b9fb9c087b37ca

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