|
mjwalt Post subject: Signal received only when transmitter is probed
Unread postPosted: Fri Oct 15, 2004 7:40 pm I am using a Melexis
transmitter (72031 - 915 MHz, FSK) in a remote sensing device. The problem
I have encountered is that the receiver will not receive the signal
(so I assume the transmitter is not transmitting) unless a wire of some
sort is placed on the ROI pin of the transmitter. This wire need not
be grounded and has to be a couple inches long for the 'wire fix' to
work. I found this 'solution' while using the o-scope on that pin. My
only experience with RF comes from the LINX line of transmitters and
receivers so designing with a non-'Plug-n-Play' device is giving me
some problems. Could this be a ground loop problem or is it something
more complicated. Any advice would be greatly appreciated. Thank
you, Mike Walters Top Kirt Blattenberger
Post subject: Unread postPosted: Sat Oct 16, 2004 10:18 am
Offline Site Admin User avatar Joined: Sun Aug 03,
2003 2:02 pm Posts: 308 Location: Erie, PA Greetings Mike:
Without knowing what your baseline configuration is, it will be
difficult to provide much help. The wire on the ROI pin causing the
Tx to work could be due to many things from a bad solder joint to a
faulty crystal or other component. Even the IC could be damaged from
ESD. Could you please take a look at the couple questions below to provide
a little more insight into your situation to others and me? I
took a quick look around the Melexis website and found that they offer
a demo board for the TH72031. https://www.melexis.com/prodmain.asp_Q_c
... E_EVB72031 Is that what you are using for experimentation?
If not, does your PCB layout generally follow the outline given on page
8 of the user's guide that comes with it? https://www.melexis.com/prodfiles/evb72031-rev005.pdf
You have probably already seen these, but there is a page on the
Melexis website with application notes. https://www.melexis.com/apps.asp?offset=0
Here is the datasheet for the part if anyone else cares to offer
an opinion. https://www.melexis.com/prodfiles/th72031-rev005.pdf
What are you using for a receiver? If it is one of the Melexis devices,
are you using the recommended PCB layout for it? Finally, do
you have aspectrum analyzer available for troubleshooting?
Sincerely, Kirt Blattenberger :smt024 Top
Profile Guest Post subject: Unread postPosted: Tue Oct
19, 2004 2:35 pm For the transmitter I am using the circuit
shown on the Melexis data sheet for the EVB with the same values for
all components although the physical layout is quite different to fit
on my PCB. On the receiver side I am using the Melexis EVB (TH71111)
just to ensure the transmitter is operating properly. As far
as the spectrum analyzer goes, I don't access to one. Thanks
for the reply, Mike Top mjwalt Post subject:
Problem Resolved Unread postPosted: Wed Oct 20, 2004 3:36 pm
For anyone interested... The problem was indeed a simple
one. The 'wire fix' was simply adding a certain amount of capacitance
to the circuit and thus tuning the frequency to a value within the bandwidth
of the receiver. In the end, with a little trial and error, it took
changing a few capacitors to different values (quite different from
the data sheets) and now, all is well. Mike
Posted 11/12/2012
|