DAC / PWM Output Circuit
The digital output data from the microcontroller can be processed in either of two ways. The first
uses a serial data output on pin 12 (PB0) which is applied to the input of the serial input Quad
“digital to analog converter” or DAC IC U4 on pin 9 of that device. Analog output voltage from
three of the four DAC channels is output on pins 11, 12, and 15 of U4, and applied to the inputs of
the LED driver array. The second output method uses “pulse width modulation” or PWM data from
the processor on pins 13, 14, and 15 (PB1, 2, and 3) which are applied to the quad op amp IC U3 on
pins 12, 10, and 3, respectively. The filtered output from these op amps is then applied to the inputs
of the LED driver array. Only one of these two output methods is installed on the circuit board,
with the components for the alternative method omitted.
LED Array and Driver Circuit
The LED array is a separate circuit board from the microcontroller, and attaches to the CPU board
through the power and signal interface plugs P1, and P2. The LED display board is the simplest
portion of the circuit, as it consists of 3 identical circuits, each containing 16 LED elements, an op
amp, and a driver transistor. In each section, the LED emitters D1-D16, D17-32, and D33-48 are
wired as an 4 column by 4 row series-parallel array. Each array is connected to the 24 volt DC
supply, with the op amps U1 and U2, and the current regulating transistors Q1, 2, and 3 responding
to control voltages from the microcontroller to determine the current flow through each portion of
the array. Depending on the settings of the microcontroller, each of the three section may be
controlled independently ar will act as a single unit.
Service Access
The active electronics of the BL-48 illuminator are mounted on two circuit boards inside the main
housing of the unit. These may be accessed by removing the four screws along the sides of the unit
to open the main housing. The unit may be operated normally with the cover removed. Provided
that the unit is operated with a suitable power supply, there are no hazardous voltages present in the
interior of the unit
Basic Troubleshooting
With the exception of the microcontroller, the circuitry used in the illuminator is quite simple, and
troubleshooting is made quite easy by using the available power and data sync indicators and
manual operating modes, and by observing the LED array for any erroneous output.
In the event that the illuminator fails to produce a normal output, first check for good AC power to
the power pack, and for the LED power indicator on the rear panel. If the LED indicator is not
active, then the external power pack or supply is not powered or is defective.
If the power LED is lit, apply DMX data to the unit, and observe for illumination of the “Sync”
indicator adjacent to the Power indicator. If the Sync LED is lit, the unit is receiving normal DMX
data, and should respond to data within the proper address range. If the unit does not respond,
check the settings of the DMX address switches for correct settings.
