RS 485 wireless communication

[Ron Marcus]

Can you hook up the PICs directly to the 232 side of the 232 to 485 converters? At least this will prove it is a problem with the TI part. It would bite if you got the Max parts and found out it was something else! I replaced every part on an RF comm board (including connectors!), to find out I mixed up the RTS and CTS lines in my code. That was five hours better spent elsewhere. "The length of time debugging is directly proportional to the stupidity of the error." This I have gleaned from personal experience.
Ron

[Armadus]

Ron,

Which of the Maxim RS 422 converters do you use?

-Greg

[Ron Marcus]

I used the MAX 487. It is simplex though, but tough as nails. Only one external resistor, and the obligatory .1uF bypass cap.
Any luck with the module? I am using the AC4490 out to a mile with 1/4 wave whip. It is a direct connect to the PICs UART.
Ron

[SergioRM]

Did you try use a pull up or pull down resistor on the RX pin?

Regards,

[Michael]

I'm curious about the ultimate outcome on this as I'm having the same problem
and although I'm using RS232 right now (at only 1200 baud)....the goal is to use RS485, which is how my hardwired boards are set up.

My hardwired pic to pic is fine but the (LINX) wireless has some problems that at this point, I'm attributing to noise.

I've tried to fix it in software but no luck.

I thought of buying a pair of Maxstream Xcite modules but will hold off? until I see what happens here.

I thought with the Maxstream or Aerocomm products, it may be a simple plug and play.

I think designing a system based on the LINX modules might be more than I bargained for.

[Dave]

Michael, I have personally used the MaxStream 900 Mhz. modules with great success at over 7 miles. I use them to control an Amateur Repeater control functions of a signal to noise voting system. I highly recomend them to any body wanting reliable communications at 19200 baud.

Dave Purola,
N8NTA

[Michael]

I know they make some hi powered units (good for miles) but was looking at the bottom end "Xcite" oem modules for indoors.

Of all the RF stuff out there, I think they look very impressive and very reasonably priced.

I'm wondering if the whole matter of RF data isn't meant for my soldering iron and better left to the experts.

[Ioannis]

[QUOTE=Michael]I'm curious about the ultimate outcome on this as I'm having the same problem
and although I'm using RS232 right now (at only 1200 baud)....the goal is to use RS485, which is how my hardwired boards are set up.QUOTE]


Have you implemented few bytes of preamble and also Manchester encoding to your software?

The first is absolutely necessary to stabilize the data slicer at the receiver end. The second mainly depends on the modules. Does not hurt if you can tolerate speed (you actually send 2 bytes for 1 data).

Ioannis

[Michael]

Don't laugh but I'm not sure about how a data slicer functions.....I do have a squelch circuit that controls an analog switch that I will "assume" is a "data slicer" (pass--no pass?). ??

I have 2 qualifiers in my serin statement and then 2 data bytes that follow.

What seems to be happening is I have a sequence at the very START of the program, that shouldn't function unless a switch is pressed.

It is going through the routine at the rcvr end anyway and the only thing I can figure out is that rather than the data being zero, there is a bit in there that is noise?
SERIN PORTA.4, N1200, [QUALIFIER,QUALIFIER],DATA1,DATA2
IF DATA1 + DATA2 = 0 THEN....

But if I have 2 bytes of qualifier that are working fine everywhere else in the program, why aren't they corrupt as well?

I'm a novice programmer....I'm also out to lunch on "timeout"
and was wondering if I'm missing something there.

Everything works great when it's wired.

I simply have the serout statement in the xmtr pic and the serin on the rcvr
and sometimes (but rarely) they can get out of sequence....I have led's on the xmtr and rcvr that should be in unison.

When they do get out of sequence, it usually just takes a second or so for everything to fall in line...so I never cared.

Am I doing something wrong here? I always wondered about the coordination between the two.