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[jclarkw]

I want to eliminate RF interference between my new CM15A Computer Interface/Controller and my previously installed TM751 Transceiver.  (The range of the CM15A receiver is too limited, as others have found, so I need to keep the TM751 in order to use my HR12A Remote.)  X10 Tech Support referred me to http://forums.x10.com/index.php?topic=10807.msg61565#msg61565.  When I opened the CM15A box, I saw not one but two piggy-back "daughter" boards soldered into the main controller board.  The one connected to the external antenna is presumably the receiver.  The other, connected to another antenna wire inside the box, is presumably a transmitter that can be used with advanced ActiveHome Pro plugins to control other RF devices.  In addition to cutting the +V input wire to the former (receiver) daughter board, is there any downside to cutting the same wire to the latter (transmitter) daughter board? -- jclarkw

[Brian H]

If you still want to use RF commands to trigger thing in the CM15A but not to have it transceive RF back to the power lines.
In the Tools tab. Hardware configuration. Try checking the Transceived House Codes to NONE.

You may want to do some searching here. As there are a few users that have disabled the RF receiver of the CM15A.

If it still uses the same RF receiver board, as my older date code CM15As. The chip on it has a disable logic input pin. Has to be pulled high but can be done. I did one as an experiment.

There is some information on the CM15A on Dave Houston's web site and the FCC Database has CM15A photos, parts lists and schematics.
http://www.davehouston.net/cm15a.htm
http://transition.fcc.gov/oet/ea/fccid/
Grantee B4S
Product Code CM15A.

[Brian H]

One more point.
The schematic on Dave Houston's site shows four added bypass caps on the logic chips and power supply filters.
Many find it makes the CM15A much more stable.

[jclarkw]

If you still want to use RF commands to trigger thing in the CM15A but not to have it transceive RF back to the power lines...

You may want to do some searching here. As there are a few users that have disabled the RF receiver of the CM15A.

No, I want to eliminate the RF entirely, since I have no use for it and it appears to cause serious interference, especially with the activity log in ActiveHome Pro.

After studying the thread quoted in my first post, I have performed the surgery indicated there.  It has indeed eliminated the interference problem, but I have noticed other changes that logically should not be related:  The activity log in ActiveHome Pro no longer distinguishes between direct commands from ActiveHome Pro and macro-initiated commands; it now indicates all non-received events as "Transmit."  Also the activity log has become even more unreliable than before the surgery (see also my post at http://forums.x10.com/index.php?topic=27918.0.

[jclarkw]

The schematic on Dave Houston's site shows four added bypass caps on the logic chips and power supply filters.
Many find it makes the CM15A much more stable.

Yes, I saw that, but it's a much taller order than simply cutting wires.  Maybe I'll try it in the future...

[Brian H]

Well I did a few tests with my modified CM15A where I can switch the RF Receiver ICs enable pin high and low to disable or enable the receiver.
With the receiver enabled there is a constant static signal. Like a unsquelched two way radio. To the controller IC RF Received Input Pin.
When the receiver is disable but still has +5 power. The signal to the controller RF Received Pin is High.
Memory here as I didn't unpack the scope. When receiving an RF signal the data pulses low and then when done. Goes back to random static pulses.

My thoughts are. With the +5 volts removed. The controller IC is seeing a constant low and trying to decode data that should be there.
I tried a small test. With the RF disabled and a power line signal was received. The Activity Monitor showed a receive entry not an RF receive entry.

[jclarkw]

...When the receiver is disable but still has +5 power. The signal to the controller RF Received Pin is High...
My thoughts are. With the +5 volts removed. The controller IC is seeing a constant low and trying to decode data that should be there...

OK, so it sounds as though I had better disable the receiver (or tie the "controller RF Received" pin high -- is that easier or harder to do?) rather than removing power.  As I recall, you had specified what pin was used to disable the receiver, but I'm not sure if it would be the same in the latest batch of resurrected CM15A's.  Do you have any advice here?

Also, have you any thoughts on the effects of removing power from the transmitter?  I guess that should be benign, since one would expect no hand-shaking with the controller... -- jclarkw

[Brian H]

What is the silk screened part number on the receiver board?
Is the IC on the receiver board a RX3310?
The FCC Schematic shows a 20 pin RX3310 IC though my PCB uses a 18 pin IC.
Pin 9 is the Disable Pin with both 20 and 18 pin style ICs.

[jclarkw]

Well I did a few tests with my modified CM15A where I can switch the RF Receiver ICs enable pin high and low to disable or enable the receiver...

Brian H. -- Looking back at your old post, http://forums.x10.com/index.php?topic=10807.msg61640#msg61640, I see that you explain the procedure as follows:

"The receiver boards IC RX3310A has a Disable Pin on it.
There is some confusion between the Schematic on the FCC web site and the one in my CM15A. The schematic shows a 20 pin IC and mine has the 18 pin version.
Anyway pulling the disable Pin High through a 100K resistor; for safety to the chip; to the  +5 volts  disables it. Pin 9 of both the 18 pin and 20 pin ICs is the disable pin and it has a very small pad with a unused solder hole on it."

I'm confused:  Is it the RF receiver (daughter board) or the controller IC (18 or 20 pin DIP) that has the disable pin?  The schematic that I found on davehouston.org shows all but pin 10 of the 18-pin DIP connected to something already.  The receiver board is shown as having only 4 pins, all of which are connected.  The latter pins are labeled Vss, RF Out, Vcc, and RFin (whatever that means), none of which is shown as connected to an external antenna.  None of the pins on either the daughter board or IC is labeled "Disable" or anything like that.

I had cut the lead on **each** daughter board in my CM15A that was labeled +V.  I haven't re-opened my box yet -- waiting for more guidance... -- jclarkw

[jclarkw]

What is the silk screened part number on the receiver board?...

Sorry.  You sent this while I was typing.  I will open the box again and try to answer your questions...

[Brian H]

The RF Receiver Daughter Card is the one I was referring to.
All three schematic are on the FCC Database web site.
Dave has the Main Controller Board schematic on his site. The FCC has all three.
There is no Disable Label on the Receiver Daughter Card just an unlabeled pad and it does not connect to the main board.
Another way would be remove the RF Receiver Daughter card and just solder a 10K resistor from the +5 VCC Pad to the Received Data Out Pad on the main board.

[dhouston]

Well I did a few tests with my modified CM15A where I can switch the RF Receiver ICs enable pin high and low to disable or enable the receiver.
With the receiver enabled there is a constant static signal. Like a unsquelched two way radio. To the controller IC RF Received Input Pin.
When the receiver is disable but still has +5 power. The signal to the controller RF Received Pin is High.
Memory here as I didn't unpack the scope. When receiving an RF signal the data pulses low and then when done. Goes back to random static pulses.

My thoughts are. With the +5 volts removed. The controller IC is seeing a constant low and trying to decode data that should be there.
I tried a small test. With the RF disabled and a power line signal was received. The Activity Monitor showed a receive entry not an RF receive entry.

The data output pin will always have continuous short noise pulses - that's the nature of the data slicer (i.e. the comparator circuit shown in the receiver data sheet http://www.allparts.co.kr/pdffile/pdffile_001/3274.pdf). On a 'scope the input to the comparator will resemble the 'scope shots shown at http://davehouston.org/rf-noise.htm. It is extremely unlikely that the CM15A microcontroller responds to anything other than valid X10 RF signals at the output.

Adding the decoupling capacitors might improve things but I think the OP is chasing gremlins.

There can be PLC collisions caused by both receiving the RF and sending it as PLC but the CM15A should detect this, then back off and retransmit after the line is clear.

The best course of action would be remove power from the RX3310 receiver and rely on the TM751 or get rid of the TM751 and improve the CM15A reception as detailed here.

• http://davehouston.org/ImproveCM15A.htm

Range measured in hundreds of feet is possible.

A distributor is currently conducting range tests and looking into where to manufacture the antenna hardware for the CM15A. TM751A and RR501. Kits should be available soon. It could have been available earlier but a community organizer who agreed to conduct range tests accepted about $300 worth of my hardware and then stopped responding to my emails - live and learn. I've been totally disabled for the past 20 years and am unable to supply these myself beyond a few prototypes.

[Brian H]

Any idea what happens if the +5 to the receiver is removed and the output to the controller chip is sitting low and not randomly pulsing low?
When I tie the Disable pin of the RX3310 High the output to the controller is also a constant High.

[Noam]

I want to eliminate RF interference between my new CM15A Computer Interface/Controller and my previously installed TM751 Transceiver.  (The range of the CM15A receiver is too limited, as others have found, so I need to keep the TM751 in order to use my HR12A Remote.)  

I'm guessing that the "interference" to which you are referring is when both the TM751 and the CM15A receive the same RF signal, and both try to act on it.
Have you tried (as was suggested here) settings the "Transceived House Codes" to "NONE"? That *should* prevent the signal from being acted upon twice.
Another thing to try might be the CM15A "Antenna Reflector" mod. Simply put, you secure an 18.5-inch wire alongside the CM15A's antenna, WITHOUT an electrical connection between the two. I used two strips of masking tape the first time, and it worked great. The longer wire (I *think* it is a half-wavelength) helps bring in the signals, and "funnel" them toward the CM15A's antenna. I've used this mod on my own units for a few years, and it have improved RF reception greatly. You might be able to improve it enough to the point where you can eliminate the TM751. It is certainly worth a try.

[dhouston]

Any idea what happens if the +5 to the receiver is removed and the output to the controller chip is sitting low and not randomly pulsing low?
When I tie the Disable pin of the RX3310 High the output to the controller is also a constant High.

The microcontroller is going to ignore anything that does not begin with the X10 STX signal (9ms pulse/4.5ms space) or the similar but shorter start sequence from the camera remote. Then it will only act on valid codes that follow the STX sequence.

• http://davehouston.org/rf.htm
• http://davehouston.org/cr14a-rf.htm