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Radio Shack once again saved the day — Parallax Forums

Radio Shack once again saved the day

Beau SchwabeBeau Schwabe Posts: 6,566
in General Discussion
Radio Shack once again saved the day .... The sign out front says "3 Days and we're gone ... everything must go ... office shelves, cabinets, furniture must go" .... So what do I go in there to buy? .... A Reed Relay for $1 that I was going to take apart anyway.... I just needed the Reed switch to make an electronic float sensor for a bilge sump pump. ... What's a Reed Switch in case you asked? Literally two thin pieces of metal (Reeds) that are separated by a millimeter or so in an insulated glass capsule. When a magnet is in their presence they become attracted to one another making an electrical connection. Placing a magnet on a water float creates an electrical means for detecting the water level.

Comments

  • MikeDYurMikeDYur Posts: 2,176
    The next time that happens, you will be forced to shop at the local hardware store, and buy a ready made hermetically sealed level switch with the plug and socket attached. I guessing $40.00, if they have it. The hardware store may have to stock some of those items you would normally go to RS for. What is a handyman supposed to do these days?
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2017-05-30 00:40
    Or you could get an alarm system window/door switch which contains a magnetic reed switch.

    Back in the 70's I built a homemade car alarm system and wanted a hidden switch to turn it on/off.

    I glued a small magnet to a reed switch (see one on left).
    Another magnet would allow it to act like a toggle switch depending on which end I touched it to.
    Tucked it in a corner of the dash by the windshield .
    Held the "triggering" magnet on the outside of the windshield to arm or disarm - worked great!

    Pretty sure I bought these at Radio Shack

    Reed%20switch.jpg
    Reed switch.jpg
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  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2017-05-29 18:51
    My first thought was a alarm window/door switch, but all I could find were wireless versions ... I couldn't justify spending $50 on something I could get for a $1.
  • ercoerco Posts: 20,256
    Ha, I hit up dollar tree for window alarms the last time I needed reed switches. For a buck, you get it all: reed switch, magnet, 2 or 3 button cells ( I forget) and a LOUD alarm.

    Nice to hear from Sir Beau!
  • MikeDYurMikeDYur Posts: 2,176
    edited 2017-05-29 22:48
    erco wrote: »
    Ha, I hit up dollar tree for window alarms the last time I needed reed switches. For a buck, you get it all: reed switch, magnet, 2 or 3 button cells ( I forget) and a LOUD alarm.

    Nice to hear from Sir Beau!


    Are these the same ones your talking about?

    I nabbed a bunch a long time ago. As you can see, I have been into them.

    BTW: What is under the blob?
    20170529_184056.jpg
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  • SeairthSeairth Posts: 2,474
    MikeDYur wrote: »
    BTW: What is under the blob?

    It's an IC. I think it's called something like chip-on-board, where they just glue the wafer to the PCB and wire bond it directly.
  • kwinnkwinn Posts: 8,697
    edited 2017-05-30 00:08
    Seairth wrote: »
    MikeDYur wrote: »
    BTW: What is under the blob?

    It's an IC. I think it's called something like chip-on-board, where they just glue the wafer to the PCB and wire bond it directly.

    Yep, chip-on-board, aka COB. A lot of early digital clocks and calculators used COBs.
  • MikeDYurMikeDYur Posts: 2,176
    Seairth wrote: »
    MikeDYur wrote: »
    BTW: What is under the blob?

    It's an IC. I think it's called something like chip-on-board, where they just glue the wafer to the PCB and wire bond it directly.

    Yes, I have seen them before in low cost products. This just seemed like an over complicated circuit for what it does, unless it holds it's state after being triggered. I don't think I even tried them, before I dismantled them. Probably a 555 type design of sorts. But that nice looking Inductor has me baffled.
  • SeairthSeairth Posts: 2,474
    MikeDYur wrote: »
    Seairth wrote: »
    MikeDYur wrote: »
    BTW: What is under the blob?

    It's an IC. I think it's called something like chip-on-board, where they just glue the wafer to the PCB and wire bond it directly.

    Yes, I have seen them before in low cost products. This just seemed like an over complicated circuit for what it does, unless it holds it's state after being triggered. I don't think I even tried them, before I dismantled them. Probably a 555 type design of sorts. But that nice looking Inductor has me baffled.

    Maybe this?

    http://www.homemade-circuits.com/2012/04/simplest-piezo-driver-circuit-explained.html?m=1

    (tl;dr : volume boost for piezo speaker)
  • MikeDYurMikeDYur Posts: 2,176
    edited 2017-05-30 13:42
    Seairth wrote: »
    Maybe this?

    http://www.homemade-circuits.com/2012/04/simplest-piezo-driver-circuit-explained.html?m=1

    (tl;dr : volume boost for piezo speaker)

    Totally forgot that it is a piezo speaker, and has to be driven by frequency. It was right in front of my face the whole time.
    Wonder if these same inductor's can be used in a charge pump circuit. I have some Maxim chips I can play with.
  • ercoerco Posts: 20,256
    Yup, that's them. A good deal for a buck. Those things are LOUD. The reed switches are very fragile though.
  • MikeDYurMikeDYur Posts: 2,176
    erco wrote: »
    The reed switches are very fragile though.


    Yes, it's best not to try to bend the leads strait.
    The leads are usually a heavy stiff wire, and will bust the end of the glass capsule. If you keep a firm grip on a pair of needle nose close to the glass helps, if you really must bend. Lost a couple scavenged reed switches trying to manhandle them in the past. Some of them are pretty small, thin glass package.
  • KeithEKeithE Posts: 957
    https://www.dollartree.com/Battery-Powered-Window-Alerts/p328789/index.pro

    Seems like kids could have a lot of fun with these. I guess you could even tie strings to the magnets and setup tripwires.
  • localrogerlocalroger Posts: 3,451
    Lifetime supply of reed switches for ten bucks...

    http://www.goldmine-elec-products.com/prodinfo.asp?number=G21009A
  • ercoerco Posts: 20,256
    MAN, I better install these window alarms in my own house! We had a break-in and car stolen just last night two doors down. Two 18-year-olds from Colorado, one a murderer, randomly ended up in my city, on my street of all places. ~11:30 they broke in (fortunately the sweet elderly couple wasn't home), stole their car, then drove to another house 2 miles away and broke in, beat up an elderly widow of a local police officer. Torrance PD nabbed & grabbed these degenerates. Big news in our normally quiet 'hood. Channel 4 news just interviewed me, not that I had much to tell.
  • KeithEKeithE Posts: 957
    Erco - you could have mentioned Dollartree on the news and started a run on window alarms.
  • ercoerco Posts: 20,256
    edited 2017-05-31 03:58
    Local news story at http://www.dailybreeze.com/general-news/20170530/denver-homicide-suspect-arrested-in-torrance-home-invasion-robbery-beating

    Also http://losangeles.cbslocal.com/2017/05/30/woman-attacked-torrance/
  • Beau SchwabeBeau Schwabe Posts: 6,566
    Ok, so the underlying reason I needed a bilge pump .... ... The irrigation control valve is leaking. (<-- Read was buried about two inches below the surface and the riding lawn mower ran over it all by itself <smirk> ) At least it is not the well pump that is leaking. I'm pretty sure of that. I still need to wait for the surrounding area to dry up before I begin to investigate further. I had to create essentially a sump pump to lower the water level, so daringly I got out my gas powered post hole digger with the smallest auger (6 inch diameter) and sunk a 2 foot hole near the well head .... fortunately I didn't hit anything but dirt and clay. I found a 12 Volt bilge pump at Academy in their marine section for $14 ... I was able to fit the pump inside of a 4 inch diameter PVC pipe and use an inner cap to seal one end. I constructed my own electronic float valve and placed that inside of the PVC pipe.... about 6 inches from the bottom of the pipe I drilled 3/8 inch "inlet holes" all the way around the pipe. Powered from an old Laptop power supply and with an attached garden hose re-directing the water to a drainage ditch it works like a champ... just waiting for the ground to dry up a bit before I proceed but rain seems to be in the forecast Ughh!!

    ICV.jpg
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2017-05-31 05:50
    Erco,

    I ended up not having to remove the reed from the relay (not to break the glass on the reed switch ... been there before as well), the magnet was able to trigger the reed with everything else just left intact... but notice the orientation (Aside from the image needing to be rotated 90 CW)... notice the orientation between the magnet and the reed switch. This approach was ideal for the type of sensor I needed and to streamline the overall sensor layout.

    BTW, the reed switch is driving a relay which in turn energizes the motor.... the reed switch is NOT directly driving the motor.

    One thing to note: with a pump like this there is very little hysteresis, so if there is any back flow when the motor turns off, then it will oscillate as the water rises and falls. Ideally you would have TWO float sensors at different levels to increase the hysteresis. In my case however I got away with one sensor because the bilge pump serves to prime a gravity siphon .... once primed, the pump doesn't even run, the siphon takes over... if the siphon fails, then the pump will prime it again.


    FVWB.jpg
  • MikeDYurMikeDYur Posts: 2,176
    Wow erco, When "Prop 57" was mentioned, I thought they were looking for one of your inventions. It's an uneasy feeling having that level of crime so close to home. You need more than a window alarm.
    Hopefully things will quiet down again, and this is not a sign of our times.
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