Acquire multiplexed LED states

[Rash]

I am trying to acquire the state (on or off) of a multiplexed LED, I have tried measuring with DMM4060 but failed I have tried sampling/triggering with a DIO6533 but failed. The reason for the failure is because a multiplexed LED only comes on for a very short time (say 1ms) many times a seconds such that the human eye sees LED as continously on but sadly the DAQ card don't.

[rgharrison]

Hi Rash,

It could be that both hardware products were not necessarily ideal for the type of measurement without some signal conditioning. What I mean is that the DMM4060 can not achieve the rates necessary to sample a diode switching at rates in the kHz (1ms period). It could also be the voltage generated by the LED (or current) was insufficient to register as a "on" or "off" state with the DIO6533.

The 6533 is definitely capable of switching at well over 1kHz. It can detect logic voltages switching at 20MHz (50ns period). The reason the 6533 could not detect the state of the LED is probably because the voltage applied to the input of the card didn't exceed 2V or the current was insufficient to drive the logic level (at least 40uA).

The datasheet f
or the LED should give the electrical characteristics of the device. From these specs, we can determine how we can properly measure the LED with the 6533.

What Is the Definition of a TTL (Transistor-Transistor Logic) Compatible Signal?
http://digital.ni.com/public.nsf/websearch/ACB4BD7550C4374C86256BFB0067A4BD?OpenDocument

Hope that helps. Have a good day.

Ron

[Rash]

hi Ron,
Thanks a lot. I have fixed the problem using dio6533 and some kind of integrating hardware, out of curiosity if I am to use the DMM4060 you suggested what kind of signal conditioning will I need ? Do you sell them ?
Ta