Data and Power Transfer

The data rides on top of the DC voltage. Essentially, what you have is an AC component riding on a DC voltage:

The receiving circuit separates the AC from the DC and reads it as data.

Vulcan, IMHO, great answer - right to the point!!!

Thanks Vulcan,

But actually what i want to know is that RS 485 requires 4 wires in case of master and slaves are using same power source or other methods are like AS interface, LIN, CAN etc. how to achieve this and by using what technology and components. if you help me i will be thankful to you.

Hitender Kundu

Daksh Electronics Pvt. Ltd.

E-mail : h_kundu@dakshglobal.com

Phone 91-11-9871047979

In RS 485, it is not expected that the power for the slaves will be provided by the master. It is possible to use a single power supply for more than one nodes, if it is convenient. But various nodes are expected to be at large distances.

Hello Hitender, welcome to CR4.

Was that you who posted the original question? I'm asking because the question you're asking now is very different from the original question.

Are you asking if you can use the existing RS485 wires to provide power to your other nodes while still serving as the data transmission cable?

Hmm, that's a pretty project you've undertaken. I've checked B&B Electronics website and they have something that may interest you. If you wish, you can contact them about your problem and they can even custom make something for you.

If you want to do it yourself, I can give you a suggestion that you can experiment on but I can't guarantee the result as I've never done this myself.

of cuase you can!

many instances in application in industry control and communication. even more hv, like 220 380v line etc.

8 bits can management 256 slaves sets.

24 VDC is a bit high, but the model railroad hobby uses a Digital Command and Control (DCC) system to control up to as many locomotives running on the rails (2 rails) as can be identified by 4 digits. The signal is sent as pulses of AC power by the command station and each locomotive has a decoder mounted inside. Boosters are used to raise the amperage available. You might look up the manufacturers of the many systems on the market and discuss your problem with them.

As vulcans scetch shows your data is riding on a dc level. Transmitting data in this way is an approved technology working well with your 256 slaves and over a distance of several hundred meters. If your 1200m can`t be reached you should use a converter which receives and again gains your signal.

To get an idea of how this can be done, have a look at the well documented HART-protocol. This was once developed for 4...20mA interfaces sending an analog current to analog panelmeters but can also be modified for data transport upon 24VDC lines. But have a look at load spikes initiated by your supplied slaves - your supply has to be filtered very well after coupling out yor data. As the data frequency is high enough the receiver "sees" only the integrated dc current while the information sitting on the dc level is coupled out.

www.analogservices.com/about_part0

gives detailed informations about the technology and you can get an idea of what kind of data shall be transmitted, what are the basic problems, how can I isolate a modem etc.

Hope that helps
Regards Uwe

Try out 1-wire communication devices. These carry power and signal in both ways and you can hook large number of devices.

www.maxim-ic.com/

Also try using 4-20mA type link.