An industrial process variable transmitter includes a process variable sensor configured to sense a process variable. Measurement circuitry is coupled to the process variable sensor and provides a measured output as a function of the process variable. Output circuitry includes a loop connection configured to couple to a process control loop. An optical sensor receives the measured output from the measurement circuitry. A switching device applies pulses to the process control loop in response to an output from the optical sensor. Power supply circuitry powers the optical sensor, a comparator, and/or the switching device with power received from the process control loop and loop connection.