2 wire control(communication) and remote voltage supply?

Mike picking away · Guest

I am looking for direction or resource help with trying to do the following. I want to use a 2 wire comunication scheme to a remote control module. This module would get its comunication and voltage supply from the same 2 wires. I know this is being done and don't want to reinvent the basic design. Any ideas, help, or direction would be appreciated.

Mike

Neutone · Joined: 08 Sep 2003 Posts: 839 Location: Houston

How much power do you need to supply? How fast do you need to comunicate? Is it going to be bi-directional comunications?

Really, you need to discribe your application in greater detail.

dyeatman · Joined: 06 Sep 2003 Posts: 1933 Location: Norman, OK

What you are asking is a circuit design issue and really has nothing to do with the PIC or CCS C and you really need to go somewhere like the alt.electronics newsgroup with this problem to get the proper support and guidance in attempting this. Especially if you dont have an electronics theory background you definitely want to get experienced electronic help. I am an electrical engineer, it took me almost 6 months to get a stable final design completed and it took a quite a bit of trial and testing to get it right. Unfortunately , due to the design being proprietary to the company I work for I cannot give design details.

I have done this for distances up to 700 feet so far with several different types of systems/processors and it has worked well.

Basically you isolate the PIC UART I/O pins and the comm circuit connections on the other end of the cable from the cable wires themselves using a blocking capacitor to block the DC voltage. You inject the DC (say 9-12 VDC) at one end and pick off the voltage for the PIC at the other in between the two blocking caps. The cap values will be totally dependent on the frequency and comm protocol (RS232, I2C CAN etc) you will be wanting to use.

On the PIC end you must use a regulator to provide power stabilization due to voltage drop in the cable.

Guest · Posted: Sat Jun 12, 2004 10:35 pm

Thanks for the input. I am also an electrical engineer (senior design). I understand perfectly what you are saying. The reason, as you pointed out, is that it takes time to perfect a circuit and I didn't want to reinvent the basic wheel agian.

Also point taken about my question relating to a electrical design. I can make this sort of scheme work with an 8 bit motorola chip, but want to do this with the PIC 16F877A. The code is a little tricky because of the timing and mixed signal seperation. I was thinking of using a charge pump device and running 10kHz constant signal as the carrier and possibly using zero crossing or a rider to send messages.

agian, thanks for your input
Mike

Guest · Posted: Sat Jun 12, 2004 10:43 pm

dyeatman · Joined: 06 Sep 2003 Posts: 1933 Location: Norman, OK

Well Hello Mike! Very glad to meet a fellow engineer online!

My implementations are all 2400 baud. Going beyond that at the time posed significant hurdles I chose not to cross and kept things pretty simple from a design and maintenance standpoint.

Nowdays, if you go AC, a quick and very simple implementaion is the AC ethernet network modem which is widely available and you can get 5+ MB per second out of them pretty reliably and save a ton of time and money on design and debug.

Another is the powerline phone extension modems which can give you up to about 30KHZ or so I believe and those are cheap on EBay. On both of these the distance is somewhat limited but should give you what you need, but hey the whole thing can run on zipcord!

When I built my circuit those were not available :-( or I would have definitely gone that route and saved a lot of headaches!

Like you I started with the Motorla 6800 (remember MICBUG?) then the Z80 years ago and later graduated to the 68000 and X86. Then found the PIC and fell in love with it. Very few of my designs require capabilites I cannot meet with a PIC and over 90% of my creations are now based on them.

CCS C and the PIC have worked quite well for me over the last 3 years or so.

Good luck!
Dave

loh · Joined: 14 Jun 2004 Posts: 3 Location: Taiwan ROC, Taipei.

Hi

I am a begining engineer, have doubt on pic16f84 detect signal coming in from IR. A direction or code would be appreciated.

Should I check register flag? which one if so?
Should I check interrupt acitivity?

the pic takes 5V @ 4MHz. I/O pin draw from IR.