The reason for 16mA is the opto-isolators we use (HCPL-2531) are fast but have low gain (collector current vs. LED current). The minimum guaranteed is 15%, typical is 30% while maximum gain may be as high as 50%.

The opto collector current load is 2mA which makes the worst-case LED current just over 13.3 mA (Ta = 70C, Vcc = 4.5V, 15% gain part).

Trouble starts when you look at the "typical" and "maximum" specs. The result is most drives work satisfactorily with 6.6 mA while the best will work with only 4 mA. This is the reason some people get away with using 74HC or 74LS logic series drivers. They get away with it until they run into an opto that is near the minimum spec.

By the way; I can heartily recommend Arturo's breakout board for use with our drives. It is a well-designed board.

10m and 15m ??? It must have been during daylight hours or meteor-skip conditions I'm guessing.

Mariss