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Topic: Looking for help with what I believe is very simple. Is it? (Read 1 time) previous topic - next topic

gdoot

Hi wvmarle, the marking on that chip says "RGB-TY-ILS"

cedarlakeinstruments

I disagree that a 555 is a good choice here. It's great for short intervals, but 3 hours is stretching it. The circuit requirement is basically a retriggerable one-shot with a 3-hour interval. My first choice would be one of the super-cheap 6-pin microcontrollers.

@OP: how many of these do you plan to build? At quantities < 1,000 it may well be cheaper to buy the existing assemblies (find something on Alibaba) and change out the electronics than to design & build a mold.

Take a look at Protolabs: they focus on prototype quantities, but I think they may also provide pricing for larger volumes.

Maybe a 555 is still the best way to go. There are many variants of the chip and it costs very little. If the task is a simple as described and production cost is to be low, it would be better. There are plenty of sample circuits. Just google 555 timer.
Electronics and firmware/software design and assistance. No project too small

wvmarle

Moulding the case is indeed costly in smallish quantities.

That chip marking I don't know, quite certainly not a 555 or it'd probably be marked with at least those numbers.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Paul_KD7HB

Moulding the case is indeed costly in smallish quantities.

That chip marking I don't know, quite certainly not a 555 or it'd probably be marked with at least those numbers.
The OP should get a copy of the old "IC TIMER COOKBOOK" and study it.

Actually the cost of molding the case would only be pennies per each, AFTER PAYING FOR THE MOLD FOR THE FIRST PIECE!

Paul

gdoot

It's great for short intervals, but 3 hours is stretching it.

@cedarlakeinstruments, I may be able to make it a 2-hour auto shut-off, instead of 3 hours.  Would that change your opinion at all, or is 2 hours still too long for a 555?

Paul_KD7HB

For longer times, as I recall, a dual device, a 556 or ? was used.

Paul

cedarlakeinstruments

Honestly, I don't know. I do know that it's not very reliable (in my experience) beyond 10 minutes or so. Above that, the resistor & capacitor sizes get fairly high, board cleaning can be an issue because of leakage currents, and you need to use low leakage capacitors.

The only advantage to the 555 in 2020 is that they are absolutely dirt cheap: first page of google reveals qty 50 for a lot price of $1.10 on AliExpress, so that's just over $0.02 each! However, you can't get around the need for high quality passive components.

My suggestion is to buy a handful of 555's, calculate the necessary R & C values and build a few timers and see how it works for you. All the speculation in the world won't beat half an hour at the lab bench!
Electronics and firmware/software design and assistance. No project too small

wvmarle

A 555 is relying on RC timing, which indeed is not reliable for times longer than about 10 mins.

Resistor values get big to reduce charge current and allow not so crazy big capacitors, at the same time capacitor leakage may become as much as the charge current... 3 hours is a VERY long time for an RC circuit!
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

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