Why does my Sealevel Digital I/O TTL adapter have 5 volts present after system power on?

  TTL I/O devices are commonly used to control solid-state relay modules that interface a variety of input and output devices.  An important consideration in these applications is to make sure that the solid-state outputs are properly configured before being energized. Solid-state relays operate using negative logic, where the off state (logic 0) is 5V. […]

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