CMP 20 Eratic

[LarryNCarolynShirk]

This concerns the information panel (CMP) above the dining table in my coach.  When I tap any of the 4 micro switches, sometimes the reading for that position shows.  Mostly no change happens.  I took the panel off and found when I hold the box attached to the panel in my hand, all micro switches function perfectly.  When I pull out the panel just far enough to touch the metal box with one finger, it works.  When I let go of the metal box, the micro switches do not function.  Is this some kind of capacitance voodoo?  What is the solution?

Unplugging and reconnecting the unit had no effect.

Thank you for any ideas.  

Larry

[Edward Buker]

It does act like a capacitance switch and for some reason the sensitivity has changed. You are changing the signal to noise of your capacitance signal at the touch site by coupling your body to the metal frame of the unit. You could try and ground the metal box to the 12v coach ground, if it is not already, and then see if it works. If there is a ground wire attached already to the metal box frame you could disconnect it as long as there is a 12v ground to the circuit board still attached and the panel is still electrically functional. Basically tou are seeing if a change to the grounding of the frame makes a difference.

If you do not have success trying to improve the sensitivity with ground changes then as a last resort I would mount a metal screw through the panel or cabinet front and use a lug to attach a wire to the screw and then connect the other end to the metal box. You now have a path by touching the capacitance switch with one hand and touching the screw head with the other to enable touch functioning in the same manner as you have found works in your experiment.

Later Ed

[LarryNCarolynShirk]

Thank you Ed.  Somehow I thought you may have an idea.  That will be my project for tomorrow.  There are about 50 wires in that area.  One of them must be a ground.

Larry

[Edward Buker]

Larry,

I do not think the panel touch pads are the problem, I think the circuit attached to them has aged and changed. It is possible that there is a pot adjustment in the circuit, as a level set, but not likely and we do not have a schematic to sort that out.

Before you drill any holes for a screw, if it comes to that, put a short length of wire on a screw and attach the other end of the wire to the metal box and be sure that you get the same touch affect via the wire remotely as you do when you touch the panel directly.....you should but it is a bit of voodoo. That will save you an extra hole if it does not work. I also noticed my panel has some black wood mounting screws already. You may be able to wrap a small wire around one of those on the back of the panel and lead it up to the metal box and have no change in appearance. Good luck, hope it works Larry.

Now I was going to come up with an answer about having you make an outfit like the "Tin Man" and then touch the panel while standing on a metal stool but I was able to get the lighter side of me under control in time...:-)


Later Ed

[LarryNCarolynShirk]

Ed,

This morning at 50 degrees, the CMP-20 worked well.  So it must be capacitance related as well as temperature related.  At your suggestion, I added a wire from the metal box to the back of an external mounting screw.  Because it is not malfunctioning, I will try the screw touch next time an event occurs.  Sorry I could not find a metal stool on which to stand for the test.  

Larry