You have to change your thinking on this one a bit. The sensor is the source of the signal and so the sensor is driving the line. So in that case, the sensor is the control source and the Photon is the motor. This is a decent document: http://www.energiazero.org/arduino_sensori/arduino%20irf520%20mosfet%20driver%20module.pdf.
You would have to hook up the signals as such:
GND = Shared common ground.
Sig = Sensor PWM output
VCC = Sensor +5V (could be a common +5 from Photon Vin but at 70 feet that voltage will drop)
V+ = Photon analog in pin (i.e. any of the “A” pins)
V- = Probably not needed since you can’t “reverse” the Photon like a motor.
VIN = +V
GND = Shared common Ground.
Now with that out of the way, I don’t think this is the driver that you need. At 70 feet, you want a higher voltage than even +5 volts. The driver you have selected is a motor control driver which will provide a higher current drive… not higher voltage. I suggested some line transmitters/receivers in this post.
EDIT: see notes from @ScruffR on pin usage. Choose “A” pins wisely. Your PWM signal will probably be read from a sensor library or some other means so I was mistaken on analog readings.