Failure mode of cheap wireless doorbell chime pushes

Hi all has anyone done any exploratory/repair work on these sort of things? You know the ones, they operate in the 433MHz band I think, and you set some DIP switches on both bell push and receiver so that the codes match.

I know they are cheap rubbish, and the attrition rate is high; nevertheless I am thinking of taking a closer look at one that has stopped working. My first guess was imply that the press switch had failed; but it's a PCB mounted switch with an ON resistance of 50Ohms, which seems at least hopefull.

There is some failry shonky soldering, some of which I will probably redo. There is also a little rust on a 3-wire metal cased part with '433.920' marked on it; a SAW filter I assume? I guess this may have failed, but the LED on the bell push doesn't go on when you press the switch, and I think this is independant of the oscillator/transmitter. Oh, and yes I checked the batteries...

As I say, not a big deal, but I'd be interested if anyone knows of any common failure modes before I get in too deep...

Thanks (and a ding-dong New Year to you all!) Jon N

Reply to
jkn
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If it's what's known as a 'tactile' switch - usually with a square base and four mounting legs (or may be two) and sealed, they can and do fail. There are lots of variations, though - but they share one thing. Cheap to make. You can buy dozens for a quid on Ebay. But perhaps not the exact one you need.

Do a search on Tactile Switch on Ebay and see if anyone sells one identical to yours.

Reply to
Dave Plowman (News)

Check for (and clean) battery contacts - corrosion on the permanently live parts of outdoor electronics is quite common. Corrosion products caused by battery leakage can be amazingly good insulators too.

Reply to
Andrew Gabriel

I reckon if the switch is showing an on resistance of 50 ohms, it could be the problem. Especially if the LED doesn't light. Could be proved by shorting it out and seeing if the LED comes on.

Reply to
Dave Plowman (News)

That probably explains why my cheap wireless door chime is still fully functional even after 5 or more years. The only battery I've had to replace is the 3 x AA cell battery in the sounder unit I keep in my upstairs office (about 4 or 5 battery changes in total afaicr).

I'm using the wireless door bell as a repeater to our existing trembler bell mounted on the front door frame which is currently powered from a pack of 3 PP3s wired in series. I've wired the wireless sender to the trembler bell via a 12v zenner and small silicon diode so that when the outside bell push is operated it also powers the wireless sender.

The tiny 12v battery in the wireless bell push is only ever used if its own button is pressed to attract my attention, usually by the XYL when coming back home with a lot of shopping or, occasionally, to announce her departure if I'm in the office with the door closed.

Operating the wireless sender's own push button doesn't operate the front door trembler bell (which is handy for testing the wireless door bell since I can hear it if I leave the office door open for such testing).

The wireless bell push is never exposed to any extreme weather conditions that would normally apply in most installations and this seems to demonstrate the benefit of avoiding such environmental stresses.

If the problem turns out to be the push button switch (500 ohms on resistance?), a better solution might be to purchase an ordinary bell push as a replacement and wire it across the original switch contacts and relocate the wireless sender on the inside of the door frame where it can remain nice and dry.

Reply to
Johny B Good

The "environmental stresses" may not be weather related. Our wireless chimes need to be reset every few months after use by someone (usually a white van delivery driver) of the "harder I push the louder it rings" persuasion. It was more often until I supported the circuit board with rubber washers so it bends less easily.

Reply to
Robin

En el artículo , jkn escribió:

They can't cope with the UK weather. My solution was to fit the cheapo wireless bellpush inside, then drill through and put a decent Friedland one outside wired in parallel with the cheapo. Problem solved, and the batteries can be checked/changed in the dry and warm.

Reply to
Mike Tomlinson

A nice idea, but that would entail drilling through the wood or UPVC doorframe, which is what they wanted to avoid when they chose the wireless option.

Reply to
Graham.

Well, yes, but I was really trying to learn if there was a particular area that 'can't cope with the UK weather'. As others have mentioned it may well be t he pushbutton switch (the spec of similar switches seems to indicate an ON resistance of < 0.1 Ohm, so my measurement of 50 Ohm may well indicate a a problem there) but I was wondering about specific experience.

Your solution may well be the one I will end up with; I wonder what the Friedland wired bellpushes use for a switch, and why that copes better. I appreciate that the fact that they run on 12V or so, and with a larger current, indicates a different type of switch...

Jon N

Reply to
jkn

En el artículo , jkn escribió:

Just bare bent copper contacts, but they've been making them for years and they're in wide use, and seem to cope ok with our weather. Tried to google for a pic showing the contacts but couldn't find one.

The little switches in the cheapos are enclosed, which makes them trap moisture and corrode, presumably.

Reply to
Mike Tomlinson

I'm surprised that they are just copper - I'd expect them to be a bronze or brass to give them resilience and springyness.

Andrew

Reply to
Andrew Mawson

Interesting ... like Andrew Mawson I'd expect them to be something like phosphor-bronze or similar, but whatever... I will probably pick one up to take a look

Yes, that's a good point, thanks.

J^n

Reply to
jkn

Most choose the wireless option because it is easy. Then moan on and on about false rings, not being able to hear it, poor reliability etc.

Put my transformer fed bells in when I re-wired this house 40 years ago. Still working just fine.

Reply to
Dave Plowman (News)

with a wireless one you can take a receiver into the garden and still hear if there's someone at the door.

Reply to
charles

And then forget you've done it. ;-)

Reply to
Dave Plowman (News)

And nextdoor-but-one when feeding their cat while they're away - confuses delivery drivers no end which I consider a "good thing"

Reply to
Robin

Fair enough but the OP was considering a repair of the door bell sender so might view this as a possible solution. After all, it's only a matter of a metre or two of wiring, the sender still saves on running a wire to a remote bell.

Reply to
Johny B Good

The last time I looked at such a door bell switch, it was just a couple of brass strips pushed together by the button press. They had a decent airgap considering the low voltage and made a sliding/rubbing contact which bodes well for maintained low on resistance (or even the option for the operator to find 'The Sweet Spot' when age finally takes its toll on the switch - crude but effective).

Reply to
Johny B Good

I'm a +1 to removing the sender from outside. My experience was that it wa s the contact between the button cells that was the problem due to the weat her. I was fortunate in that I had cable already in place to put a decent push button switch, and put the original sender up in the attic where it ha s a wider range of transmission as well.

Rob

Reply to
robgraham

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