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Substitutes for mercury switches

Substitutes for mercury switches

Substitutes for mercury switches

With the need to remove mercury from many industrial applications, what are the  substitutes for mercury switch applications?


RE: Substitutes for mercury switches

hi...can you please give more details...
are you using the mercury switch for HIGH ARCING applications?

can you name few applications?


RE: Substitutes for mercury switches

In reply to dydt....

I just got an email from a friend who is working with disabled children making "toys" that aid in their making more use of their limbs. For instance, he writes, "By using several mercury switches, you can vary how high the child’s arm must arc before the toy turns on." He's coming up with low-cost ways that are alternatives to conventional therapy.

From this I would gather that we're looking at low voltage/current applications.

RE: Substitutes for mercury switches

The same could be done using the microswitches and as per requirement the position of the switch could be adjusted to vary the arcing of the arm of the child.

RE: Substitutes for mercury switches

My friend's daughter has cerebral palsy, is a quadriplegic, and non-verbal. He is also a single parent. Because there was little on the market in the way of equipment that fit her needs and because "experts" wanted around $200/hr, he saw a need for simple, low-cost equipment for her and other disabled people. Since he is using mercury switches from old thermostats, etc., I thought I would see what might be available for substitutes without mercury.

If anyone can offer some ideas - alternatives to low votage/low current mercury switches - I'd appreciate it.



RE: Substitutes for mercury switches

It seems like you could build a cheap position switch that would take care of your needs by building something like a pendulum in a can, or like a bell.  Isolate the "knocker" of the bell from the bell itself.  When the "bell" is upright, there is no contact.  When the bell is tilted, the "knocker" hits the side.  Attach wires to both the "bell" and the "knocker" and you'd have a position switch.

Another idea:  rip open one of those dolls that close their eyes when they lay down.  Duplicate their design, or rip out one of the eyes (sorry for that gory picture) and attach a small proximity detector (maybe a magnetic switch) to the eyelid.

Yet another idea:  most irons are designed to shut off if they tip over.  Rip open an iron and see how that works.

One last idea:  electronic gyroscope or compass from Radio Shack.

RE: Substitutes for mercury switches

Sorry to hear about your freind's problem. Mercury is  a big problem.   There are lakes all over the country ( including Lake Michigan where mercury pollution is  a problem, there many warnings about eating fish from such places.  There is  a reason that you cannot buy mercury swithches any more. The dangers of using it and it's impact on the envrioment are well documented.  Look up the origin of the phrase " mad as a hatter".   It puzzles me that a responsbiel person can  use the stuff in amaturish uses.  Your original post had to do with "industrial applications" not "toys" for handicapped kids.

RE: Substitutes for mercury switches

Check this site for details on low cost electrolyetic tilt sensors.  While they don't cost a lot their use is not straight forward and they may not be practical for your friends use.  

A more pragmatic approach might be to minimise the hazards of mercury switches (breaking and releasing the mercury) by potting the switch in epoxy or similar.


RE: Substitutes for mercury switches

BrianR - Thanks

I'll forward the link to my friend. Looks good.

He does pot the switches. In his mail to me he said, "Sometimes there’s no control devices that are available, so I had to make them myself. A mercury switch encased in an aluminum tube, sealed with hot glue or epoxy is a handy switch to use...."

Thanks again.

RE: Substitutes for mercury switches

I'm the one who's daughter is disabled. The mercury switches I use are placed in steel or aluminum tubes then are sealed with hotglue or epoxy. There's little worry about leakage since they're sealed. Granted, what can be sealed can become unsealed, but you are really going to have to work hard at unsealing these. Irresponsible, no. Ignorant, only if you think I'm going to be irresponsible with such materials.

In my area, mercury switches are easy to get. I can get them at Radio shack, electrical industrial warehouses, and just about any where else that serves an industry that needs such things. However, I am open to using something less hazardous than mercury because it’s my preference. I had considered using a small ball bearing, BB, et al in a metal tube with a contact at one end. However, there’s the arcing factor that could make the toy stop working. I’ve considered using nitrogen to keep the carboning of the contacts, but I’m not sure if this is worthwhile if there’s something else that’s readily available. Also, injecting nitrogen may be more work than it’s worth.

  The advantage of the mercury switch is it’s not direction sensitive. You don’t have to be concerned if the child is holding the device correctly. If there’s something else that’s off the shelf, I’ll be most appreciative to be informed.

RE: Substitutes for mercury switches

why won't a microswitch work?

RE: Substitutes for mercury switches

Microswitches are positioned at limits. What we're trying to do is encourage the maximum range of motion in the child. Without limits, the child may exceed the expected ROM. Also, the mercury switches can be hidden in a toy and not look like a piece of therapy equipment. These children want to play with toys like every other kid. They're sick and tired of being faced with equipment that looks like something out of Marcus de Sade's basement. With therapy equipment, these kids shut down mentally. As soon as they see a toy, they open up and start playing.

RE: Substitutes for mercury switches

These tilt sensors seem to be the ticket for what I'm doing! Are they self supporting or do they work in conjunction with something that decipher the sensor's signals? I'm going to have to look into these things. Price is also a consideration. Some of these parents are strapped for cash because of the cost of therapy, equipment, et al. The cost of a manual wheelchair can run well over $1400. A power chair can cost around $40,000. Some of these parents have trusts for their child. Some have only insurance. In either cases, the parents have to pay out of pocket because the equipment isn't covered under the trust contract, and the insurance won't cover what they call "experimental" equipment. Quite often, I either give the toy to the kid outright or I charge only for the parts. I can afford to give away only so much. There's been times where I make less off this than what I make because these kids' needs. If the costs are low, I can afford get more of these pieces of equipment to the kids.

RE: Substitutes for mercury switches

I think that electrolyetic tilt switches are relatively high impedance devices that vary their resistance according to the tilt angle so they may be used to measure angles.  A simple electronic circuit would be needed to condition this to control something else.  For example, I reckon that a piezo beeper needing a 3-4kHz drive could be switched directly by an electrolyetic device.  

A general scheme like this should work and be very cheap.  Make a simple CMOS oscillator using 3 gates from a hex schmidt trigger inverter.  Feed the oscillator output through the electrolyetic sensor to the 4th gate which acts as a buffer and drives the beeper.  Parts count ~$1.00

Generallty though there will be some conditioning circuit needed.

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