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DL-149 output circuits for voltages greater than 5 volts.

Oct 12, 2014
David Mathog wrote
Today I tried to drive the input of an optical isolator wired like this:

+12V - 2KOhm resistor - Optoisolator LED - D0+ (FET) D0-(common) - Ground.

This didn't work - no matter what the state of D0 there was current through the LED sufficient to turn it on. In the diagram for the output lines it shows a 10K resistor to Vbus above the FET. The voltage at dout for X0 was 10.82V, and for dout X1 it was 1.21V. So it looks like when the FET is off the "pull up" resistor actually pulls "down" in this case. When the circuit was rewired to use a +5V supply, then the optoisolator would finally go off, because Vbus is also 5, and so the voltage difference across the LED was zero, or at least too small to turn it on.

My question is, is there some way to configure the DL-149 to disable the pull up resistor on the output? That is, detach Vbus somehow? I was trying to use 12V because the power MOSFET that is the actual device being controlled, one step removed by the optoisolator, isn't saturated with a gate voltage of 5V, but it is at 12V. (The output side of the optoisolator has its drain tied to +12V and the source goes to the gate of the power MOSFET through a 1KOhm resistor.) If push comes to shove I can rewire the circuit to use both +5V and +12V, but it would be better if there was some software configuration for the DL-149 that would do the same thing.

This DL-149 is being controlled as a serial device on Linux, so it can use whatever text commands are available in that interface. I don't recall if this device can be software updated or not, but if so, it certainly has not been updated in several years.
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1 Answer
Oct 13, 2014
Shawn agent wrote
David,

Sorry, there is no software setting to turn off the 5V. The pull-up resistor is soldered on the board.

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Regards,
DATAQ Instruments Suport