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Author Topic: Can some one help me with a PCB layout?  (Read 2423 times)
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Here is a rendering of the finished board.


* rs485.png (19.35 KB, 676x419 - viewed 17 times.)
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The layout looks good.
I think your 22uF cap model may be a little too big.
Compare that to this 100uF, 16V cap which can be seen to be about 0.15" wide, versus what looks like twice that.

5mm actually, just measured it.
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Thank you.  I am a little bit confused on the capacitor size.
The data sheet says .22uf for in and .1uf for out.  However the normal values I see on line are 100uf in and 10uf out.

Here is an updated version that would let me use ether or both size capacitors.


* rs485.png (27.64 KB, 924x545 - viewed 14 times.)
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I have looked at many manufacturs data sheets for 7805s, and all show 0.33uF on input & 0.1 on the outout.
Bigger will not hurt.
The physical size of the parts will vary.
I just finished making 12 boxes, half had 12V sourced over 40-50 foot cable.  I used 1uF on the input and 0.47uF on the output, that's what I had on hand, worked just fine. Neither were physically big as the your model has.  If the board can take a large part like that, than a smaller part would certainly fit.

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This board allows me to send some signals (in this case clock and data to an LED display) long distances and to multiple locations.  I am also sending 12V power down the wire as well.

The IO pins on the Arduino and other logic chips are only made to drive signals a few inches on a circuit board.  The max485 chip we are using here can take those signals and convert them to an RS485 hardware layer.  RS485 is good for several thousand feet and driving 30+ slave units.  You can read more about RS485 on wiki and a few other pages, it has been around for a VERY long time.

I also added a 5V regulator so I can power the max485 chips and some external devices I use that are 5V only.  If you have any more questions just ask.

ok but what's the practical use of it? Give me some example on what I can do with it?
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Unfortunately this was a first attempt with the software I picked to try first.  I looked at my random capacitor drawer and it looks like most have one of 2 or 3 lead spacings.  I have no idea what form the 3d rendering is using but I am pretty sure I can fit any capacitor I would need with the holes I have.  I am also considering the possibility of  2 capacitors in parallel on the in and the out.  I added a second set of holes to the output as well, both of those are narrow.  I also got the feeling it will not really matter what values I end up with.

Thank you for looking!

Latest image attached.
 


* rs485.png (28.04 KB, 924x545 - viewed 10 times.)
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@polishdude, go look at reply #2. Circuit is to send buffered signals down long wires.
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ok but what's the practical use of it? Give me some example on what I can do with it?

In my case I am putting large LED displays throughout an auction house.  Each display needs 2 signal lines.  This board takes those signals from the Arduino pins and converts them to signals that can travel hundreds of feet down cat5 AND to multiple locations.

Other uses I have in mind are DMX output from Arduino and connecting 2 Arduinos several hundred feet apart.
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ok but what's the practical use of it? Give me some example on what I can do with it?

In my case I am putting large LED displays throughout an auction house.  Each display needs 2 signal lines.  This board takes those signals from the Arduino pins and converts them to signals that can travel hundreds of feet down cat5 AND to multiple locations.

Other uses I have in mind are DMX output from Arduino and connecting 2 Arduinos several hundred feet apart.

ok so basically through a few wires the whole LED display signal is carried? that's pretty cool. what are those ICs you use?
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From post #1: "board that holds 2 max485 chips, termination resistors and a 12V to 5 V regulator"

You will send a serial message containing the data you want to display, which a processor on far end will display.

Or I suppose if you ran enough wire you could do it without the processor, just drive a buffer that drives the LEDs on the other end...
« Last Edit: March 13, 2011, 06:22:29 pm by CrossRoads » Logged

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The IO pins on the Arduino and other logic chips are only made to drive signals a few inches on a circuit board. 

Really?  I was going to use the Arduino to excite a sensor that's at the end of a 10 foot wire that requires 5v at 5ma.  Can I not simply attach the sensor excitation wire to one of the digital output pins of the Arduino and write it high in order to excite the sensor, or do I need a separate relay or opto that's triggered by the Arduino that feeds the sensor 5v from a regulator?
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If you're only putting 5V out at a DC level, you'd probably be okay.
Are you getting data back from the sensor too?
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I am going to give that one a maybe.  It depends on the impedance of of the sensor, wire, and IO pins.  It also depends on how much electrical noise there is in your area and how reliable it NEEDS to be.  With out knowing what your sensor is I have no idea if my board would even work.  It is digital only.

In my case I have to go long distances and I can not have interference.  Also DMX lighting instruments require an RS485 feed.
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