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ASFK/Bell 202

Chuck Mathews
Prodigy 10 points

Other Parts Discussed in Thread: CC1101

I'm looking to do an APRS implementation and think that the MSP430 may be the perfect chip, but I'm not figuring out everything I need from the datasheet.

The plan is to use the RF frequency of the MSP430 as an intermediate frequency and use an RF mixer to obtain the desired frequency in the 2-meter amateur radio band. I don't see any reason this should not work with this chip, but do you know if anyone has tried anything similar in the past?

Also, I need to know if I can output the Bell202 standard ASFK using 1200Hz for binary 1 and 2200Hz for binary 0. The required transmission speed is 1200 bps appears to be well within the capabilities of this chip.

The other question is whether the chip can handle collecting sensor inputs (such as temp probes and GPS receivers) and saving this information to memory while transmitting or if I will need a second microprocessor to handle this and pass it along to this chip when it is not transmitting.

 

Thanks in advance!

 

Chuck

  • 0
    Guru 12160 points

    Hi Chuck,

    Your idea sounds interesting but were you planning to use a square wave coming out of the MSP430?  If so, you will almost certainly need to re-shape it with external hardware before you let it get to the mixer.  If you mix it as a square wave I think you will clobber adjacent channels and all kinds of out of band frequencies too.  It will be a spectral mess.

    However, if you choose an MSP430 model with a built-in DAC and a DMA controller, it can generate a 1200Hz wave and a 2200Hz wave as long as you provide the right reference clock.  With this approach you could shape the signal much more easily (just with RLC stuff).  Then you could modulate data at 1200 bps by switching between the two outputs as necessary.

    As for the data sheets, keep in mind that MSP430 products live and die by two documents, not just one.  The so-called data sheet has processor-specific information and is typically tens of pages.  The family user's guide is hundreds of pages long and covers the entire family (eg, MSP430x1xx, MSP430x2xx, MSP430x5xx, etc).  Both documents are available from a particular MSP430 model's landing page on the TI website.

    And yes, the chip can handle all kinds of sensor inputs and can save, process, and stage it for transmission.  You wouldn't need two MCUs.  You can even connect it easily to an external flash memory like SPI NOR flash at 16MB for simple "large" storage.

    Jeff

  • 0
    Guru 227245 points

    Talking about 'the MSP' is like talking about 'the Chevy'. Without knowing what car model you have, the discussion is meaningless. There are ~340 different MSPs.

    However, you're talking about RF frequency. So I assume you mean an MSP from the CC430F513x, 612x or 613x sub-family. If so, these devices have an RF frequency range from 300 to 928MHz. So I don't know how you want to use a mixer to put the output into the 2m band.

    Nevertheless, there are three documents you might want to read: teh 5x family users guide, the device datasheet and the CC1101 RF transceiver datasheet (which is the base for the MSP-internal RF transceiver)

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