Until recently pretty much all the ceilings in my house including the hallways were popcorn ceilings.
This was popular in the 60's and 70's as a cost saving measure because the popcorn hid the minor defects
that would be too obvious if regular paint was used. In fact when I bought this house in 1989 most of
the popcorn was also covered in glitter, something that went out of style even more quickly than the
plain popcorn. In 1989 I hired a painter to spray all the ceilings (except for one room) with white
paint. So although the popcorn look still remained at least the dreadful glitter was gone. The popcorn
including the one room with glitter remained until January 2026 when I hired a contractor to cover up
all the ceilings with grooved paneling, using 1x6 molding strips to hide the seams and to give depth to the design.
As part of this project, I also added modern recessed lighting.
I used the 4 inch lights shown on the left (purchased
here
in the bedrooms and hallways. These lights look elegant and are surprisingly bright for their size. The 4 inch
lights would be fine for the rest of the house as well but I like very bright lighting so for the kitchen,
family room and living room areas I chose the 6 inch lights shown on the right (purchased
here).
These 0-10V dimmabble lights are also available in 8, 10, and 12 inch sizes but I didn't use them.
Most lights require only 3 wires to be hooked up to provide the 120VAC power in the US. (In many other
countries 240AC power is used.) These wires are usually called hot, neutral, and ground. The hot and neutral
wires provide the power and the ground connection provides additional safety for certain types of electrical
failures. In older houses built before the 3rd wire grounds became part of the electrical code (like my house),
only the hot and neutral wires need to be hooked up. If you wanted to dim the lights you would buy a dimmer switch
that would modulate the AC power to reduce the power going to the lights when you don't want the full brightness.
These lights are different however. If you want to dim them you need two additional wires routed from the
lights to the dimmer switch. The dimmer switch does not modulate the AC power like most traditional dimmer
switches but instead simply provides a 0-10V signal to the lights to control the brightness. (10V commands
full brightness.) It can be a pain to run these two extra wires, but still these lights have become at least
somewhat popular because it's a smoother and more efficient way to control the brightness and is never subject
to flicker. (Flicker can be a problem with traditional dimmers and can be dramatically bad if the wrong
dimmer is chosen for the type of lighting used.)
The dimmer switch I used (at least at first) is shown here and was purchased
here.
Note that this dimmer can't be used with the traditional 3 wire lights. It can only be used with the lights
shown above or similar ones that advertise "0-10V dimming". I hooked up the dimmer wires from all four
lights in the room to the dimmer switch as per the instructions. The dimmer worked, but I wasn't
happy with the performance. When I moved the dimmer slider from the top to the middle of the range the lights
dimmed by a barely noticeable amount. Even when I moved the slider down more to the 1/4 position the dimming
amount was still quite small. So most of the control, from close to full brightness to
off happened during the bottom 1/4 of the slider travel nearly wasting the top 3/4 of the travel range.
This makes it touchy to adjust the brightness to the desired level. That was the defect that inspired me
to design my own dimmer.
To explain the source of this defect, I'll digress slightly to discuss potentiometer tapers and our hearing
and sight sensing capabilities. Our ears can detect sounds over 12 orders of magnitude from the threshold of
hearing at 1 pico-watt/m2 to the threshold of pain at 1 watt/m2. To sense such a huge
range of sound levels, our hearing sense almost has to be logarithmic. This means we can sense smaller
changes in sound power when listening to quieter sounds than for louder sounds. To create a percieved doubling
of the sound level we need to more than double the sound power exposed to our ears. (Typically we need to
increase the sound level by a factor of 8 to 10 to get this percieved sense of twice as loud.)
If we plot the resistance of a typical potentiometer as a function of the knob angular position we get a
plot such the one on the left. This is called a linear taper potentiometer.
(It won't be this perfect, but this is the ideal.) It would not be ideal to use such a potentiometer to
control the sound power to a speaker. The first half of the rotation would increase the sound level from zero up to
pretty much the maximum because we don't hear much difference between max power and max/2. This means we are essentially
waisting the 2nd half of the rotation. In most circuits, the potentiometer controls amplitude instead of power.
Since power is proportional to the square of the amplitude, the control is improved somewhat but we can still get
better control of the volume by using a different taper. Instead of a the linear resistance curve the resistance should
increase exponentially.
As an example, let's look at the percent resistance vs. position of a slider potentiometer that I will later
be using with my custom dimmer. It's spec sheet shows the chart on the right of resistance vs. position.
Although it has nearly straight segments (which is common as it is probably easier to build) if you smooth that
out in your mind it does look like it approximates an exponential curve. This is often called a log taper which
is paradoxical because the transfer curve is the inverse of that. It gets that name because it is used to counter
the logarithmic nature of our hearing. The term "audio taper" is also common which I think is better because it
is not ambiguous or paradoxical. If you hook it up backwards, then the transfer curve is actually logarithmic
and I've heard this refered to as exponential or reverse logarithmic both of which are paradoxical. (Perhaps
reverse audio would be better.) The specific transfer curve shown in this chart is sometimes referred to as a 15% audio
taper because the resistance is 15% of the maximum at the center position. (Values between 10 and 20% are the most common.)
Our eyes can instantaniously see light over a dynamic range of about 5 orders of magnitude and if given some
time to adapt to low light levels we can see an additional 5 to 8 orders of magnitude beyond that. This suggest that
when adjusting light intensity an audio taper would be appropriate for the same reason it is useful for sound intensity.
It was surprising and annoying then that the dimmer switch I mentioned above did not use an audio taper. It appeared to
be nearly linear and probably even curved somewhat in the wrong direction (i.e. reverse audio). Of course my own dimmer
design would not suffer from that problem. It also occurred to me that it wouldn't be that much harder to put in a
separate potentiometer for each light in the room rather than the traditional approach of controlling all the lights
in the room with a single control. I did this partly because I thought it was cool. I did think it would be occationally
useful as well, and once these dimmers were installed I was surprised how often I adjusted the lights individually.
Here is a schematic of my six position dimmer which I installed in my family room and master bedroom.
(The schematic for the four and two position dimmers is the same with some of the lights and sliders removed.)
The red lines represent the connections for the individual positive terminals of the 0-10V dimming signal and the black lines
represent the negative terminals (common).
I will now discuss the parts used starting at the top of the diagram and working our way down.
Since I have already discussed the lights, I'll start with the switch shown at the top right of the schematic.
I bought the switches shown on the left because they were inexpensive and I liked the style and the fact
that they are illuminated when the switch is off. Amazon also sells a single pole version (about 10% cheaper)
as well as a single switch (for $9.69) if you don't need the 10 pack. This inexpensive switches worked well
for the rooms with 4 or 6 lights (a total of 60 to 120 watts). But in the kitchen and hallways, with just
2 of the four inch lights (a total of 30 watts), these switches did not work well. They are still safe and
effective in turning the lights on and off, however the switch illumination flickers. I believe this is because
the switch was designed to be used with higher wattage lights. The flickering is not dangerous, but it is
annoying, so in this low wattage situation I used the switch shown on the right. No flickering with those, the
only drawback is that this switch is more expensive. The 120VAC power is connected to the lights and the switch
using standard electrical practice appropriate for the electrical code in your area. (These lights and switches
are also compatible with 240VAC and so no changes to this dimmer circuit are required if you live in a country
that uses 240VAC house wiring.)
The six 12 foot cables coming from the (pink and purple) light dimming wires use this cable shown
on the left. The picture on the right shows the 10 foot cable attached to one of the junction boxes
that comes with each light. (The aluminum conduit going off the left side of the picture is attached
to the lamp.) The black and white wires are connected to AC power with the two orange lug nuts, but
this was just temporary to test out the lamp and dimmer circuit. Of course when installed the white
and black wires would be feed thru a metal bushing inserted into one of the junction box openings.
Although I used the black cable shown on the right for later builds, this was the first one I built
and I used the white wire shown here which I happen to have laying around. The green wire normally
goes to the third wire ground but my home is older and was not built with a third wire ground
(except for a few circuits in the kitchen). So I just bundled up the green wire along with the pink
and purple dimming wires to keep it out of the way.
As you would expect, I used the red wire of the 2 conductor cable as well as the red wire of the JST
connectors (pictured below) for the positive 10V signal and the black wires for the ground (common).
You might guess that the pink dimmer wire (which looks somewhat close to red) from the lamp should
be connected to the red wire. But NO! The pink wire is actually the negative and so you should connect
it to the black wire of the cable and the purple wire is the positive and should be connected to the
red wire of the cable. (As you can see later, all the negative wires are connected together). If you
reversed the pink and purple, the purple wires would e connected together and the dimmer circuit would
not work. (In my opinion this was a poor choice of colors by the lamp manufacturer.)
As you can see from the picture on the right, the female JST connector is connected to the other end of
the 12 foot 2 conductor cable coming from the light. During installation, all six of these female JST
connectors will be gathered together near the light closest to the on/off switch where they will be
connected to the male JST connectors attached to the 7 wire cable shown below. Allthough my diagram calls
for all six of the 2 conductor cables to be 12 feet long I didn't actually build it that way. For a very
large room a few of the cables might need to be even longer. Also the lamp closest to the switch doesn't
really need a cable at all and the female JST connector could be connected directly to the pink and purple lamp
dimming wires.
Next it's time to build the ten foot 7 conductor cable. On one side of the cable I attached 6 male JST connectors.
The colored electrical tape just below each JST connector (on the picture to the right) are not covering up
any electrical connection. The tape is just there to identify the six different lamps. On the other side of the
ten foot cable I attached one of the IDC connectors shown below. I cut one of the cables in this set in half
and used one end or the other, split the 8 wires apart on the ribbon cable, stripped the insulation and soldered
it to the 7 conductors of the 10 foot cable and protected all the connections with shrink tubing. The first time
I built this cable I attached the 8 pin ribbon cable before installation. However it was too difficult to thread
the cable from the attach down to the switch box so I ended up cutton of the ribbon cable part, then twisted the
7 wires together to create the smallest footprint possible to snake the cable from the attic down to the switch box.
Once the cable was sticking thru the switch box, I reattached (soldered) the ribbon cable and again protected
it with shrink tubing.
note: More to follow ... I'm still working on finishing this page
1.5K resistor.png
JST Connector
Ribbon Connector
2 Conductor Cable
7 Conductor Cable