Hi Everyone,

I've created an engagement ring box and created a (VERY) simple tiny circuit which lights up 2 Pink LED's (pictured in capture1.jpg) with 2 LR44 Batteries

The circuit will keep the LED's on for around 35 hours before the battery dies.

I will be putting this circuit into an area of the box that will be covered by foam/ring so it will not be easy to get at so adding a physical switch is not possible (also room is VERY tight).

The first thing I thought of is those Flashing (Strobing) bouncy balls that have LED's that light up when the ball impacts. So I took one apart (pictured in capture3.jpg). The circuit seems mostly straight forward (the trigger is a small spring (coil) that when touching the circuit board completes the circuit and triggers the LED's to flash back and forth Red and Blue for around 15 seconds.

What I can't tell as there appears to be a hardened polymer around the timer part of the circuit as well as the LED's is what exactly they are using for the "timer" portion of the circuit.

Ideally I would like to be able to lightly tap or shake the ring box to have the light turn on for 2-5 minutes (minimum 2 minutes, maximum 10 minutes). I do not want the LED's to strobe and they should both stay on the entire time. I've done a lot of reading about 555 circuits and seen some similar topics here that reference monostable 555 circuits. I bought some 555 switches but they are fairly large and space is a major concern (and I'm not even sure if 2 LR44 batteries are going to have enough voltage to trigger a 555 switch.

So the question ---

What would everyone recommend I look into, is creating a tiny micro switch like this possible? Should I continue looking into a 555 (Maybe finding a smaller variant)?

Any help will be appreciated thank you.


-John

 

Here is a 2 volt 555 chip sized at 3mm by 4.4mm and one place you might buy it:
http://www.mouser.com/search/Refine.aspx?N=7655680&Ns=Pricing|0

 

Here is a 2 volt 555 chip sized at 3mm by 4.4mm and one place you might buy it:
http://www.mouser.com/search/Refine.aspx?N=7655680&Ns=Pricing|0

The datasheet you link to says minimum 4.5V operation.
The LMC555 would do better - down to 1.5V with 50mA output, SOIC 4.9mm x 3.9mm.

 

The datasheet you link to says minimum 4.5V operation.

You're right. I thought I had found the LMC555 in a different package (smaller).

 

How about this one @ 5mm x 6.2mm?
http://www.mouser.com/Semiconductor...ries/_/N-6j749?P=1yxz1ggZ1ypzff7&Ns=Pricing|0

 

There micro tilt & acceleration switches. I have some of the tilt switches, 4.6 mm dia. 4.8 mm tall. Source unknown. Can be used NO or NC to trigger a 555.
The C555 V supply 2 to 18V, but can only supply 10 mA - high V & ground 100 mA.
Should be the same as 7555; mine came from Radio Shack.

 

You might 'bodge' a tap switch by using a wire link held loosely on the PCB by kinking the wire and not soldered. It will make an intermittent contact when tapped.

 

can only supply 10 mA - high V & ground 100 mA.

It is simple enough to use the sink function with (2) LEDs.
The micro-tilt switch is a good idea, but some copper foil on the edge of the lid can be a switch, too.

 

There are also very small double pole reed switches used with small magnet.
Found a tilt switch same size @ Electronic Goldmine, G21036, US $ 1.99, $10.00 min. purchase.

 

Not ideal, but if you really have to you could use a tiny SMD comparator in combination with a long time constant of a RC circuit to hold the lights on until the capacitor reached a certain threshold voltage. This wouldn't solve the problem of triggering said circuit, but I believe some brilliant ideas explaining how to do just that have been mentioned above.

 

How about this one @ 5mm x 6.2mm?
http://www.mouser.com/Semiconductor...ries/_/N-6j749?P=1yxz1ggZ1ypzff7&Ns=Pricing|0

Thanks -- I suppose first step is "build the circuit with the 555's I already bought and then shrink it down by buying smaller parts where possible.

There are also very small double pole reed switches used with small magnet.
Found a tilt switch same size @ Electronic Goldmine, G21036, US $ 1.99, $10.00 min. purchase.

I actually attempted this first (a great idea!) I'm using 2 magnets flush in the top of the LID to hold the LID to the base and was hoping to find an extremely sensitive NC switch where when I pulled the magnets away the switch would close and light up. I bought about 3 different reed switches with the lowest AT values from mouser and none of them were sensitive enough to trip the circuit from how far away the reed switch will end up being from the magnets.
This idea would be ideal if only I could find a reed switch as sensitive as I need.
I've never used this website "Electronic Goldmine", it looks like they have more/different reed switches than mouser-- I'll have to take a look.

Thanks!



Thanks everyone for the comments and advice- I'll spend some more time messing around with 555 timers and possibly reed switches.

 

suppose first step is "build the circuit with the 555's

I spent most of an hour trying to figure a way to do this with a j-fet, but it always comes out using more bulk that the 555 IC.

 

Down the road if you are planning to mass produce these things you may want to think about a uC (Micro-Controller). Then take it further using a "black blob" or "blob chip" which if you get enough can be had very inexpensive. You have a wire bonded chip of silicon under a blob of an epoxy resin. You could likely start with a simple PICAXE 08M2 to practice with. I am only presenting the PICAXE as a starter example any of a dozen other chips could be used and next to no external parts are needed other than the trigger switch and battery supply. Once you code it then consider the blob approach.

Ron

 

The way I heard it was, "blob-top".
But yeah, I guess you could sell these by the tens of thousands to jewelry companies.
Just...every poacher in Asia would be making a hundred variations like heart shapes, and beating you to the door with a lower price.

 

The way I heard it was, "blob-top".
But yeah, I guess you could sell these by the tens of thousands to jewelry companies.
Just...every poacher in Asia would be making a hundred variations like heart shapes, and beating you to the door with a lower price.

Good point, maybe once you have a working design just contract them out to China. I have heard all sorts of names for that stuff, I guess blob top works as well as the next.

Ron

 

If one of the reed switches from Mouser is KSK-1C90U-1015, then it might be hard to find a more sensitive
form C switch as I checked many from Digi-Key with no better sensitivity than 10- 15 AT. They do have several varieties of ICM7555