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18. Temperature & Motor Control Module R764203
An 8-bit micro-controller P87LPC768P is slaved to the CPU via an SDAI and SCLI bus. In the event of a cooling problem with heavy
risk of damaging the DMD's, an IRQ_DMD line informs directly the CPU to shut down the projector.
Some data are programmable, like start and stop conditions of the DMD cooling, and this data is programmed via the micro-controller
into the E²PROM I402 using its own local I²C bus SCL0/SDA0.
The temperature of each DMD is measured with an NTC resistor and the analog informations NTC1/2/3 are converted into a digital
value in the controller. The result is compared in a LUT (Look Up Table) with a pre-installed and programmed value. The Pelletier
elements are switched on from some threshold level onwards and switch off again as soon a working temperature is obtained.
The DMD's are also permanently cooled by fans running at a constant speed (J12, J15, J18).
As the micro-controller does not have sufficient I/O pins, an 8-bit addressable latch 74HC259 (IC401) is used. As the RESET or
CLEAR pin is permanently high level, the IC only can work in the "Memory" and "Addressable Latch" modes. Three address bits
A0/A1/A2 select one of the eight latches and the DATA IN information is then transferred to the addresses latch in the "addressable
latch" mode when the ENABLE_259 is low.
Three latched TEC1/2 and /3 outputs turn Q100, Q101 and Q103 on when needed. A yellow LED visualizes the active status of the
cooling element. The amplitude of the +TEC voltage is programmed on the SMPS board where this voltage is generated.
Three other outputs MUX0/MUX1/MUX2 are used for the 1 of 8 data multiplexers I104, I105 and I107.
Multiplexers I104 and I105 are an extension of the micro-controller. The encoder data of the zoom and focus motors are taken in by
the controller via the Schmitt trigger-inverter I103 and the multiplexers I104/I105.
PRISM protection
The projection lens might be turned in by the zoom motor so far that the lens body could touch the DMD prism. Lens or Prism can
be then be damaged. A sensor, connected to J20, detects this extreme position of the lens and the micro-controller stops the motor
and even reverses the rotation to push it a little back, away from the prism.
Note that there is room for more encoder motors, but CHA2/CHB2 and CHA3/CHB3 are not used (see bloc schematics).
Motor Drive - Control
There is a common circuit for generation of the required motor current PWR_DRV. The current flows through Q204/Q205 as long
Q202 remains blocked.
This circuit is initialized at power start up by C200/R201/Q200/Q201. These transistors are switched on a short time until C200 has
charged up.
The RST_LOG is passing a Schmitt trigger-inverter of I102 and enables the de-multiplexer I107.
The power circuit of each motor is identical. A series transistor in the power rail is turned on to supply a dual power OPAMP L2726.
A voltage, fixed by R215/R218, installs a level at the "+" or the" -" input. The FWD and REV lines allow thereby a current flow in the
motors in two directions.
Overload:
The motor current is flowing in R203/R204 and in the event of an overload, the voltage drop across these resistors reaches the
0.5V threshold and Q202 turns on. The collector current of Q202 charges C203, Q205 gets opposite biased due to the voltage drop
across R210 and finally Q203 turns on.
The OVL line goes low, but this line is not used (anymore) as the micro-controller always gives a "Reset Overload" by pulling low
the OVL_RST line, prior to start a motor (even when there is no overload). The OVL_RST line is a latched output of I401.
Shutter2
The SHUTTER2 motor is related to the Contrast Enhancement in the menu. A mechanical shutter (Iris) is inserted in the relay optics
between the integrator rod and the folding mirror to improve the contrast. However, the light output decreases as a consequence.
DMD Temperature Control
A TEC (Thermo-Electric Cooler) is a solid state heat pump that utilises the Peltier effect. During operation, a DC current flows
through it, causing heat to be transferred from one side of the TEC to the other, creating a cold and a hot side.
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R5976820 SLM R12+ PERFORMER 08/03/2005
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