\t\t\t \t (TLJ V1.0)<\/p>\n
\tGreetings. I almost never document – I’m a C hacker \ud83d\ude42<\/p>\n
\tThis archive consists of a bike-light project, a small,
\n\tsingle-cell flasher, and assorted sample schematics that
\n\timplement the LM3909 LED-flasher chip.<\/p>\n
\tWell, a few things about the LM3909 are in order. How about
\n\ta few quotes from a 1982 National Semiconductor LINEAR book
\n\tthat I got (and can’t live without):<\/p>\n
\t“The LM3909 is a monolithic oscillator specifically designed
\n\tto flash Light Emitting Diodes (LEDs). By using the timing
\n\tcapacitor for voltage boost, it delivers pulses of 2 or more
\n\tvolts to the LED while operationg on a supply of 1.5V or
\n\tless. The circuit is inherently self-starting, and requires
\n\taddition of only a battery and capacitor to function as a
\n\tLED flasher.”<\/p>\n
\t“…will operate in the range -25C to +70C. It has been
\n\toptimized for low power drain and operation from weak
\n\tbatteries so that continuous operation life exceeds that
\n\texpected from battry rating.” (nice touch)<\/p>\n
\t“Timing capacitors will generally be of the electrolytic
\n\ttype, and a small 3V rated part will be suitable for any
\n\tLED flasher using a supply up to 6V. However, when picking
\n\tflash rates, it should be remembered that some electrolytics
\n\thave VERY broad capacitance tolerances, for example
\n\t-20% to +100%.”<\/p>\n
\t“Absolute Maximum Ratings:
\n\t Power dissipation:\t\t500 mW
\n\t V+ Voltage:\t\t\t6.4 V
\n\t Operating Temp: \t -25C to +70C”<\/p>\n
\tEnd of quoting…<\/p>\n
\tThe diagram found in the upper-right position in file
\n\tL_SCHM1.GIF is as basic as one can get: cap, LED, LM3909,
\n\tand a 1.5V battery. This is battery life for that circuit:<\/p>\n
\t+————–+—————————————-+
\n\t| Size Cell | Type |
\n\t+ |—————-+———————–+
\n\t| | Standard | Alkaline |
\n\t+————–+—————-+———————–+
\n\t| AA | 3 months | 6 months |
\n\t| C | 7 months | 15 months |
\n\t| D | 1.3 years | 2.6 years |
\n\t+————–+—————-+———————–+<\/p>\n
\tWith this in mind, the file D_CELL.GIF presents a small
\n\tflasher that can be soldered and glued to a D-cell. I have
\n\tone of these and use it when I got for walks in the park
\n\tin the evening… (bonus: acts as a beacon for the thugs \ud83d\ude42<\/p>\n
\tFor more charts, see file 3909SPEC.GIF. You’ll find a chart
\n\tof what capacitance gives what rate, etc.<\/p>\n
\tLets see… Ok, now for the bike-light file CASE.GIF.<\/p>\n
\tParts you will need:<\/p>\n
\t1) RatShack case Part # 270-220 or any other small plastic
\n\t case. If you want to use it for exterior (is. can get
\n\t rained on) applications, make sure it’s water-tight or
\n\t can be sealed easily with silicone rubber.
\n\t2) Minature Toggle ON-OFF Switch (or can be also a push
\n\t ON-OFF type). Basicly, ask yourself: “Will this run ALL
\n\t the time or only when I need it?” If it’s a marker or
\n\t a gadget that will run off a car’s electical system, you
\n\t may not need a switch. If it’s a flasher for a bicicly,
\n\t definitely invest in a small switch. Get the LOWEST
\n\t rated switch you can (Don’t have RatShack # for this)
\n\t3) Battery holder. If this is for a bike, you want to make
\n\t it as shock-proof as possible. It’s best if you can
\n\t glue the holder inside the project case. If you can’t
\n\t find one that has a flat back, you can use the one that
\n\t has the batteries on the sides – and just use a small
\n\t piece of foam to keep it from moving. Using the chart
\n\t above (battery life) pick the batteries & holder to best
\n\t suit your application.
\n\t4) High-Brightness LED. You CAN NOT use standard 1mcd LEDs
\n\t as they are almost invisible from any distance. I used
\n\t RatShack’s Part # 276-087. Please see file LED_SPEC.GIF
\n\t for more info. DO NOT buy the 5000mcd LEDs from RatShack.
\n\t They are merely the 2000mcd in a bigger, better focused
\n\t package (tell me if I’m wrong). Besides, it lists for
\n\t $4.99 and you can get three 2000mcd ones for that price
\n\t ($1.68 a pop) The only other place selling something
\n\t similar (I think) is Hosefelt. They have a “T-1-3\/4
\n\t High Intensity Bright Red” Part # UHO and lists for $.15
\n\t If anyone knows other sellers of compareable LEDs, please
\n\t let me know. (I just HATE it when mags, MCM and Hosefelt
\n\t included, don’t list brightness for LEDs!)
\n\t5) LM3909. Yup, RatShack has it, Part #276-1705 and lists for
\n\t $1.69 (not bad). MCM has it for $5.04 (“Earth to MCM…” \ud83d\ude42
\n\t Lets see, it also cross-refs to an ECG-876 (no idea on price)
\n\t Anyone know of a cheaper source? Outside USA?
\n\t6) Capacitor. If you need low frequency (<500Hz) it has
\n\t to be an electrolytic. If you want high freq, a tantalum
\n\t or other can be used (note that .30 uF gives 1.1kHz)
\n\t As the quote said, a 3V will do but use any voltage
\n\t you can get. I used a sub-minature 400uF 6V part in my
\n\t bike-light (to get 1.5-2Hz) A small hint: get a bunch
\n\t of caps and plug-and-play. Pick the frequency you feel
\n\t happy with \ud83d\ude42
\n\t7) Perf-board. You don't really need one! It was just handy
\n\t for me to attach the LM3909 to it and I also used it to
\n\t keep the potting compound from leaking into the battery
\n\t compartment. Cut it to fit snugly as shown in file CASE.GIF.
\n\t8) Potting compound. You can use wax… if you live in cold
\n\t climate \ud83d\ude42 Epoxy is both expensive and also (for me)
\n\t shrinks when it cures – breaking wires, etc. Besides, it's
\n\t VERY permanent (as I found the… er… hard way – I could
\n\t even SEE through the clear epoxy where the problem was \ud83d\ude41
\n\t I found that packing "peanuts" work just fine.
\n\t9) Wire. We're not talking amps – I used wire-wrapping wire.
\n\t Don't use more than 18 gauge… unless you're one of the
\n\t clowns that claims to "hear" the difference between normal
\n\t and oxygen-free speaker cable \ud83d\ude09
\n 10) Batteries. Obviously, the ones that fit the battery holder!
\n\t This is not the time to be cheap – use alkaline! The don't
\n\t leak as "much" (you mean they don't "never" leak? Yeah right)
\n\t and they last almost twice as long (plus, they have a long
\n\t shelf life… <\/p>\n
\tWell, that's about it. Oh, almost forgot, you better know what
\n\tsolder and flux and, most important, patience are applied. More
\n\tassembly instructions are listed in the file CASE.GIF.<\/p>\n
\tBy the way, I cheated and used the schematic that appears
\n\tin the upper-right position in the file L_SCHM2.GIF – yes,
\n\tthe one for an incandescent… I found that it give VERY
\n\tbright flashes for the 2 LEDs that I used (see CASE.GIF).<\/p>\n
\tWell, that's about it. If you have questions or comments or
\n\tbug-fixes (ahmm) please e-mail them to "fmgst+@pitt.edu"
\n\tof that bounces (??) send it to "fmg@alpha.smi.med.pitt.edu"<\/p>\n
\tHave fun, don't burn yourself with the iron, and don't inhale!<\/p>\n
