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Building the RV Super Dimmer.


I call this a "Super" dimmer because after you understand the functionality of the dimmer, I think you will agree that there is no other dimmer that can match this one. So lets get right into what makes this dimmer unique:

  • Can dim most DC powered LED fixture, including Puck Lights, and LED Strip Lights.
  • Can be built as a High-Side, Low-Side, or Combo High-Low side dimmer.
  • Two independant momentary switch control inputs
  • Can be used with the Lippert Linc system or stand-alone.
  • Third optional input that can be used as an override, or sensor such as a photocell.
  • Opto-Isolated inputs.
  • Fused to protect dimmer and LEDs attached to it.
  • TVS Diode surge protection.
  • Logarithmic dimmer control.
  • One, Two, or Four hour turn off delay.
  • Microcontroller based - can change functionality as needed.
  • Low standby power (7mA)... less than lead acid battery self-discharge rate.
  • Field Programmable.
  • Status LEDs
  • Can handle 40Watts of LEDs.

I think you will agree that after considering all of the features of this dimmer, you will not find another one on the market like this... it is truly the "Superman" of LED Dimmers!



While this dimmer will work with some LED fixtures having Switch-Mode drivers, due to their many different performance characteristics, I do not recommend dimming these lights.




High-Side and Low-Side Dimmers

High-Side vs. Low-Side dimmers. When selecting a commercial dimmer, they will be either a high-side or low-side dimmer. The criteria for determining which dimmer to use is... cost. High-side dimmers are slightly more costly and a bit more difficult to design than low-side dimmers. For the RV Super Dimmer, you can build either a high-side or low-side dimmer... the choice is yours.

The difference is shown above. Simply put, the "side" is where the dimmer control is. For a high-side dimmer, the dimmer is "higher" or "above" the load (LED) when connected to the 12V power supply. Conversely, a low-side dimmer places the dimmer control "below" or "lower" than the LED, essentially connecting it to Ground.


Low Side Dimmer Problem

Since the Dimmer is referenced to ground in a Low Side dimmer, a problem exists when attempting to connect a LED to the dimmer that is also referenced to ground. This is an incompatible situation, and the LED will either never turn on, or it will never dim or turn off. This situation also exists when a LED is not grounded, but the negative path back to the distribution panel is not accessible. In these situations, you must use a High-Side dimmer.


High Side Dimmer

If we use a High-Side dimmer to connect a ground referenced LED, then everything works. In fact, the High-Side will work with any LED light fixture or LED strip, grounded or not. And it is for this reason I am showing the High-Side dimmer.


Linear vs. Logarithmic dimming

Even something as simple as how the dimmer control works has been considered in this dimmer. The blue line in each chart shows the dimming control, and you can see that the left side, the control is linear; that is - the change rate is constant over the entire rotation of the control.

Unfortunately, our eyes do not see light intensity in a linear fashon. This is represented by the red line. On the left, notice that when increasing voltage from zero, there is an initial rapid increase in intensity. And the intensity has reached around 90% of it's full value after only 40% of voltage increase. The remaining voltage increase does not significantly change the intensity (or at least our eye's perception of it).

However, if we make the control logarithmic as shown by the blue line on the right chart; that is - the voltage rate of change is not constant; then our eyes percieve the rotation of the control to be linear. This function is done in the MicroController simply by using logarithmic math. This is the beauty (and advantage) of software control - we can change the rate of change simply by changing a mathematic equation.

This function is done in a single line in the sketch (firmware). As well, a linear version is disabled, which makes it easy to try both versions and compare their effect. Logarithmic potentiometers do exist (but on-board log trimmers are expensive), however, you are limited to one of three or four popular "tapers". By manipulating software, you can infinitly tailor the logarithmic taper, and could even customize it for a particular model LED fixture.


Block Diagram

The block diagram for the Super Dimmer shows that the two inputs are connected to the opto-isolator via isolation (steering) diodes. There is also a TVS surge suppression diode here. The opto-isolator provides electrical isolation for the MicroController from the outside world, as well as level shifting (the opto-isolator operates at 5VDC). The opto-isolated input to the MicroController is TTL (Transistor-Transistor Logic).

The MicroController also receives input from a potentiometer attached to it's internal 10Bit Analog-to-Digital Converter (ADC), which provides a digital number (0-1023) relative to the voltage (0-5V) on the potentiometer. This allows the MicroController to set the duty cycle of it's Pulse-Width Modulated (PWM) output to the MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor) to reflect the position of the potentiometer.

Simply put, when the potentiometer is at minimum voltage, the ADC output will be 0, and the PWM duty cycle will be 1%. When the potentiometer is at maximum voltage, the ADC output will be 1023, and the PWM duty cycle will be 99%. We get dimming by varying the PWM duty cycle.

There is also a power supply on-board to provide 5VDC to the MicroController. The Input Override and Timer Delay switch simply places a ground on the MicroController to instruct the MicroController to perform those functions.

Up to this point, all of the components and functionality of the High-Side and Low-Side dimmers are identical. However, the logic that drives the MOSFET is inverted between the High-Side to Low-Side versions.

This requires a logic inverter (High-Side only), performed by the 2N3904 Transistor. It also requires a different MOSFET. The High-Side version uses a P-Channel MOSFET while the Low Side version uses a N-Channel MOSFET. The more expensive P-Channel MOSFET and additional logic inversion transistor is why the High-Side dimmer is more complex and (slightly) expensive to build.





Dimmer Functions (High Side dimmer shown).


The Dimmer is constructed in a "potted" (encapsulated epoxy) chassis mount, which provides access to all of the functions, and provides reasonable protection. The dimmer is designed to operate with a minimum amount of connections, but also provides a flexibility for a wide range of applications.


Minimum Dimmer - Linc Receiver.


The dimmer is a High-Side dimmer, which allows the LED to have a grounded negative, or a floating negative (note that the Dimmer negative lead is for it's own operation - not for the LED). In this configuration, a motor/relay channel from the Lippert Linc Multi-function receiver is attached directly to one of the two inputs.


Minimum Dimmer - Stand Alone.


In the minimum stand-alone configuration, a pushbutton is all that is required. Note though that external power must be connected to the pushbutton as well as a ground on the input. This is required to replicate the Linc receiver (as the receiver itself provides 12V and Gnd).

In this scenario, the Function Channel output ia a momentary "ON" switch. The latch will convert that ON command to alternate between ON and OFF, in much the same way the Receiver's built-in LIGHT channel operates. Therefore, subsequent operations of the remote light switch will alternate turning the light switch ON and OFF.



As stated, there is a wide variety of connection capability with the dimmer, including but not limited to any combination of:

  • Lippert Linc Receiver relay output on Channel 1 and/or cChannel 2.
  • Momentary pushbutton on Channel 1 and/or Channel 2.
  • 315Mhz/433Mhz RF Wireless Relay Remote Control on Channel 1 and/or Channel 2.
  • Internal (dimmer based) or external dimmer control via 10K Ohm potentiometer.
  • SPST override switch on Aux Input.
  • Photocell on Aux Input (requires Photocell module and software change).


Optional Connections.


Any combination of inputs can be attached to the dimmer as shown above. However, care must be taken to ensure proper connection as each input varies. See the Dimmer schematic for details.

For example, when connecting the Lippert Linc Receiver to an input, external 12V and GND does not have to be supplied as the Linc Receiver provides those signals.

For the momentary pushbutton or RF Wireless Relay Remote Control, 12V and GND must be supplied to drive the Opto-Isolator on the Dimmer board.

For the Aux Remote - power is provided by the Dimmer for either switch or Photocell. As most photocell boards output a proportional voltage, it must be opto-isolated from the Dimmer. Currently this board is not in production... if there is enough interest, one will be designed.


Pin Assignment.


Connection pin assignments are shown above. Refer to the dimmer schematic for more details.










Last reviewed and/or updated Feb 28, 2017