Detail

There are two constant chests, representing the Input signal on the left (I am using the dummy Blue signal, set to the number of iron plates that I need), and the Reset signal on the right (which would be a "Master Reset" switch and needs to be set to dummy signal B to reset the circuit).The Smart chest (lower left) is where the iron plates would be stored.The other components, going anti-clockwise from the top left, are:Decider "Blue > 0", "A =1" (turns the circuit on when a 'Requirement' signal is received)Decider "Iron Plates = Blue", "B = 1" (turnrs the circuit off when Requirement is met)SR Latch (2 identical Deciders each wired with their output to the other's input) set to "A > B", "A = 1"Lamp to indicate on/off status (this would be wired to the actual smart inserter loading the chest)SR Latch set to "B = 0", "B = 1"Arithmetic Combinator set to "B * -1", "A" (when the second latch activates, this nullifies the original requirement signal so that the circuit doesn't turn back on again if the chest is emptied)Wiring is as follows, and is all red (the green wires are only used for the latch 'internal' wiring):Constant #1 Output to Decider #1 InputConstant #1 Ouput to Decider #2 InputDecider #1 Output to Latch #1 Input A (upper)Smart chest to Decider #2 InputDecider #2 Output to Latch #1 Input B (lower)Decider #2 Output to Latch #2 Input A (left)Latch #1 Output (lower) to LampConstant #2 to Latch #2 Input B (right)Latch #2 Output (right) to Arithmetic InputArithmetic Output to Latch #1 Input A (upper)Apologies, as the wiring would have been slightly clearer if I had put the Arithmetic Combinator with the Input at the top instead of the bottom.I haven't seen another version of this, although I am sure that it will be out there somewhere, but I hope that by posting it here it will help other players new to the Dark Art of Factorio combinators to settle in to building some useful and fun automated production belts.Any questions, comments or suggestions for improvement will be gratefully received!