momentry on/off with a reed switch

[oldzed]

Hi All
Have been following this forum for a while now and thought I would register and say hello.
I have started a few Maglight mods. The only thing I was not keen on was needing to ensure that my reed switch was always closed.

I bought a Pololu Pushbutton Power Switch SV. from these people
http://www.pololu.com/catalog/product/750
It lets me use a reed switch as a momentry on/off.
works very well with 7.4v, though it stayed on a few times when my li-ions were hot of the charger. when the voltage dropped a little it returned to working fine.

Thought I would just share it in case it is useful for anyone else

 

[gav6280]

Anyone know if this little circuit would be any good if the push switvh was replaced by a piezo? As i would like to use one of these:

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0226104

 

[SUBjohan]

Anyone know if this little circuit would be any good if the push switvh was replaced by a piezo? As i would like to use one of these:

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0226104

Would a piezo work under water?? What I mean is would the water pressure not activate the switch randomly??

Greetz Johan

 

[sucnip]

Yes, Piezo switches work quite well underwater. The switch closes (connects the contacts) for a duration proportional to the pressure exerted on the switch. For example, a hard press will cause a 0.5 second "press" on the button while a light press will cause a 0.1 second "press".

Piezo switches must be used with a logic level "flip-flop" circuit, microcontroller or other means of reading the pulses generated by the switch. They do not work in a conventional push on / push off way.

David

 

[gav6280]

Piezo switches must be used with a logic level "flip-flop" circuit, microcontroller or other means of reading the pulses generated by the switch. They do not work in a conventional push on / push off way.

So is that not what this circuit : http://www.pololu.com/catalog/product/750 listed in the OP doing?

 

[b-bassett]

from the looks of the circuit it should work with a piezo switch.

otherwise it can be done with a 555 timer, a transistor and a few resistors, worked ok for me but there is a 0.7 V drop over the transistor, when powerd up.

the circuit diagram was on here somewhere but i cant find it, ill see if i can find a link later.

 

[ufling]

It lets me use a reed switch as a momentry on/off.
works very well with 7.4v, though it stayed on a few times when my li-ions were hot of the charger. when the voltage dropped a little it returned to working fine.

Hi
Does this mean it can turn on and off a light using only one momentry "on" switch (reed or PIEZO)
Thanks
Uffe "UFLING"

 

[Klem]

Yes, a momentary switch like a Schurter piezo works fine underwater when attached to a momentary latching circuit.

I've used them in several dive torches.

The toggle circuit in this torch works with a reed switch...swipe a magnet onto the torch for ON, swipe again for OFF;
http://groups.yahoo.com/group/hiddivelights/photos/album/1481309361/pic/list

In this torch it's the piezo switch doing the same thing; press ON, next press OFF;
http://groups.yahoo.com/group/hiddivelights/photos/album/269274600/pic/list

The Pololu circuit looks like a more compact version of the same.

Klem

 

[gav6280]

Great thanks.

Im going for http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0226104 with http://www.pololu.com/catalog/product/750

 

[jspeybro]

Let us know how it works out with the Piezo. I'm interested

 

[lucca brassi]

In the catalogue of APEM piezo switches are more types depends from code (looks all the same ) http://www.apem.com/pdf/switch-pushbutton-PBA-ENG.pdf

- ''latch'' switches (on/off) - don't need ''hold circuit'' and need power section (FET, relay)
- push (momentary)button switch need both ''hold circuit'' and power section (FET, relay)


personaly: simple as bean
magnet , hall switch , FET, resistor , (led for fancy look)

 

[Klem]

Guys,

I've just tried two of those Polulu toggle switching circuits and they turned out to be a big disappointment.

Using a piezo as the momentary switch they go on, but will not switch off. You have to literally break the circuit.

I thought this might be either noise from the HID and LED circuits I used, or bounce/interference from the piezo....so I replaced both. I tried it with a trusty old 12V 35W incandescent globe and removed the piezo to just touching the switch wires together simulating a momentary switch. Same problem.

With 7.2V Li-ion touching wires works...it goes on, and off (but not every time).
With 11.1V touching wires goes on, but not off.

With a piezo, both 7.2V and 11.1V goes on, but not off.

There is a special 'OFF' contact on the PCB. They advertise this as a mechanism for protecting batteries from deep discharge. It does work, switching off by introducing a voltage. You could use this as the OFF but you would then need two momentary switches on your torch; one for on, and one for off (or a second switch to break the circuit).

Two switches on a torch starts to get unworkable so I think I'll stick to building toggle circuits out of 556timers and FETs...a tedious hour or so with a soldering iron!

BTW, I tried email the Polulu people for help but got some wierd guy who was less interested in fixing it than nursing his inflated fragile ego. He tried deflecting responsibility by suggesting it was a, "coincidence." I'll leave it for you to fill in the exlpletive.

My advice...J.U.N.K!!!!!!!