A $15.00 FM xmitter...

[hwrdmltn]

This is a FM transmitter that I bought from a company called SPARKFUN - in fact I bought two because I was doing some testing and wanted to be sure I had a backup in case I slipped with a screwdriver. Well, I'm mentioning it here as I see many people needing a good sounding FM transmitter. These sound great. They will not go far - they stay within FCC limits for all the FM broadcast band. They have rock solid frequency stability and can be used on any freq between 88 to 108 Mhz. Freq can be changed on the fly, and they are true stereo (it generates a pilot for stereo) left and right with 75us pre-emphasis and max 2 milliwatt RF output which with a 22-27 inch antenna will be more than adequate for christmas light shows. The sound quality WILL rival any commercial broadcast station.
I have a Visual Basic program that I wrote for it that will program the frequency via the parallel port but the front end could use a little cleaning and a more intuitive GUI (you know us computer geeks write for functionality, not eye-candy) with the input/output port .DLL for access to the outside world (for those that may not know, NT (inc XP) does NOT allow applications to tickle ANY hardware on the host machine, hence the .DLL is needed). If you use an parallel type controller (OLSEN, etc) to control your lights, it could be modified for a serial version that would use the modem control lines to program it. If you use a serial port for VIXEN, then the software will run as is. It can also be programmed via I2C as well. The Visual Basic software is setup for 3-wire. It comes already assembled and ready to go. The only draw back is that it is 3.3 volt - I have an LM317 circuit it could be run from and/or can show the interface from ttl/cmos if these are issues. I had the first one up in about a couple of hours and I was impressed with it.
Here is a link for it....
http://www.sparkfun.com/commerce/product_info.php?products_id=8482

If this has already been mentioned or discussed, I apologize.
This post was generated in the hope that it would be useful to someone -
I am not affiliated with this company in any way, just mentioning FYI...
Thanx

[budude]

That is pretty cool! You could use this in a standalone controller configuration I suppose. I've gotten a couple gadgets from SparkFun before but haven't seen this one - neato!

[Blackbeard]

Can you elaborate a little on what is required to make this work? I reviewed the datasheets, and see the ins/out of the module, but surely there must be more. Does it require frequency setup through the I2C, or could simple switches be used somehow. How about a display? Guess you can tell I'm not geekish enough to probably be asking all this.

steve

[hwrdmltn]

Setting up the module does require programming through I2C or 3-wire. It programs very similar to a serial non-volatile memory or clock chip. Switches could be used if you had a microprocessor in front of it to convert your desired switch settings to the data stream that the chip needs. This is only necessary after each power up. Once the data is programmed, it does not need a constant stream of data - just the initial stream to program frequency, power output, modulation deviation, etc., or to change the current settings to other freqs./settings. This would be an EASY task for a PIC or AVR or ATMEL AT89 series.....if there is any interest, I could put forth a minimal design for a power supply and front end (mcu, switches and/or keypad, leds etc.) using an AT80C2051 or '41 to make it a stand-alone unit. The mcu could also be made so a COM port could be used from the PC. In addition to the Visual Basic version I mentioned earlier, I also have a DOS compiled version that would allow a machine down to an XT with only 640k of memory (wow!) or even one of those early "luggables" that started the laptop revolution to operate it. Get that old XT out of the garage and put it back in service! The user just has to provide an enclosure and the unit can be indoors or out - temperature is NOT a factor in the design of this little guy (they DO NOT use the BHA14 bla..bla.. chip as do so many others, even if they are PLL, drift was STILL a problem with those chips) - this uses a 32.768 khz (not MHZ) time base to generate the frequencies - the same frequency your watch uses to keep time...[OK - rant off]. But one does need EITHER a parallel or serial port (USB to parallel or serial is ok) to tell this chip what parameters you want.

Just FYI in hope that it is useful - I can help anyone out if they are considering this for FM transmitting of their show.

Thanx

[ukewarrior]

I've been building one of these for awhile, but have gotten sidetracked on all the other projects!

Here's the example I'm following. All the code to drive this with an arduino already exists:

http://mikeyancey.com/FM-Stereo-Broadcaster.php

[dmcole]

Can you elaborate a little on what is required to make this work?

Steve:

Let me jump in on behalf of the OP. What he's done is to interface the device to his personal computer, using the serial port to control the NS73M (which apparently needs to have specific data fed to it on a constant basis).

That is a very clever way of skinning this particular feline.

A more traditional approach might be the device built by Mike Yancey, which uses an ATMEL microcontroller (the Arduino) to talk to the Sparkfun board:

http://mikeyancey.com/FM-Stereo-Broadcaster.php

The ARRRduino (as Yancey calls it) ends up costing him about $45-$60 (I don't know that he ever calculates in the cost of the enclosure or the wall wart).

If you Google for NS73M you can find code for the PIC series as well.

My guess is that if some enterprising DIYC member wanted to take on a project, they could create a PCB specifically for our environment, order the boards, have the NS73M premounted to the that board at the factory and bought items in quantity for a co-op, these could be done for around $35-$40 (not including shipping).

\dmc

[budude]

If it had RDS it would be just that much sweeter...

[ukewarrior]

When I have time after the first of the year, this is exactly what I'm planning to do. As I noted, I started but I've run out of time.


Steve:



My guess is that if some enterprising DIYC member wanted to take on a project, they could create a PCB specifically for our environment, order the boards, have the NS73M premounted to the that board at the factory and bought items in quantity for a co-op, these could be done for around $35-$40 (not including shipping).

\dmc

[JFTiger]

I'd like more information on how to connect this to a computer.
BOM, schematics, whatever you are willing to give.

[hwrdmltn]

I'd like more information on how to connect this to a computer.
BOM, schematics, whatever you are willing to give.

Sure - I can bundle it up in a .zip file and attach it (here)?? or can I PM it?

Thanx...

[JFTiger]

Here is fine, PM also.

[hwrdmltn]

Here is an updated zip - I forgot to include the schematics. On the 3.3v interface, if you use 7406 (any variety) the interface is made easy because they are open collector devices - they only produce logic levels to ground hence the need for the pull up resistors which are connected to the 3.3v supply. Obviously this is for 5V logic to 3.3v. The NS73M does not talk back except for 1 logic output that indicates whether the PLL is "locked" or not - not a very useful function since it would only inform a micro that the FM signal may NOT be being transmitted - the PLL might not start if the wrong parameters were programmed or the chip failed.

Just so we are on the "same page", here is the module I was referring to:
http://www.sparkfun.com/commerce/product_info.php?products_id=8482

As far as the connector - the 3.5 mini is ok for a short run, but the rca type (with the correct shielded cable type used) will provide a little better RFI from the harmonics floating around.

On the ant I found that 27" would provide best match - that is cut for the center frequency of the FM band (88-108), but YMMV. I wasn't trying to achieve distance but sound quality. The ant does not affect audio quality unless the power out is so hi and the SWR is through the roof (which is relative to the power output) that it is affecting the local oscillator, so at 100mw even if you have a mis-match, the sound quality will be excellent.

Sorry for all the details. Let me know what else I can help with.

[JFTiger]

Thank you, now I need to get some parts together to power it up and receive an audio signal. I want your opinion on a few things first.

With this is being controlled by a computer, I believe I need a Logic Level Converter.
http://www.sparkfun.com/commerce/product_info.php?products_id=8745

Since this is going to be on a bread board out first, I'm buying breakout boards from Spark Fun. I was wondering if I should use RCA Jacks or the 3.5mm Audio Jack? Since this is coming directly from a computer, I'm thinking 3.5mm Audio Jacks.
RCA http://www.sparkfun.com/commerce/product_info.php?products_id=8826
3.5mm http://www.sparkfun.com/commerce/product_info.php?products_id=8827

Though I've read that a 31” wire is fine with this transmitter, I'm concerned that I may want to try different lengths, or upgrade to a better antenna latter. So I'm thinking of soldering a BNC connecter to the NS73M and switch them out as needed. I also saw that somebody soldered a pin header onto the RF out, I'm concerned about signal loss due to something like this. I've thought of directly soldering the wire to the transmitter. I can later remove it but figured that the act of soldering and removing and re-soldering would eventually damage it.

I also need a power source so I'm debating on the Breadboard Power Supply USB 5V/3.3V Since this is all going to be connected to a computer at all times I figure why not. I also have a USB mini B charger for my cell phone so I'm not going to be completely tethered to the computer.
http://www.sparkfun.com/commerce/product_info.php?products_id=8376

Is there anything else I need? Resisters, Capacitors, etc? I can follow a schematic so if you can share with me how you built and connected yours, I'd appreciate it. Thanks again for the help.

[hwrdmltn]

Here is an updated zip - I forgot to include the schematics. On the 3.3v interface, if you use 7406 (any variety) the interface is made easy because they are open collector devices - they only produce logic levels to ground hence the need for the pull up resistors which are connected to the 3.3v supply. Obviously this is for 5V logic to 3.3v. The NS73M does not talk back except for 1 logic output that indicates whether the PLL is "locked" or not - not a very useful function since it would only inform a micro that the FM signal may NOT be being transmitted - the PLL might not start if the wrong parameters were programmed or the chip failed.

Just so we are on the "same page", here is the module I was referring to:
http://www.sparkfun.com/commerce/product_info.php?products_id=8482

As far as the connector - the 3.5 mini is ok for a short run, but the rca type (with the correct shielded cable type used) will provide a little better RFI from the harmonics floating around.

On the ant I found that 27" would provide best match - that is cut for the center frequency of the FM band (88-108), but YMMV. I wasn't trying to achieve distance but sound quality. The ant does not affect audio quality unless the power out is so hi and the SWR is through the roof (which is relative to the power output) that it is affecting the local oscillator, so at 100mw even if you have a mis-match, the sound quality will be excellent.

Sorry for all the details. Let me know what else I can help with.

[JFTiger]

I'm stuck again. Mouser doesn't have the 7407 you susgested. So I went to town and got the parts for a PIC controled transmitter based on this web page.
http://www.creativewidgetworks.com/cww/index.php?cat=PIC&art=80
Should have got the 7407 at the same time. But I can't prove its working or not. Probablly because I didn't connect a descent length of wire to it yet. My questions are, does it need to be solid wire? I also found my wifes old stero and was able to remove the antenna from it. Can I use this also? Its collapasable and it extendws to about 18". The antenna on this Ramsey looks like it.
http://www.ramseyelectronics.com/largepic.asp?image=FM30B

[hwrdmltn]

OK - mybad....you can use a 7407, 7417 or any open collector type TTL chip.

These are available from here:
http://www.futurlec.com/index.shtml

The PIC is ok too - I did my other in an AT89 series for standalone operation (I don't have it documented yet) - I'm just not a fan of the MICROCHIP PIC programming model so I tend not to have too much to do with them although if you use a PIC, I would be interested in seeing your design.