How to make a minimum hold circuit?

[Sostratus]

Trying to design a circuit that monitors an input and remembers the minimum observed value. If it works, it will be a useful tool for checking if other builds are doing what I expect.

I tried a 3 combinator setup (plus a 4th to make the input generic). There's an arithmetic combinator acting as the memory cell to hold the minimum. There's an arithmetic combinator subtracting the stored minimum from the input. And there's a decider combinator which, if the difference is negative, injects this difference into the memory cell. First I initialize the memory cell to some arbitrary high value using a constant combinator before I connect it to the rest of the circuit.

I thought that would be all I need, but in practice it over-corrects and drives itself down to negative values. Maybe it's some kind of propagation delay issue? Any ideas how to solve it?

Blueprint of my prototype:

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[feng]

I also could need something similar, so I gave it a try.

grafik.png (119.81 KiB) Viewed 659 times

It works on single tick base. Saving the lowest value of multiple signals, also if signals disappear from input.

Consisting of 3 groups:
- lowpass filter (left decider): comparing memory cell signal with input.
- memory cell (upper decider) + arithmetic combinator (center) for updating the memory cell by adding the difference of memory cell value and input value.
- loopback (lower decider): looping back memory cell values into memory cell if one of the input signals become 0.

Green input of lowpass filter is your input for your signals.

Hope it works for you,

Cheers

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[BaggyK]

It is possible with two decider combinators. Using red wires link the outputs of both combinators, to the both inputs of the combinators. Using green wires link the inputs of both combinators together. Then also link the outputs of both combinators together using green wires.

One combinator setup if item on red <= item on green or item on green = 0 then output item with count from red.
The other combinator setup if item on red > item on green or item on red = 0 then output item with count from green.

In other words, output smallest value (ignoring zero), with feedback on red to hold last value.

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[Sostratus]

Thank you both! The two circuits seem to agree on their results. BaggyK's design has the advantage of being smaller, but feng's design appears that it could be used for an arbitrary number of inputs.

Changing it to a maximum hold circuit on the 2 combinator design was as easy as flipping the less thans and greater thans. Have to think about some more how to convert the 4 combinator design.

Some background, my plan for this was to watch a buffer on Gleba, which I want to be as small as possible to minimize spoilage but not to be empty to ensure demand is being met.

[Zaflis]

Remember that you can use selector combinator to output the smallest signal from all input signals, no matter how many. I'll assume the memory cell will be the attached decider combinator to it then.