Very Very Small Flasher Curcuit 1

[dino40]

Good Day Everyone,
Once again I need Your suggestions I have been tasked with coming up with a solution and I would like to ask for your input. I need to make a Flasher Curcuit for a safety device the parameters are as follows:
1. Self contained 2. Flash about 4 times a second. 3. About the size of a stack of four nickels 4. Disposable.
I have the LEDs and battery but I need the switching portion any Suggestions? Thanks for your time Dino40

 

[MacGyverS2000]

Using a 555 timer is probably the easiest method here... if it's disposable, don't worry about current regulation, as the LED will mosre than likely last longer than the batteries will anyway.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

The obvious answer is the 555 timer chip or equivalent. Would also require a couple of resistor and a capacitor.

You'll sometimes see bare chips mounted to a tiny PCB card, wires bonded, and then covered with a blob of epoxy (musical greeting cards for example). Can be very tiny.

Once upon a time (maybe 12 years ago?), there was an 8-pin flasher chip. Radio Shack used to sell it. I assume it is long obsolete. Part Number LM3909.

You could also use a discrete transistor circuit a la Forrest M. Mims III (Radio Shack circuit cook books).

Oh, there are some LEDs with flasher circuits BUILT IN.

Lots-a-Links:

http://www.google.com/search?q=flasher+circuits

 

[nbucska]

Can U use flashing/blinking LED ?

Plesae read FAQ240-1032
WEB: <

http://geocities.com/nbucska/>

 

[IRstuff]

http://home.cogeco.ca/~rpaisley4/LM3909.html

TTFN

 

[dino40]

Thanks All,
I found a circuit with two switching transistors and a couple caps and resistors. I got it working quickly,now it's up to "the powers that be" if they want to use it.
Thanks to all for the input keep the component side up and the solder side down.

 

[VEBill]

Dan's comment, "...don't worry about current regulation..."

It reminds me of those tiny 'Dollar Store' Super-Bright LED keychain flashlights where the Super-Bright LED is simply shorted directly across two lithium button cells.

They work fine, but who'd have thought so?

 

[MacGyverS2000]

They work mostly because the voltage on the cells quickly drops below the typical forward voltage of the LEDs... for a short while it's above and the current flows heavily, but it settles down soon enough. Also, people rarely have those keychain lights on for longer than a handful of seconds, so by the time the LED die heats up, they've turned it off.

Yes, the LEDs do have a shorter lifespan than they could have, but for a keychain, do most care about the difference between 50-100k hours and 1-5k hours? Probably not. Still, it would kill me to ship a product designed in such a manner... the engineer in me would cringe. Some of my products have been working for years with no visible sign of output degredation, but I current-control the suckers and underdrive them.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[MikeHalloran]

The 555 requires external components, and costs more than a low-end PIC, which has been used to flash the LEDs in sneakers (also a disposable app).



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

I am totally with Mike here. Ditch that mess of parts. Get a PIC10F. One part. Any blink pattern or length of time. Controlled logical triggering. Cheap. Superior solution.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

Kinda forgot about those 3-pin PICs since I've never used them... good solution.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

3-pin PICs? I see 6, but no mention of 3.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=74

Just curious. Thanks.

 

[MacGyverS2000]

errrr... it's an SOT package. I'm so used to SOT-3 transistors, 3-pin was at the front of my brain. Shame on me, meant 6-pin. Either way, great product dying to be used for solving a wide range of problems.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

You only have a SOT23-03 for a brain?!?!

(Shame on me!) (but I couldn't resist)

Yes they make a ton of sense for these type projects. No one who jumps into these 555 projects ever thinks of the boundary conditions that come with them.

Death to 555s!! Long live the uuP! (and I started out in the company the invented the 555s) I have a 1/2 inch thick manual on the 555.


Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[IRstuff]

only "at the front of my brain" ;-)

TTFN

 

[VEBill]

At some outfits, the documentation overhead that comes with a 'Software Project' (even just a flashing LED) would bring a cost of ~many~ tens of thousands of dollars. And there's no escape clause for 'It's just a flashing LED!!'

You could probably purchase a truck load of hardware for the added NRE cost of a 'Software Project'.

YMMV.

 

[itsmoked]

Naw! You could probably get up to speed for under $200 and then have a useful ability to throw into your tool box instead of the same old limited confusing 555 junk. [blue]We are supposed to be talking Engineering here...[/blue] You could spend more than $200 in time screwing with dead-end 555's. And like I keep saying once you get the light blinking the first thing you want to do is change the pattern or the scheduling which either can't be done, or takes 5 times longer to figure out then the software project would have.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MikeHalloran]

I loved the 555, and used it for lots of cool stuff beyond flashing lights.

The PIC is actually much easier to get started on, and can do a whole lot more in a whole lot less space.

For flashing lights, you certainly don't need to write any code of your own; they've got app notes up the wazoo, covering every simple application you can think of, and some you wouldn't expect, and free tools that are actually pretty good.

I wouldn't even consider using "C" for this. It just adds power you won't use, and obfuscation you don't need. Step through some PIC assembly in the simulator, and you'll get it pretty quick.



Mike Halloran
Pembroke Pines, FL, USA

 

[VEBill]

Policies and Procedures. Not what necessarily needs to be done by common sense, but what MUST be done. Here's a typical list of the additional documentation required for any 'Software Project' (over and above the usual design package for a pure hardware project) at larger engineering companies:

Software Development Plan (SDP)
Software Test Plan (STP)
Software Installation Plan (SIP)
Software Requirements Specification (SRS)
Software Design Description (SDD)
Software Test Descriptionn (STD)
Software Test Report (STR)
Software Product Specification (SPS)
Software Version Description (SVD)
Software User Manual (SUM)
Software Input/Output Manual (SIOM)
Firmware Support Manual (FSM)
Version Description Document (VDD)

For a flashing LED, you might be able to 'tailor' (trim) the list a bit. But the effort to obtain authorization for tailoring would probably be significant. And there might be a whole raft of separate design review meetings just for the 'Software Project' part of the design.

And this is the pre-CMMI list. With CMMI at the higher levels, there would be more. Much more.

I ain't joking.

This probably explains why smaller companies sometimes can do things more cheaply than larger companies (not that there's anything wrong with that...).

 

[VEBill]

Related interesting link:

http://www.ti.com/ez430

"Complete...Development Tool in a USB Stick."

(Not directly applicable to the thread, but interesting just the same.)