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maintaining signal wire with 5V

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  • maintaining signal wire with 5V

    Good day all,
    I'm working on a school project building an automated vehicle datalogger using an M2 PS. The system logs during driving and charging, and when finished has some file maintenance and other tasks to complete before shutdown. As such it can't begin shutdown as soon as ignition wire goes low. We'd like to turn on an output during program startup which holds signal high, then when all functions are complete (a couple minutes after ignition off) we'll pull the output low and exit.

    We're already using an NI USB-6009 box, which has digital and analog outputs, but only up to 5V. Our experiments with transistors and MOSFETS always result in lower voltage on the device output than at the gate or source, i.e. lower than the required voltage on the signal wire. We currently have a reed relay driven by analog output which seems to work okay, except for it pushes the current capability of the analog signal channel on the 6009 and we're not sure about reliability from vibration and temp changes. Any ideas on how to step up our voltage to the signal wire threshold?