I'm in the process of implementing some simple control nodes (just switches) and looking for the simplest (cheapest) network protocol to use. To date, LIN bus seems to be the best candidate. I need very low speed, high reliability and low off-board distance (a few up to
10s of feet).
Ideally, something that could be two wire with power and data combined would be ideal, so that the power could be distributed to power the slave nodes. LIN is good, but it requires a 4 wire (or 3 I suppose) interface.
I looked at ASI (Acuator Sensor Interface), but not sure how practical it is.
You could always go analog. Each switch has a series LC network, and the control circuit just imposes a small AC frequency over the network, and looks at the impedance. The plusses of this are of course you only need one real circuit, the others can practically be built onto a chocolate block.
I looked there, but couldn't see anything related to multi-channel control over the DC supply wires.
I have a pal who (in later life) is resurrecting his interest in model railways. Apparently there is now some reasonably standardised method of multi-device control via the DC supply through the rails. Trains, points and signals can all be controlled via one DC supply. It is supposed to be popular in the US model engineering market, but he hasn't been able to find out any technical details yet.
I thought someone would mention this eventually. It's called Digital Command Control (DCC) and is maintained by the National Model Railroad Association. The NMRA standards are at
There are a lot of manufacturers world-wide that make the various mobile and staionary decoders, booster/command stations, hand-held throttles, computer interfaces, etc. Note that the standard only applies to the booster to decoder side, while the booster / throttle / computer network tends to be proprietary to each manufacturer. Most of the modelers I know use Digitrax
I don't think that DCC is suitable because it looks they reverse the polarity on the rails or some crazy thing. The Siemens ASI seems to be it. It uses a simple unshielded two wire data+power cable and the network can be up to 64 slaves each of which can be multiple I/O. Noise immunity is achieved by superimposing a narrowband sinewave that is modulated by something called APM= Alternate Pulse Modulation- of just exactly what-phase, amplitude, or something else-I don't know, but the slave receivers require crystal timebases. The ASI has been around for
10 years now so that it is well-developed and supported- you can tie it into almost any other industrial control bus, or PCI, or VME, or whatever- and there are plenty of chipsets available for building a product from scratch too. It has quite a bit of protocol overhead so that custom development would not make sense unless you're building a compatible product for market- an in-house actuator control bus should use readily available off-the-shelf modules from any one of dozens of manufacturers.
Yes and sold it to someone. The circuit was a little different because we used an LT1081 to make the signal from the micro bigger and stronger and attempted to cancel the self signal (the micro hearing its self).
It was about 100% for one side only transmitting. The self signal cancelation was a bad idea. It is better, if you can, just to only have one side talk.
DC component of 9/10th signallig voltage will be stripped (too bad)
1st harmonic of BR/10 and everything above will be carried over. The recessive state will be negative, the dominant state will be slightly over ground. Microcontroller would not receive correct data unless DC component is restored.
As for restoring DC component, one example I can think of is if R2
Hello, You could also look into a company called Yamar (
) who makes chips that communicate over the DC power lines using the LIN bus. Soon there will be modules that can implement 250K CAN bus. They are not very expensive. You can follow the electric car charging standard. Once this is final then I imagine more suppliers will be making parts. If you want data and power then look into a company called PowerByProxy out of NZ. This is more expensive.