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=== Analog Theory of Operation===
=== Analog Theory of Operation===
Here is a simplified diagram of the Analog and high voltage part of the system:
Here is a simplified diagram of the Analog and high voltage part of the system:
[[Image:lighting_block2.png]]
[[Image:lighting_block.png]]


The high current switching element in an AC dimmer is an optically coupled
The high current switching element in an AC dimmer is an optically coupled
triac. These are commonly known as SSRs (Solid State Relays) SSRs will turn
triac. These are commonly known as SSRs (Solid State Relays.) SSRs will turn
on when a voltage is applied across the control pins. Once an SSR is turned on,
on when a voltage is applied across the control pins. Once an SSR is turned on,
it will not turn off until no current flows through it.
it will not turn off until no current flows through it.


AC dimmer circuits exploit this fact by turning the SSR on in phase with the
AC dimmer circuits exploit this fact by turning the SSR on in phase with the
AC waveform.  For example, to run a light at 25% intensity, you'd use a control
AC waveform.  For example, to run a light at 50% intensity, a circuit pulses
voltage of 1.6 volts. The comparator would not turn the triac on until 75%
the SSR about half way through each phase of the AC sine wave.
of each sine wave. The comparator would automatically turn the SSR off at
the end of the wave because the integrator would reset back to 4 volts.  A
voltage above 4.0 volts or below 0.8 volts hold the output always on or
always off.


 
See [[Lighintg Analog Details]] for the full description of the analog circuitry.
See [[Lightintg Analog Details]] for the full description of the analog circuitry.
Status: Implemented and working. A respin of the PCB to fix a routing error may be required.
 
The low pass filter on the input means that the lights can be controlled with
a PWM circuit instead of an analog voltage. A PWM circuit controlling the
lights should have a base freequency of between 2,000hz and 20,000hz for
the best results.  In the example above, you'd use a PWM circuit set at
36% duty cycle.  The input impedence is about 5K ohms.


==Computer Control System==
==Computer Control System==
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