			 	                       (TLJ V1.0)

	Greetings. I almost never document - I'm a C hacker :-)

	This archive consists of a bike-light project, a small,
	single-cell flasher, and assorted sample schematics that
	implement the LM3909 LED-flasher chip.

	Well, a few things about the LM3909 are in order. How about
	a few quotes from a 1982 National Semiconductor LINEAR book 
	that I got (and can't live without):

	"The LM3909 is a monolithic oscillator specifically designed
	to flash Light Emitting Diodes (LEDs). By using the timing
	capacitor for voltage boost, it delivers pulses of 2 or more
	volts to the LED while operationg on a supply of 1.5V or
	less. The circuit is inherently self-starting, and requires
	addition of only a battery and capacitor to function as a
	LED flasher."

	"...will operate in the range -25C to +70C. It has been
	optimized for low power drain and operation from weak
	batteries so that continuous operation life exceeds that
	expected from battry rating." (nice touch)

	"Timing capacitors will generally be of the electrolytic
	type, and a small 3V rated part will be suitable for any
	LED flasher using a supply up to 6V. However, when picking
	flash rates, it should be remembered that some electrolytics
	have VERY broad capacitance tolerances, for example
	-20% to +100%."

	"Absolute Maximum Ratings:
	 Power dissipation:		500 mW
	 V+ Voltage:			6.4 V
	 Operating Temp:  	 -25C to +70C"

	End of quoting...

	The diagram found in the upper-right position in file 
	L_SCHM1.GIF is as basic as one can get: cap, LED, LM3909,
	and a 1.5V battery. This is battery life for that circuit:

	+--------------+----------------------------------------+
	| Size Cell    |              Type                      |
	+              |----------------+-----------------------+
	|              |  Standard      |  Alkaline             |
	+--------------+----------------+-----------------------+
	|     AA       |  3 months      |  6 months             |
	|     C        |  7 months      |  15 months            |
	|     D        |  1.3 years     |  2.6 years            |
	+--------------+----------------+-----------------------+

	With this in mind, the file D_CELL.GIF presents a small
	flasher that can be soldered and glued to a D-cell. I have
	one of these and use it when I got for walks in the park
	in the evening... (bonus: acts as a beacon for the thugs :-)

	For more charts, see file 3909SPEC.GIF. You'll find a chart
	of what capacitance gives what rate, etc.

	Lets see... Ok, now for the bike-light file CASE.GIF.

	Parts you will need:

	1) RatShack case Part # 270-220 or any other small plastic
	   case. If you want to use it for exterior (is. can get
	   rained on) applications, make sure it's water-tight or
	   can be sealed easily with silicone rubber.
	2) Minature Toggle ON-OFF Switch (or can be also a push
	   ON-OFF type). Basicly, ask yourself: "Will this run ALL
	   the time or only when I need it?" If it's a marker or
	   a gadget that will run off a car's electical system, you
	   may not need a switch. If it's a flasher for a bicicly,
	   definitely invest in a small switch. Get the LOWEST 
	   rated switch you can (Don't have RatShack # for this)
	3) Battery holder. If this is for a bike, you want to make
	   it as shock-proof as possible. It's best if you can
	   glue the holder inside the project case. If you can't
	   find one that has a flat back, you can use the one that
	   has the batteries on the sides - and just use a small
	   piece of foam to keep it from moving. Using the chart
	   above (battery life) pick the batteries & holder to best
	   suit your application.
	4) High-Brightness LED. You CAN NOT use standard 1mcd LEDs
	   as they are almost invisible from any distance. I used
	   RatShack's Part # 276-087. Please see file LED_SPEC.GIF
	   for more info. DO NOT buy the 5000mcd LEDs from RatShack.
	   They are merely the 2000mcd in a bigger, better focused
	   package (tell me if I'm wrong). Besides, it lists for
	   $4.99 and you can get three 2000mcd ones for that price 
	   ($1.68 a pop) The only other place selling something
	   similar (I think) is Hosefelt. They have a "T-1-3/4
	   High Intensity Bright Red" Part # UHO and lists for $.15
	   If anyone knows other sellers of compareable LEDs, please 
	   let me know. (I just HATE it when mags, MCM and Hosefelt
	   included, don't list brightness for LEDs!)
	5) LM3909. Yup, RatShack has it, Part #276-1705 and lists for
	   $1.69 (not bad). MCM has it for $5.04 ("Earth to MCM..." :-) 
	   Lets see, it also cross-refs to an ECG-876 (no idea on price) 
	   Anyone know of a cheaper source? Outside USA?
	6) Capacitor. If you need low frequency (<500Hz) it has
	   to be an electrolytic. If you want high freq, a tantalum
	   or other can be used (note that .30 uF gives 1.1kHz)
	   As the quote said, a 3V will do but use any voltage
	   you can get. I used a sub-minature 400uF 6V part in my
	   bike-light (to get 1.5-2Hz) A small hint: get a bunch
	   of caps and plug-and-play. Pick the frequency you feel
	   happy with :-)
	7) Perf-board. You don't really need one! It was just handy
	   for me to attach the LM3909 to it and I also used it to
	   keep the potting compound from leaking into the battery 
	   compartment. Cut it to fit snugly as shown in file CASE.GIF. 
	8) Potting compound. You can use wax... if you live in cold
	   climate :-) Epoxy is both expensive and also (for me)
	   shrinks when it cures - breaking wires, etc. Besides, it's
	   VERY permanent (as I found the... er... hard way - I could 
	   even SEE through the clear epoxy where the problem was :-(
	   I found that packing "peanuts" work just fine.
	9) Wire. We're not talking amps - I used wire-wrapping wire.
	   Don't use more than 18 gauge... unless you're one of the 
	   clowns that claims to "hear" the difference between normal
	   and oxygen-free speaker cable ;-)
       10) Batteries. Obviously, the ones that fit the battery holder!
	   This is not the time to be cheap - use alkaline! The don't
	   leak as "much" (you mean they don't "never" leak? Yeah right)
	   and they last almost twice as long (plus, they have a long
	   shelf life... 
	
	Well, that's about it. Oh, almost forgot, you better know what
	solder and flux and, most important, patience are applied. More
	assembly instructions are listed in the file CASE.GIF.

	By the way, I cheated and used the schematic that appears
	in the upper-right position in the file L_SCHM2.GIF - yes,
	the one for an incandescent... I found that it give VERY
	bright flashes for the 2 LEDs that I used (see CASE.GIF).

	Well, that's about it. If you have questions or comments or
	bug-fixes (ahmm) please e-mail them to "fmgst+@pitt.edu"
	of that bounces (??) send it to "fmg@alpha.smi.med.pitt.edu"

	Have fun, don't burn yourself with the iron, and don't inhale!
