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Help with pager scanner
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Help with pager scanner

by storm on Thu Aug 26, 2010 10:56 pm

Hi all,

I'm following the instructions at http://www.adafruit.com/blog/2009/05/12 ... r-scanner/ and have hit a bit of a roadblock...

I get about 0.5v FSK output from the pager (looking at it with an oscilloscope), but the voltage pretty much dies (0.05v or less) once it goes through the NPN transistor. The video says that any NPN will do, this is the one I have http://www.radioshack.com/product/index ... Id=2062608

Do you guys have any suggestions on what I can do to fix this? Also, in the video there is a capacitor on the breadboard, but it's not in the diagram. Is it necessary? Thanks

EDIT: The output from the breadboard is up to 0.5v now, I must have had a bad reading. However, I still can't seem to get PDW to decode anything. I can see the FSK data flowing across the serial line, but the program isn't recognizing anything, whether it's configured with Slicer or RS232 and any of the options within each interface.
storm
 
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Re: Help with pager scanner

by JohnDowdell on Mon Aug 30, 2010 10:10 am

I suspect an MPS2222 will do just fine.
The capacitor appears to be there just to keep the supply from the RTS line stable. I'd choose 10uf, 16uf or 22uf @ 25v. Maybe it'd help, maybe it won't. You're pretty sure you're in an area that would receive these messages?

You say you are seeing good looking signal at the CTS line into the serial? You've observed this on an o-scope?

I havn't played with PDW before. Some of these decoders have options for signal polarity. Is there one? If so have you played with that? Had a look at the manual pdf but cant see it as an option. I guess if you're using the same paging receiver as the example then you probably don't need to worry about it.

Ladyada makes the point that the signal has to be bit bash decoded. She also makes the point that because of this a usb-serial dongle/cable will not work.

Check the advanced properties of the serial port. some serial ports have an auto-CTS option that should be unticked.
What version of windows are you using? serial ports got a bit funny after 2000.
Hardware handshake signal problems could be the version of windows, serial driver, serial port hardware or how the software programmer has implemented the serial. As a last resort you could try changing one of these at a time.

It could also be a timing issue. The software has to time the bits coming in. Somehow the software has to guage the speed of your PC in order to decode the bits. It may be possible that if other processes interrupt this routine when it happens, the timing could get thrown off.

There's some other (mostly dos based) decoders that you could also use to diagnose the problem if you're pretty sure the data into the serial port is ok.

http://homepages.ihug.co.nz/~Sbarnes/pocsag/software.html

JD
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Please be positive and constructive with your questions and comments.