Post by thread:[EE:] Simple digital FM transmitter/receiver pair

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

> > 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

>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

{Quote hidden}> > On Oct 13, 2007, at 6:39 PM, Brendan Moran wrote: > >> 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 Okay.... what about the other questions ? Cedric

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Brendan Moran wrote: {Quote hidden}>> 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 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 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (MingW32) iD8DBQFHE4VxkA9dCbrNdDMRAtYqAJ4xRuuzCJxcf1mVIJqXzberyKzt8ACfdg86 EJf2qyDbYRn+TXM8lK+xvNo= =RSFY -----END PGP SIGNATURE-----

> 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?

>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

>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.