| Electronics > Beginners |
| Serial Over Long Wire Run |
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| C:
David Hess Was not picking on you. I think it is safe to say that most think first of voltage. Think this is sad. Is it a loop or single ended. There have been telephones with only one wire with earth the return. Just think a telephone is a very good example of what you can do with current based system. Here you provide power, signaling and full duplex audio. As for rare, could be how you look at it. You have many things that very the resistance. At a distance using current change can give better results then voltage. I have seen and used current based systems often. Back in the 80's, HP built a pressure sensor for use in the oil field. It was attached to wire line often up to 15,000 feet long. Wire line for those who do not know is a braided steel cable with an insulated conductor in center for signal built to lift a load(often in 100's or 1000's of pounds). Yet with this poor connection, supplied power to pressure sensor which had an output of 0-15,000.00 psi. Yes to 100th of pound. The wire line was often 15,000 feet long and the pressure sensor could be working at 200 C. A current change was used to transmit. That 200 C might sound high to people here, but very limiting in wells. Last I looked they were up to 350 C and keeping the smoke in. Normal solder and plastic packages do not survive, chip might. ===== Any way Op's problem for 100 feet can be easy with many ways to cure problem. But if I was Op putting an atmega in the window controlling LED strips, I would use part of that compute power to verify proper operation. Failure to check proper operation can lead to embarrassing problems. C |
| Seph.b:
Wow, thanks everyone for the wealth of information. This definitly gives me plenty of options. Luckly it is just important to get the LEDs in the windows now and I have some time to work out the control. |
| Seph.b:
The MAX485 really looks like the way to go. |
| Eka:
Power your 18 awg wire using 48 VDC, then use a DC to DC converter to change it to 5VDC at the window. Wide input range DC to DC converters are available for reasonable. You'll need some big input capacitors because the input is highly inductive. As for the signal. Almost any differential line driver pair can do 100 feet. If you are running small amounts of data over the link, then RS485 drivers will do. If you want to push a lot of data, then look at using ethernet. Put a smart ethernet NIC on the atmel. There are smart ethernet interfaces that will sent the data from the packets serially on to the atmet. All the atmel has to do is do a small bit of configuring, then receive the data. No ethernet management duties. If the amount of watts you need for the LEDs is low enough, then POE may work, but my guess is that isn't enough. I can't power my LED art with POE links. For all my LED displays that are remote, I use a Raspberry Pi with built in WIFI to communicate to them. The APA102 based displays are directly driven by the Raspberry PI. I just need to find a power source at the display site, and give the Raspberry PI the SSID for the network. That can be written to the right files on the microSD card before putting it into the Raspberry PI. I use 48VDC over 18 to 12 awg wire from the nearest wall outlet to power them. With high line losses they can be a few hundred feet from the power supply. I try to stay under 40 feet for efficiency. |
| Seph.b:
We are going to run 12v over the 18awg wire, probably measure it at the end and adjust the voltage to be right at 12v. I just use 7805s for the 5v to run atmegas. I know it is not as efficient as a switch mode, but they are cheap and quick. |
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