144 lines
6.7 KiB
Plaintext
144 lines
6.7 KiB
Plaintext
(TLJ V1.0)
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Greetings. I almost never document - I'm a C hacker :-)
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This archive consists of a bike-light project, a small,
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single-cell flasher, and assorted sample schematics that
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implement the LM3909 LED-flasher chip.
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Well, a few things about the LM3909 are in order. How about
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a few quotes from a 1982 National Semiconductor LINEAR book
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that I got (and can't live without):
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"The LM3909 is a monolithic oscillator specifically designed
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to flash Light Emitting Diodes (LEDs). By using the timing
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capacitor for voltage boost, it delivers pulses of 2 or more
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volts to the LED while operationg on a supply of 1.5V or
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less. The circuit is inherently self-starting, and requires
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addition of only a battery and capacitor to function as a
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LED flasher."
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"...will operate in the range -25C to +70C. It has been
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optimized for low power drain and operation from weak
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batteries so that continuous operation life exceeds that
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expected from battry rating." (nice touch)
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"Timing capacitors will generally be of the electrolytic
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type, and a small 3V rated part will be suitable for any
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LED flasher using a supply up to 6V. However, when picking
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flash rates, it should be remembered that some electrolytics
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have VERY broad capacitance tolerances, for example
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-20% to +100%."
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"Absolute Maximum Ratings:
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Power dissipation: 500 mW
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V+ Voltage: 6.4 V
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Operating Temp: -25C to +70C"
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End of quoting...
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The diagram found in the upper-right position in file
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L_SCHM1.GIF is as basic as one can get: cap, LED, LM3909,
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and a 1.5V battery. This is battery life for that circuit:
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+--------------+----------------------------------------+
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| Size Cell | Type |
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+ |----------------+-----------------------+
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| | Standard | Alkaline |
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+--------------+----------------+-----------------------+
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| AA | 3 months | 6 months |
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| C | 7 months | 15 months |
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| D | 1.3 years | 2.6 years |
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+--------------+----------------+-----------------------+
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With this in mind, the file D_CELL.GIF presents a small
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flasher that can be soldered and glued to a D-cell. I have
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one of these and use it when I got for walks in the park
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in the evening... (bonus: acts as a beacon for the thugs :-)
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For more charts, see file 3909SPEC.GIF. You'll find a chart
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of what capacitance gives what rate, etc.
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Lets see... Ok, now for the bike-light file CASE.GIF.
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Parts you will need:
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1) RatShack case Part # 270-220 or any other small plastic
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case. If you want to use it for exterior (is. can get
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rained on) applications, make sure it's water-tight or
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can be sealed easily with silicone rubber.
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2) Minature Toggle ON-OFF Switch (or can be also a push
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ON-OFF type). Basicly, ask yourself: "Will this run ALL
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the time or only when I need it?" If it's a marker or
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a gadget that will run off a car's electical system, you
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may not need a switch. If it's a flasher for a bicicly,
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definitely invest in a small switch. Get the LOWEST
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rated switch you can (Don't have RatShack # for this)
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3) Battery holder. If this is for a bike, you want to make
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it as shock-proof as possible. It's best if you can
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glue the holder inside the project case. If you can't
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find one that has a flat back, you can use the one that
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has the batteries on the sides - and just use a small
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piece of foam to keep it from moving. Using the chart
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above (battery life) pick the batteries & holder to best
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suit your application.
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4) High-Brightness LED. You CAN NOT use standard 1mcd LEDs
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as they are almost invisible from any distance. I used
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RatShack's Part # 276-087. Please see file LED_SPEC.GIF
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for more info. DO NOT buy the 5000mcd LEDs from RatShack.
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They are merely the 2000mcd in a bigger, better focused
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package (tell me if I'm wrong). Besides, it lists for
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$4.99 and you can get three 2000mcd ones for that price
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($1.68 a pop) The only other place selling something
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similar (I think) is Hosefelt. They have a "T-1-3/4
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High Intensity Bright Red" Part # UHO and lists for $.15
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If anyone knows other sellers of compareable LEDs, please
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let me know. (I just HATE it when mags, MCM and Hosefelt
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included, don't list brightness for LEDs!)
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5) LM3909. Yup, RatShack has it, Part #276-1705 and lists for
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$1.69 (not bad). MCM has it for $5.04 ("Earth to MCM..." :-)
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Lets see, it also cross-refs to an ECG-876 (no idea on price)
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Anyone know of a cheaper source? Outside USA?
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6) Capacitor. If you need low frequency (<500Hz) it has
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to be an electrolytic. If you want high freq, a tantalum
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or other can be used (note that .30 uF gives 1.1kHz)
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As the quote said, a 3V will do but use any voltage
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you can get. I used a sub-minature 400uF 6V part in my
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bike-light (to get 1.5-2Hz) A small hint: get a bunch
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of caps and plug-and-play. Pick the frequency you feel
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happy with :-)
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7) Perf-board. You don't really need one! It was just handy
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for me to attach the LM3909 to it and I also used it to
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keep the potting compound from leaking into the battery
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compartment. Cut it to fit snugly as shown in file CASE.GIF.
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8) Potting compound. You can use wax... if you live in cold
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climate :-) Epoxy is both expensive and also (for me)
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shrinks when it cures - breaking wires, etc. Besides, it's
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VERY permanent (as I found the... er... hard way - I could
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even SEE through the clear epoxy where the problem was :-(
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I found that packing "peanuts" work just fine.
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9) Wire. We're not talking amps - I used wire-wrapping wire.
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Don't use more than 18 gauge... unless you're one of the
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clowns that claims to "hear" the difference between normal
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and oxygen-free speaker cable ;-)
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10) Batteries. Obviously, the ones that fit the battery holder!
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This is not the time to be cheap - use alkaline! The don't
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leak as "much" (you mean they don't "never" leak? Yeah right)
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and they last almost twice as long (plus, they have a long
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shelf life...
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Well, that's about it. Oh, almost forgot, you better know what
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solder and flux and, most important, patience are applied. More
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assembly instructions are listed in the file CASE.GIF.
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By the way, I cheated and used the schematic that appears
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in the upper-right position in the file L_SCHM2.GIF - yes,
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the one for an incandescent... I found that it give VERY
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bright flashes for the 2 LEDs that I used (see CASE.GIF).
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Well, that's about it. If you have questions or comments or
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bug-fixes (ahmm) please e-mail them to "fmgst+@pitt.edu"
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of that bounces (??) send it to "fmg@alpha.smi.med.pitt.edu"
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Have fun, don't burn yourself with the iron, and don't inhale!
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