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'[EE:] Simple digital FM transmitter/receiver pair'
2007\10\13@191355 by Brendan Moran

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Hi,
I want to build a paired FM transmitter/receiver that encode UART data
onto a signal line that goes through a very noisy/lossy environment.
I'm looking for a simple pair of circuits because they need to be very
small.  So far, I think that a simple oscillator based on a variable
capacitance diode would work well for the transmitter, but are there any
simple hacks that can be used for receiving digital data over FM?

Thanks,
Brendan

2007\10\13@195416 by Cedric Chang

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>
> On Oct 13, 2007, at 5:13 PM, Brendan Moran wrote:
>
> Hi,
> I want to build a paired FM transmitter/receiver that encode UART data
> onto a signal line that goes through a very noisy/lossy environment.
> I'm looking for a simple pair of circuits because they need to be very
> small.  So far, I think that a simple oscillator based on a variable
> capacitance diode would work well for the transmitter, but are  
> there any
> simple hacks that can be used for receiving digital data over FM?
>
> Thanks,
> Brendan

Why FM ?  there are other technologies that are more easily applied.  
What distance do you want to transmit ?  What data rate ?  Do you  
want to transmit in both directions ?  Any chance of interfering  
units being nearby ?

Best

Cedric

2007\10\13@203927 by Brendan Moran

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>Why FM ?  there are other technologies that are more easily applied.  
>What distance do you want to transmit ?  What data rate ?  Do you  
>want to transmit in both directions ?  Any chance of interfering  
>units being nearby ?

>Best

>Cedric

First, I'm going to to be transmitting over a conductor, so antennas are
not an issue, and I can easily use any frequency.

I want to use a modulation technique because the data is going to be
multiplexed with a power rail.  I expect the power rail to be pretty
noisy, as it will have feeds to brushed DC motors.  AFAIK, AM is
susceptible to noise generated arcing, and FM is less so.  That is why I
wanted to use FM.

Thanks,
Brendan

2007\10\14@160604 by Cedric Chang

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{Quote hidden}

Okay.... what about the other questions ?
Cedric

2007\10\15@112123 by Brendan Gillatt

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Brendan Moran wrote:
{Quote hidden}

Have a look at the Exar XR2211ACP-F

- --
Brendan Gillatt
brendan {at} brendangillatt {dot} co {dot} uk
http://www.brendangillatt.co.uk
PGP Key: pgp.mit.edu:11371/pks/lookup?op=get&search=0xBACD7433
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2007\10\15@115147 by Alan B. Pearce

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> I want to use a modulation technique because the data is going to be
> multiplexed with a power rail.  I expect the power rail to be pretty
> noisy, as it will have feeds to brushed DC motors.  AFAIK, AM is
> susceptible to noise generated arcing, and FM is less so.  That is why I
> wanted to use FM.

As you have already stated that this is for model railway application, why
not just go with the proposed NMRA standard?

2007\10\15@123631 by Brendan Moran

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>As you have already stated that this is for model railway application, why
>not just go with the proposed NMRA standard?

I have a few reasons.
1)Running a non-DCC engine on a section of DCC track is prone to causing
overheating in the engine.
2)There is no practical method for an engine to send data back to the
controller using DCC.
3)Where's the fun in that?

Regards,
Brendan

2007\10\15@142206 by David VanHorn

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National made some powerline modem chips running at 250kHz and 300kHz
IIRC, I used them at one point for data ghosted over internal PBX
phone lines, but they were designed to talk through a safety
interface, over 110/220 power lines, so I think they could handle
railroad power ok.

2007\10\15@151921 by Dario Greggio

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Brendan Moran wrote:

> 3)Where's the fun in that?


Hi, I may be interested in something similar, in the near future (say 6
months - moving to a new home).
And I agree on your point :)

--
Ciao, Dario
--
ADPM Synthesis sas - Torino
--
http://www.adpm.tk

2007\10\16@055542 by Alan B. Pearce

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>1)Running a non-DCC engine on a section of DCC track
>is prone to causing overheating in the engine.

Well, I cannot see what it is you are attempting to achieve if you are
running an analogue loco with feedback. How is the feedback circuit going to
be powered when the loco is stopped?

And only a handful of DCC manufacturers have implemented the analogue loco
operation under DCC, as it is an optional feature. Any overheating in the
motor is dependant on what sort of motor it is, - and you certainly would
not want to be using a coreless motor in this mode.

>2)There is no practical method for an engine to send
>data back to the controller using DCC.

Yes there is, the NMRA does have a proposal for doing exactly this.

>3)Where's the fun in that?

Well, I could say the same about your apparent attempt at re-inventing the
wheel. There are more useful things to do in life, by building on the
already existing facilities.

However another method you may wish to think about, if still interested in
pursuing this, is the chip that is used in the Marklin system for their mfx
locomotives. The data stream is sent back as some form of higher frequency
carrier, and then in the control unit they demodulate it using a standard
RDS receiver chip. This then attaches to an SPI port on the micro in the
control unit, with the RDS chip recovering the clock and data and applying
both to the SPI port, which is therefore acting as a slave device. I do not
have any information on the RDS stream format, but based on this I assume it
is some form of NRZ that allows the clock recovery to be done.

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