Why Does My USB-6501 Not Output a 5 V "On" voltage?Hardware: Multifunction DAQ (MIO)>>Portable>>USB-6501
Problem: When I output a digital signal on my USB-6501, the "on" voltage is less than 5V. Why is this? Solution: There are two likely causes of this behavior. Because the USB-6501 gets its voltage from the USB, the digital output voltage is dependent on the bus voltage. This may vary from one motherboard manufacturer to another, but the USB 2.0 specifications state that the valid range is from 4.4-5.25 VDC. In addition, when driving large loads, it can become necessary to incorporate an external resistor between the 5 V bus and the digital output line. This allows the USB-6501 to drive up to 8.5 mA of current to a load. As seen in the diagram below, the external resistor is in parallel with the 4.7k on-board resistor. The addition of this user supplied external resistor allows the digital output line to be pulled up to the 5 V rail.
Instructions on how to select the appropriate value for the external resistor is included in the user's manual attached below under the Digital I/O section. Related Links: Product Manuals:USB-6501 (Version 7.5) Attachments: 
Report Date: 09/15/2005 Last Updated: 10/31/2005 Document ID: 3PEC5B8T |
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