Re: X10 TM751 and "runaway" dims???

[nobody@xxxxxxxxxxxx (Dave Houston)]

4-5 years ago I conducted extensive tests using a Ming 310MHz RF transmitter
driven from the LPT port of a machine running W95 so I could control exactly
what RF was being transmitted.

I sent a single RF code and using a CM11A determined that the TM751 and
RR501 sent 3 contiguous dims to the powerline resulting in a 12% step. Three
contiguous dims (12%) take 550ms (66/120) to transmit as PLC. Each
additional dim takes 183.33ms (22/120). (If a PLC signal follows a previous
dim/bright by no more than 5 idle half cycles it will res.ult in an
additional 6% change.)

Starting at the end of the 105ms RF code I sent a continuous 1kHz modulated
310MHz RF signal for ~1000ms, varying the duty cycle until I found a burst
width that would cause more dims to be sent to the powerline. For the TM751
this was 60% (~600µs on, 400s off). I then reduced the duration of the 1kHz
signal until I found the point where one extra dim was triggered. This was
at ~535ms after the start of the RF code or about 430ms after the 40ms gap.
Another dim was triggered at ~735ms and ~935ms after the start of the RF
code. These timings were very repeatable.

With the RR501 a 40% duty cycle (400µs on, 600µs off) present ~200-300ms
after the start of the RF code would trigger an additional dim. The trigger
point was nowhere near as repeatable as with the TM751. What is notable is
that any device sending 5 copies of the RF code (e.g. HR12A) would trigger
an extra dim.

I did not check to see just when the PLC code started in relation to the
start of the RF code. The CM15A waits until near the end of the 40ms gap
before it starts sending PLC but I do not know about the TM751 or RR501.
Also, I incremented the duty cycle of the 1kHz modulation in 100µs steps.
The TM751 did not respond to a 50% duty cycle but did to 60%. I did not try
to refine it beyond that.

What this means is that if the data out line of the RF receiver section of
the TM751 or RR501 is high for sufficient time at certain points after an
initial RF dim signal an extra dim will be sent.

The RF section uses a data slicer circuit. The demodulated RF data envelope
is applied to one input of a comparator with the other input having a
capacitor that charges to 1/2 the average amplitude of the signal. When the
signal is greater than the charge on the capacitor the comparator output is
high, otherwise it is low. In the absence of an RF signal the TM751 RF
receiver section outputs continuous noise pulses. Most are of short duration
with an occasional longer one. It may be that inductive coupling of the PLC
signal can result in longer noise pulses. I did not try putting a scope on
the data out line to see what was present during an endless dim episode.