Communication over DC Bus at low data rate

Question

I am looking for a solution to modulate a data signal into a DC powerline that has 12-60V. I found for example the DC-Bus solution from Yamar. But they are the only ones offering this and their chips are 5$+; even in high quantities. That's too much.

I read somewhere that I could use a coupling capacitor. But then I whoud still need to know how to it like that and how I modulate it best (I know what a coupling cap is tho; even tho I don't really get how I would do that yet)

If there is an easy and cheap solution to implement without a full IC, I am glad to hear about it too :)

Any advice is appreciated, even if it's just Kewords I can google about.

The data rate should be in the kbps range. Mbps is nice but by no means needed!

And yes, there is really only that way of doing it. RF is no option and additional wires too.

Edit1:

The data I want to transmit is a voltage of a solar panel every few seconds. So as you can see, the data is not very vital and if I wanted to increase reliability I could just transmit the voltage twice.

Because multiple panels are in series , I thought of a master that announces which panel can "speak" next.

I thought maybe it's easiest if there is like two different frequency levels. one for the master to say whos turn it is and one for the actual voltage. So e.g: base indicating frequency is 100khz. Each khz more is +1. so if the master modulates in 100kz that means panel 0 should speak, 101khz means panel 1 etc. Same would go for VTG: base frequency could be 10khz and each additional khz could means +1. so eg. 12V is 10khz, 13V is 11khz etc.

I don't know how stupid or difficult that actually is compared to serial methods :)

I used RS232 for a lot of projects yet even tho I wouldn't say I understand the protocol itself to it's farest extents. I would say I know the basics (+3 is logical zero, -3 is logical 1, There is a start bit synchronizing the clock and a stop bit I don't understand exactly what it is for other than a minimum of one bit pause between two bytes :).

Thanks in Advance!

Answer 1

This approach is common in industrial control systems such as AS-i.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Power and data on the same wire.

Here is a simple idea that meets your criteria and might even work!

• Problem 1 is to make the DC circuit high impedance to your data signal. This can be achieved by adding a series inductor to each power feed and tap-off. You need to calculate the inductance based on the frequency of your data signal and how low an impedance your data signal can drive and still be readable by the receiver.
• Problem 2 is to superimpose the data signal on the line. AC coupling should suffice for that. Again, you need to calculate the capacitor value based on the data frequency and load impedance.

Note that since the transmitter is most likely to be in the same location as the PSU that L2 could be omitted and the transmitter powered directly from the battery.

All loads on the line, including the receivers, will need a capacitor between internal V+ and GND to minimise feeding switching transients back onto the P+D (power + data) line.

You have a bit of work to do but judging by your question you have time but not money. ;^)