In the last picture is shown a common type of ‘smart loader’. It can’t detect when the flow of items through the hopper stops though, which prevents it from releasing a mine cart if the cart’s slots aren’t all full. In the first and second picture are a modified version I made to solve this issue. This has it’s own flaw though of a much increased footprint due to my difficulty routing the signal from the second detector rail comparitor back into the first detector rail comparitor. One more flaw is the increased quantity of required comparators.
My version still uses the hopper detecting comparator to power the sticky piston that captures the mine cart but it’s release override isn’t based on comparing the signal from the mine cart to a 15 strength signal like the normal design, it instead compares the signal of the minecart as a container to it’s self utilizing delay. A hopper takes 4 redstone ticks to move an item and the comparitor ads delay of 1 tick (according to the wiki) therefore, by adding 5 comparitors for delay feeding Into the side of the comparitor that sends the override signal it can detect when the minecart stops filling without being affected by the 4 ticks in between an item flowing into it
by jizzycummings