James For all our experiments we only use the high level signal taken from the external loud speaker’s jacks. The 50 to 500 mW infrared laser need about 300 mW LF on its modulator to give a perfect squared signal from 20 Hz to 300 Hz. For the LED tests we use a very simple schematic with a saturated bipolar transistor from the same output. 73 Yves F1AVY