Re: X-10 RF meter (was Re: XTB II Review)

[nobody@xxxxxxxxxxxx (Dave Houston)]

"Jeff Volp" <JeffVolp@xxxxxxx> wrote:

>"Marc_F_Hult" <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote in message
>news:ghfqp257tr59qhe472qjbdenvksr4tkouj@xxxxxxxxxx
>
>> So a one-off X-10 RF signal strength sniffer/meter could indeed be
>> constructed *without* programming for ~$15 or so (depending in part on
>what
>> is already in your electronic junk box).
>
>While I agree a DIY version without a custom PCB or case can be put together
>cheaply, I don't know of any electronic distributers that offer free
>shipping.  That can become a significant factor when buying from multiple
>sources.
>
>I had used a receiver some time ago that included an analog RSSI output
>(received signal strength indicator).  That was useful to determine how to
>dynamically configure the RF network for best performance.  The RSSI output
>could be monitored by a VOM.  However, because of the pulsed nature of X10
>signals, some type of filter or peak detector may still be needed.

Jeff,

Don't get misled. I've been using these receivers for several years, buying
the RWS-374-2 direct from Wenshing in Taiwan until they raised their price
beyond where it made sense. The Radiotronix receiver is made by another
Taiwan company.

     http://www.wenshing.com.tw/DATA/RF-MODULE/RWS-374-2.pdf

The Wenshing datasheet has always labeled the two outputs "linear" and
"digital". I see they have recently started silk-screening "RSSI", on the
module itself, for the "linear" output but this is misleading as it requires
further processing to use it as RSSI.

In the absence of a signal, there's a continuous noise output on both the
"linear" and "digital" pins so just measuring the voltage tells you nothing.
When I tried a VOM yesterday, there was a negligible difference between
signal and no signal which is why I then wrote that a PIC is needed.

A PIC is required to separate the wheat from the chaff. The PIC analyzes the
signal, validates it as an X-10 signal and then measures the difference
between the final pulse and space which is a good indicator for signal
strength. This is the way the BX24-AHT did it although it merely output the
ADC value rather than use it to drive an LED.

It will be necessary to spend an extra $0.25 on a PIC12F683 as opposed to a
PIC12F675. The PIC12F683, as you know, has hardware PWM which can be used to
synthesize an analog voltage proportional to the signal strength. You could
do this yourself in software but it would be discontinuous since you have to
take time to capture and analyze the signal.

The first screenshot on this page...

     http://davehouston.net/rf-noise.htm

shows you what the two outputs look like under signal and no signal
conditions.

http://davehouston.net
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