> The speed of the FST3253 in the QSD circuit might be a problem above 10m but it would be worth a try.
Hi Tony and Francesco, If you are going to swap to the ACT74 part, you should also consider shifting the capacitive coupled pull up/pull down threshold. AC parts are centered at 2.5V (for 5V VCC) whereas most ACT parts are centered at 1.5V for input threshold. I would change the 10K / 10K ( R11 /R12 ) to something like: 10K / 4.7K or so. 73, Mike Collins KF4BQ
