Have set up to activate 8 LEDs using DT800 digital channels based on various alarm conditions. Each is connected to a discrete DSO channel with the opposite end attached to an external 5VDC.

The 5VDC return is connected to the digital ground. Individually the led's illuminate as they should when the state is changed from 1 to 0. However when I try to turn on two at the same time either one is illuminated without the other or both stay off.

Sometimes I'll get an unexpected result where channels 1 and 2 will be switched but channel 5 led illuminates. Again if I reset the system and actuate one at a time everything works. Current draw per led is 10 mA.

FYI, have removed the original program and am just using 8 lines of DSO code and see the same result--think it has to do with hardware/configuration vs. program.

Thanks,
Bernie

Good afternoon Bernie,

Do you have a resistor in series with the LED?
It may be you are shorting the power supply and pulling it low, try putting a 1 kOhm resistor in series with each LED. This will limit the current draw and stop the power supply shorting.

Cheers,
Roger

Thanks, I do have resistors in series with the LED's. Looks like this may be a manufacturing problem with the LED's as I replace them with DigiKey equivalents everything works.

Some of the original LED's required 6 mA but about half of them from the same lot consume 0.05mA! Looks like a source issue vs. problem with the DT800.