SteveW said:
I need to use the range of the single DAQ output, to be able to code the
brightness from 0 to maximum intensity, of each LED independently. I'll
use Labview to provide a control voltage, to be the source of the
designed circuit. This voltage value, needs to encode a 'brightness
level' for every single LED, so that any combination of 0 to max of each
LED individually may be continously set.
I'm not very competent at electronic design, so thought I would ask you
guys first to point me in the correct directions for further research
I need the LED's to be very bright, so they will need to be driven by a
high power source. The trick is to have each LED's brightness to be
accurately controlled and the same dynamic range. Basically, I need a
controlable 8 LED 'display monitor' with the ability for very high
luminosity in a continous time domain - all set by a single voltage
source.
Sorry, did I do better explaining that time?
thanks for the interest, regards Steve
Steve,
the problem, as I understand it, is to encode 8 independent
analog values within one analog value. Leaving the issue of
resolution and bandwidth aside for the moment, you have a
few basic options:
a) Drop the requirement to use a single, Labview driven DAC
output. Use any digital I/O port (RS232,Parallel,USB) to talk
to a PWM chip or a microcontroller. Personally, I would use
a programmable logic IC (e.g. Coolrunner) to implement an 8
channel PWM and interface it to serial, parallel or USB ports.
b) Go digital. If it's got to be your analog channel, just drive
it at > +-3V with a slow RS232 emulation and hook it to a
microcontroller which does the PWM for you. Otherwise, see a)
c) Frequency multiplexing. You generate an analog signal, which
is the sum of 8 discrete frequencies with variable amplitudes.
You then build a bank of 8 band pass filters + AM demodulators
which gives you 8 analog outputs. The best interface for this
would be a sound card.
d) Time multiplexing. Lets assume you can set up a clocking
scheme (e.g. 5V=clock pulse) It would be just about possible
to use discrete circuitry (monoflops and sample+hold) to latch
the analog values after the 'clock' and drive a PWM or current
control circuit for the LEDs.
e) Value multiplexing. Think binary. If the value is represented
as an 8-digit number, each digit could 'drive' one LED. As a
practical implementation you'll need to run your analog value
through an A/D converter and extract the individual channels
digitally, drive PWM, etc. It will probably flicker interestingly
during the updates. You won't get much more than 2-3 levels
of brightness out of this.
Kind regards,
Iwo