Data on 12V supply wires
in [Design]
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From: James on 2 Aug 2010 05:13 Hello, I want to send half duplex digital data - moderate rate, say 1k bps or a bit faster - on a 12V, 2 wire, supply cable a few tens of metres long. It is to connect a remote sensor to the user's display unit, both portable. The parts need to be fairly small (eg a chip and a few resistors). I was hoping to be able to find a chip that will generate a modulated signal, that could be connected to the supply cable. But I haven't been able to find a chip that's designed for this. Please can anyone suggest anything? James
From: Grant on 2 Aug 2010 05:31 On Mon, 2 Aug 2010 10:13:28 +0100, James <nospamplease(a)nonsuch.com> wrote: >Hello, > >I want to send half duplex digital data - moderate rate, say 1k bps or a >bit faster - on a 12V, 2 wire, supply cable a few tens of metres long. It >is to connect a remote sensor to the user's display unit, both portable. What are you sensing? The standard industry method is 4-20mA current loop, can be stretched to 10-50mA. The low end is the circuit quiescent current, the high end is max signal. Supply with unregulated 20v to 40V depending on loop V drop. At the sensor end, a 5V or 12V zener gives you local supply voltage for electronics, then you modulate the current to indicate the reading, 4mA for zero, 20mA for full scale. Examples in LM10 opamp.reference datasheet and AN201, and other older opamp cookbooks. > >The parts need to be fairly small (eg a chip and a few resistors). I was >hoping to be able to find a chip that will generate a modulated signal, >that could be connected to the supply cable. But I haven't been able to >find a chip that's designed for this. Please can anyone suggest anything? Single opamp and a power transistor or MOSFET, plus signal conditioning and a zener for power, quite easy. Depends what you measuring. Grant. > >James
From: James on 2 Aug 2010 06:54 On Mon, 02 Aug 2010 19:31:56 +1000, Grant wrote: > On Mon, 2 Aug 2010 10:13:28 +0100, James <nospamplease(a)nonsuch.com> wrote: > >>Hello, >> >>I want to send half duplex digital data - moderate rate, say 1k bps or a >>bit faster - on a 12V, 2 wire, supply cable a few tens of metres long. It >>is to connect a remote sensor to the user's display unit, both portable. > > What are you sensing? The standard industry method is 4-20mA current loop, > can be stretched to 10-50mA. The low end is the circuit quiescent current, > the high end is max signal. Supply with unregulated 20v to 40V depending > on loop V drop. > > At the sensor end, a 5V or 12V zener gives you local supply voltage > for electronics, then you modulate the current to indicate the reading, > 4mA for zero, 20mA for full scale. Examples in LM10 opamp.reference > datasheet and AN201, and other older opamp cookbooks. >> >>The parts need to be fairly small (eg a chip and a few resistors). I was >>hoping to be able to find a chip that will generate a modulated signal, >>that could be connected to the supply cable. But I haven't been able to >>find a chip that's designed for this. Please can anyone suggest anything? > > Single opamp and a power transistor or MOSFET, plus signal conditioning > and a zener for power, quite easy. Depends what you measuring. > > Grant. >> >>James Yes, that seems like a good way to do it. For data going from the display to the sensor I'm thinking of varying the supply voltage - say by about 0.2V. Then current variation at the sensor for data going the other way. I was hoping for something ready-made that would use modulated fsk data or similar - like a wireless system, but using the supply cables. I don't want to use a real wireless system because the probe is buried. James
From: Paul Keinanen on 2 Aug 2010 08:12 On Mon, 02 Aug 2010 19:31:56 +1000, Grant <omg(a)grrr.id.au> wrote: >On Mon, 2 Aug 2010 10:13:28 +0100, James <nospamplease(a)nonsuch.com> wrote: > >>Hello, >> >>I want to send half duplex digital data - moderate rate, say 1k bps or a >>bit faster - on a 12V, 2 wire, supply cable a few tens of metres long. It >>is to connect a remote sensor to the user's display unit, both portable. > >What are you sensing? The standard industry method is 4-20mA current loop, >can be stretched to 10-50mA. The low end is the circuit quiescent current, >the high end is max signal. Supply with unregulated 20v to 40V depending >on loop V drop. To transfer some digital information in addition to the analog 4-20 mA measurement, the HART protocol could be used. Alternatively, take a look what has been used in various power line communication systems are using. Anyway, the problem is how to inject and extract the data signal to the DC or LF AC power signal. Typically transformers are used, with the DC power flowing through a few turn primary and the signal connected to the multiturn secondary. The signal should not contain any DC components, so direct UART connection is not usable, but Manchester coding could be used. FSK or On/Off keying could also be used. Keying a 567 PLL on the transmitter side and using an other 567 PLL as the receiver might work. For 1 kbit/s data rate run the PLLs at 50-500 kHz.
From: Scheini Karl on 2 Aug 2010 12:59
On 2 Aug., 11:13, James <nospample...(a)nonsuch.com> wrote: > Hello, > > I want to send half duplex digital data - moderate rate, say 1k bps or a > bit faster - on a 12V, 2 wire, supply cable a few tens of metres long. It > is to connect a remote sensor to the user's display unit, both portable. > > The parts need to be fairly small (eg a chip and a few resistors). I was > hoping to be able to find a chip that will generate a modulated signal, > that could be connected to the supply cable. But I haven't been able to > find a chip that's designed for this. Please can anyone suggest anything? > > James Hi James, maybe an MBUS could help. But you have to double the 12V. Pls see: http://www.m-bus.com/files/MBDOC48.PDF http://www.m-bus.com/default.php Regards Karl |