Sourcing a Low-Cost, Long-Duration Timer

$10 each perhaps may be possible in 10000 lots.

You will need some kind of power unless it is a mechanical device.

I just trawled through several dozen places and you are never going to get even remotely close to your target price. $40 plus may be. But $0.30 not a hope.

To achieve such a low unit cost I would say you will have to spend a lot on the front end and probably chemical is the only way to make it that cheap. I could design you a circuit that would give you an alert in four years if that's what you wanted but the parts cost would be at least a few dollars in very high volume. Maybe you could make it "re-useable" instead of disposable.

The only device I can think of to remotely approach your price point are cheap quartz watches, which I have seen in $1 vending machines (so their actual cost is probably a tenth of that). These might be configured (no LCD readout required, or 90 day countdown) for a one-time use (tab between battery & contact) with an alarm at the end of 90 days, like those cheezy musical greeting cards, or a blinking LED. There must be a zillion manufacturers of these cheap devices, but where you would start, what sort of volume would be required to reach your price point, and what up-front design costs are involved (reliable function in low/ fluctuating temperatures, condensation, etc. might be issues),I have no idea. But, if I were to have your challenge on my plate, this is where I would start. Or, alternately, you could include, in the instructions for use, "If your fridge stinks after 90 days, replace"... :)

I found this http://www.fairchildsemi.com/an/AN/AN-2002.pdf but have no idea of the price.

Obsolete part.

The Brita water filter pitcher we use at home has that kind of device to indicate when to change the filter. I have no idea the cost or where they get them.

If you want a large distribution you could think about memory-shape alloy switch. I've heard of some alloy that are not reacting with temperature there simply taking their form back in time. Since you would need a great bundle of these pieces, I'm sure it would not be far of your .30$ goal. But I think the cheap watch solution except for the fiability would be better.

I would think that you might want to post this in the Chemical Engineering Forum.

There is probably some time delay chemical reaction that would change color after a certain amount of time.

Have you tried GlobalSpec.com?

Paul Espinoza,

Camarillo, California

I recall a story I heard at work about an engineer who developed a titration device that was cheap and designed to be put into a container with frozen food at which time the bulb containing the titration solution was crushed. When the titration solution thawed it would travel up the paper at a predictable rate and one could tell how long the food was subjected to temperatures above freezing, even if it showed up at the store frozen. Problem was, neither the shipper, the carrier, nor the stores wanted to know.

For your product, perhaps opening the container would rupture the titration solution or put two material into contact with each other where one would slowly disolve into the other. It would travel up the "paper" at such a slow rate, that it would reach the display window after 90 days.

How about a 90-day egg timer? Purely mechanical. You would have to work out issues with regard to ensuring the "sand" or whatever it ended up being continued to flow but hey it's reusable.

I got an idea which may workout for you. Buy one simple counter that counts max 100. Using SUN light give input pulse to this counter and preset at 90; a day light operated relay, which can be build using Light Dependent Resistor and one transistor. Each day will give just one pulse and you have the 90 days timer.Here you may use lever operated mechanical counter and operate the lever with a electromagnet; this do not require continue power.

Dude, SUN light give input pulse, day light operated timer...this is inside a refridgerator? hello? anybody home?

dude? yes when people could not understand Gelilo called him dude???? I gave my idea to have cheap 90 DAY timer. Normal timer use 50Hz or 100 Hz pulses that are divided many times to give seconds, Minutes, hours.. so on. Imagine you have a simple electromagnetic impulse counter and every day at 12 noon you generate a pulse with the help of Sun light operated relay; you get one pulse a day that will increment counter by one everyday till the preset 90 days. In my city one can buy a counter for Rs. 100/- (US$ 2). To get an impulse from Sun light one need not carry the unit to Sun. An open window, vetilation hole or any source that allows natural day light to enter the room (just out side the Refregirator) will serve the purpose. Just make the sencing circuit in such a way that, it gives one one impulse a day. If you are still see me dude....yes, I am...bye..Munky

Dude, where I come from, is considered an endearing term of friendship. But with all due respect, although I must admit to being flippant when I responded previously, I am being quite serious when I say that you comparing yourself to Galileo is nothing short of delusional.

That aside, the point was, since we are obviously talking about a stand alone deodorizing unit placed inside the refrigerator, and not a built-in component, how do you propose to expose the unit to sunlight? And come to think of it, how would the unit know it was 12 noon without a timer?

Here the requiremnt is a 90 days simple timer which will give some audio/ visual indication after counting 90 days. It will cost US$ 2 to 4. Various timer chips available are costly. More than 12 Hour timers are costly and need continue power supply. http://www.nishantengineers.com/htmlsite/sitemap.asp is the link for impulse counter. One photo transistor one MOSFET and few resistors can make a "day sening" circuit (shall cost US$ 0.50). This may be kept out side and carry two core wires to the refegiration unit through 1 mm hole to operate the counter. It is not possible to make it less then US$ 0.30. I have came across Chinese make week timers that are used on "Transfer Molding machines". (I worked in Semiconductor manufacturing for 3 decades), but never come across 90 day timer. These week timers are costly (US$ 10) but require power always.

Timer chip for 30 cents each may be possible if ordered in 10 million numbers. Is that what you want? This may still require DC power source, relay, PCB which is extra. I am sure you don't look for 30 cents timer for your single home fridge. You have engaged more number of hours than 30 cents.

Considering the US$ value of time at $100 per hour for the designers, it might have already exceed $1000 or 3000 timers of your requirements. Make sure you have reason for all that.

OK, here is your timer cicuit for $1.17, not including the PCB or enclosure:

Microcontroller $0.39

Crystal $0.28

LED $0.09

Lithium Cell $0.35

Misc R&C $0.06

I can program it to any delay you want up to the battery life expectancy which I calculate at at least one year. At the end of the time it will begin blinking the LED until the battery dies which could be days depending on the dormant period. I can complete this design for $2500 US dollars. Low power battery circuits are my specialty. The above estimated parts cost is for a build of approximately 5000 so at 100,000 it should drop even lower.

As with many responses to many posts, I think the point is being lost here, if it was ever fully in focus. This is a result of A: The objective not being fully explained and/or B: The right qualifying questions not being asked, before offering solutions. I assumed (something I am usually loathe to do) that because a <$.30 - 90 day timer is being sought, it probably applies to a <$10 disposable refrigerator deodorizer (an upgrade from a box of baking soda). Even under that assumption (which is not unreasonable, given the supplied information), I felt my suggestion of a quartz timer was overkill (from a conspicuous consumption point of view), let alone suggestions of devices requiring holes to be drilled through the body of the fridge, 1mm or otherwise.

I guess my point is, although there seems to be no shortage of technically clever people with vast knowledge, experience and ingenious solutions, what is considerably less common are those who also have the ability to accurately define the problem, and therefore be able to give solutions that actually solve the problem. Communication skills are equally as critical as any other skills, but are rarely as developed. This has been my observation not just here, but in industry as well, at least here in Canada.

One easily mastered skill is to paraphrase the statement/problem/question etc. back ("So what you're saying is..."). You would be surprised how often the response comes back "No, that's not what I'm saying. I'm saying...". It works in a marriage too!

Either that, or there are just a lot of people here eager to display their knowledge and abilities, regardless of whether they are particularly on point or not.

Notwithstanding the good points you make, sometimes, when the requirement is one that may not be attainable, to suggest the closest conceivable match may be useful. I have found many times customers come to me asking for something outrageous and when I suggest a practical solution they are able to then decide if some of their requirements can change to accommodate that which may be doable. This does not necessarily constitute showing off one's knowledge or not listening. I suspect the only way to do this particular application for $0.30 is with a chemical sensor and it may be that there are insufficient development funds to develop such a means. After considerable thought, it occurred to me that it could be done for a pretty low cost and although I, as a result of listening to what the poster had said about the application, did not think that $1.17 would be satisfactory but suggested it in order to offer additional information that might be useful in exploring alternate possibilities. I find that at times there are often posts that would assume to chastise other posters for perceived faults and I would have to say that those posts also do not necessarily serve the original poster well and are in fact sometimes a manifestation of the very quality that would be criticized. Surely I am as guilty as any other in this regard and so I would hope to promote a sense of tolerance and allowance when posts do not immediately appear to be ideal. We all struggle to offer help in our own way and sometimes we are able to do better than other times. Sometimes we don't always see how well or how poorly we have done but at least we are trying. That's how we all learn.

I wholeheartedly agree with you, and if I came across as intolerant, it wasn't my intention. This was a pet peeve of mine long before knowing of CR4's existence. And to be fair, I have picked up useful information from responses that were not necessarily specific to the post in question.

No offense taken. We all have our areas of sensitivity. I had just earlier responded to a "Guest" who had made a rude comment about the irrelevance of a very short post I had made to the wifi RF risk. Rude guest posters set me off sometimes so I may have been a little reactive but appreciate you understanding.

Not a problem. By the way, your Bertrand Russell quote is one of my favourites.

How labour intensive do you want this? How many of these are we talking about? 10, 10000? Timer packaged with product at factory for consumers to initiate timer?

You could always use a chalkboard, with refresh date indicated. or maybe post it notes(90 in pack and rip of one a day). How about tag as we see for fire extinguishers with service date stamped on it. Could use waterproof paper with generic dates on that you can indicated when due for replacement.

Just throwing some ideas into mix. Don't want to dumb down this thread but would consumer appreciate a complicated mechanism for timing?

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NickCarraway16:

I think it is feasible. I have an idea on how to implement it. I have been working on low power timers recently and I came across one such feasibility. As this application is not very critical of exact 90 days, it is more short of 90 days +/-1% type that can solve the problem.