magneticssensorswitches
Why are reed switches made in glass tubes?
Reed switches sense magnetic fields, and glass is not the only material not affected by a magnetic field. They can use plastic for example. Why are most of them in glass?
This question came into my mind when one of them easily cracked and then broke. It could have been in a plastic tube; then it wouldn't have broken.
Also, plastic would be cheaper than glass, and easier to melt and form.
Why is this switch so expensive?
What other options are there for a NO pull cable switch? I'm open to ideas of building my own switch.
Many switches can be used as a pull switch depending on the specifics of your application. Something as simple as this can have a string tied to it such that the switch actuates when the string is pulled.
If you need the cable to break away from the switch, there are plenty of mechanical ways to accomplish this. A breakaway lanyard is made to open at a certain tension. There are also more repeatable "tension fuse" type devices based on magnets for various applications; take a look through a big industrial catalog for ideas.
I think using 2 digital inputs is the way to go, but absent that, you want to build a 2-bit Digital to Analog Converter.
This pic, from http://tabatha.esg.utulsa.edu/digital/pages/r2r-alt.gif, shows a 3 bit converter. You would simly omit the bottom bit, leaving off the 2K resistor at V1 and the 1K resistor attached to it.
You won't get your table, but you will get unique voltages for each bit. For this 2-bit converter, if your switches provide 5V, one bit will add 2.5V to the output, and the other will add 1.25V. So, none on would be zero volts, if the switch attached to the LSB is on and the other off, you'll have 1.25V, if the switch attached to the MSB is on and the other off, you'll have 2.5V, and if both are on you'll have 3.75V
Your issue with this approach will be implementing it with SPST reed switches. You may need an op amp buffer on each one.
Best Answer
Glass is clean, dimensionally stable and very strong, doesn't outgas at the operating pressures in the interior of the capsule, won't react with the fill gas in the capsule, and doesn't soften under soldering temperatures.
Here's a beautiful link.