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what is this part?!

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New Member
Hi all again! This evening I am just sitting around and working. I keep looking up at this part that has been sitting around on my desktop for at least the last 2 years, maybe more. I wonder what it is!

It appears to be a photo-resistive device- I say this because it slightly resembles one structurally. As well, I've tried a few resistance measurements and it does appear to change when I cover the sensing area.

The package itself it what confuses me! It looks like the contact portion of a mass produced button (the contacting membrane I guess) and is laid out on what appears to be ceramic. The ceramic is then also laid onto a steel slug, like a sink almost,, although I suspect it is for mounting rather than diss. 2 leads, and thats about all there is to it. I'm still confused. Anyone familiar with these types of devices- is there any info somewhere I can check out?

any help= much thanks; jd


Grant Fleming

New Member
Where sort of equipment was it likely to have come from?
Has it any part numbers on it?

More to the point....who the hell put this thing on your desk? That is so cruel!




New Member
mystery part--

yeah I have been trying to think of were I got it from. I think maybe a toy robot or something,, if not maybe a camcorder? It has literally been sitting here for at least 2 years collecting dust. I pick it up every now and then just to have a look. I've always thought it was just part of a button.

Maybe the 'sink' is there to help mount as well as 'regulate' temperatures from surrounding components from affecting its function if it is indeed a resistive element? When I took the measurements this morning I tested once under daylight (0v) and then again covered with my thumb (0.02V). The resistance changes as well from about 1k to about 1.2k covered.

A while back when I was doing some research about photo-cells and other light sensors I came upon an article that talked about other kinds of materials used to fab photo-resistors, so I know that they do not all appear like the cheap and common ones we usually encounter, but the article did not link to any other types or show an example so I have no idea what to look for.

What else could it be tho? I'm going to test against a typical cds cell tomorrow and see how they compare in voltage variations and also resistance, that should prettymuch firm things up some more. Perhaps this type is more sensitve, or faster.

No, its not from the FBI or CIA,, I already found their plants' ;I >>jd

>>ps no part #'s


I could be wrong but it looks very much like a DEW sensor from a video recorder,
try holding it in some steam from your kettle and see if the resistance changes.


New Member
component idedtified!

Yeah I think the last 2 posters have it right!! I did the moisture test this morning and the resistance of the deivce went up in large multiples- ie. dry and uncovered it read about ~1K or a bit less, with a nice misting of moisture it went up drastically (I think about ~100K).

You know, I never even considered that it was a moisture sensor! When I think about it there is a very likely chance that the device came out of an old VCR or an very old camcorder. It has been so long.

Thanks to all who have helped out- helped me to put this mystery to rest! regards, jd


New Member
yeah, again I'm unsure where it came from exactly. There are only certain things it could have come from tho- because I tend to only keep certain salvage electronics- all of which are really intended to be indoor only applications so who knows why or from what it was taken from!? I can only assume that it was a camcorder or similar because it was in a pile of related bits. My other thought is perhaps a toy- I've always been a collector & destroyer of toy robots and similar--jd

Nigel Goodwin

Super Moderator
Most Helpful Member
Gaston said:
old vcrs were used out on the lawn or something?
You obviously don't know anything about VCR's :p

The head and drum assembly is a fairly large chunk of metal, so if you take the VCR from a cool place to a warm one, then you can often get condensation on the head and drum.

When you put the tape in the VCR, and the tape is threaded around the drum, the condensation causes the tape to be ripped apart and wrapped around the drum. As well as destroying the tape this can also quite easily smash the heads off the drum.

So VCR's commonly had moisture sensors mounted on the drum, which disables the machine unless it's dry - USUALLY!!!.


New Member
another one!

well I was farting around in my toybox last night and came upon another one! Check it out,, this one I am 90% sure came from a toy robot,, the two modules each have a photo-reflector unit so I was keeping them for an edge detector pair for sumo or something. One module may need to be slightly modified but they are basically ready to plug in, so deemed 'keepers'. Oddly there is also one of the mystery (dew) sensors, a smaller one tied into the wire harness of one module (the other side has an additional switch) and sharing its connector (oh well, still a good find).

In this app I wonder why a 'dew' sensor would have been required. jd


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