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digital I/O problem with USB-2408-2AO



Using Daqami, I can toggle on/off the digital ports when the internal jumper is in the default position (all ports at 5V in the off position, and 0V in the on position) but not when the jumper is placed so that the normal digital out is 0V.  I need to send an outbyte to energize each digital port to control solid-state relays (for downstream solenoid and light controls) and cannot have all the relays close as soon as the DAQ board is powered up.  How is that done with the 2408 board?

Secondly, can this be done using the UL library in VB.net?

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The digital outputs on the USB-2408 are of the open-drain configuration, which is similar to the transistor open-collector. An open-drain FET transistor has no ability to drive to voltage level. If you're controlling relays, connect one side of the coil to +V and the other side to the output. Make sure your +V power supply ground (-V) is also connected to the USB-2408 ground. In this configuration, the FET transistor will act like a switch. When switched on, current will flow from +V down through the output back to -V. When off, the output will pull up to 5 volts turning the relay off.

Also, check to see if your relay has a reversed bias diode across the coil to prevent coil current from damaging the output when switched off. See the following: https://electronics.stackexchange.com/questions/110574/how-to-choose-a-flyback-diode-for-a-relay

Best regards,


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