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Hello, and my "Total Geekiness" entry

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Hello, and my "Total Geekiness" entry

Old 11-19-04, 12:32 AM
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Hi folks,

I've been commuting across the city here (in San Jose) for a while now, and lurking in the forums. Y'all have proven informative. Thanks a bunch for all of the tips.

I figured I'd write to say "hi", and share the geeking-up I've done to my commuter:

1) Headlights. I kicked around the idea of making my own, but when the Nite Hawk Dual Pro system came up for sale on Nashbar for $60-something (after coupons, before shipping), it was too good to pass up: the compact size, the pre-built switches, the quick releases, and the reasonably fast charger all come together to form a nice package. The system uses a 12V sealed lead acid battery which, while heavy, is at least user-friendly. I was looking at 12 SLA for any custom battery system I'd make, anyway. The bulbs are 12V MR11 halogens with 10 degree beam angles; one is 10W and the other 20W. The one I bought came with a helmet mount, along with an extra switch and wiring for it; I used that extra wiring to patch in my geek kit.

2) More lights! Using a 12V battery opened up the options here. I raided the trailer lighting section at West Marine, buying a bunch of low-profile sealed LED lights made by United Marine Inc. I picked up a taillight which has ten high-power red-orange emitters ("spider" LEDs?) in it, with lenses shaped into the clear plastic cover. This thing is bright, and pulls 2-3W on high. I also picked up three amber side-marker lights, each of which has two amber emitters, and mounted them near the front of my frame facing left, right, and forward. Each of these pulls about 0.6W. While not as fearsome as the taillight, they'll still leave spots in your eyes if you look straight at 'em in the dark. I put one on the front to help with visibility, and to give me at least some signature from the front if my halogens are out for whatever reason. The rear light is West Marine #5344692, while the others are West Marine #5344726.

3) Flasher. I wanted the amber lights to flash on and off to draw attention, and I wanted the tail light to alternate between high and low intensity both to draw attention and to save some power. I tried a couple of different flasher modules from auto parts stores (including a "light duty" motorcycle one), to no avail. To address this, I whipped up a simple circuit to flash them at about 3Hz; since I was making my own, I left an option to hook up a brake switch that forces the taillight to high while the others keep flashing. It's all solid state; I'm sure the clicking of an auto flasher would've driven me nuts anyway. I mounted the flasher circuit under my rear rack; it's pretty inconspicuous, being about the size of a matchbox. First, I encased it in epoxy for shock and weather resistance, and then I wrapped it in black tape to make it less noticable.

4) Battery monitor. Just to be a nerd, I decided I wanted some sort of battery discharge status indicator. I considered a couple of different approaches -- the coolest-looking of which would've been a 10-segment LED bar display, coupled with one of the ready-made driver chips National makes for them -- but I decided I wanted to keep it as inconspicuous as possible, instead of having a big indicator sticking up somewhere. I ended up making a small circuit which drives a single dual-color LED to indicate the discharge state: off for high, green to indicate low battery (meaning, 15-ish minutes remaining with 20W halogens and flashers, 25-ish for 10W + flashers), and red showing a battery critical condition (meaning, turn the battery off ASAP to avoid damage). I shaped the circuit board so that it'd fit in my fork/head tube, and mounted the sole LED where a brake lever and shifter meet. It's practically invisible when it's off. The idea is that I'll get some warning before my battery poops out, and I'll have the option of cutting the halogens and limping along on LEDs only for quite some time, if need be.

Attached are some shots of the bike with its spiffy geek lighting. One really must appreciate the duct-tape-and-zip-tie mounting system. It's tough to convey the effect of the lighting, since my point-and-shoot digicam fiddles with the light levels and colors, but one of the attachments shows the bike lighting from the front in an otherwise dark room. (All of that red light is from the rear monster reflecting!)

Stay safe,

-JAB
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Old 11-19-04, 12:46 AM
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For completeness, here are the circuits I ended up using. The flasher design is admittedly ham-fisted; I built it in a hurry.

The battery monitor is a bit nicer and power-conscious, but if I had it to do over again, I'd increase the hysteresis a bit (maybe drop those 4M resistors to 2M). I did the prototyping with the bike lights before I added D2/C1/C2, which effectively cuts the hysteresis enough the voltage swing from the flasher is enough to cause the indicator to flash between red and green a few times with the halogens on high. Oops. I'll say that's a feature, not a bug... yeah.

In addition to the obvious nightime usage, the flashers are great for helping me stay visible on misty mornings, going under bridges, etc. in the daytime.

-JAB
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Old 11-19-04, 04:41 AM
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That's pretty impressive, to say the least. You've put a lot more work into that than I would ever consider doing. I'd just buy a decent headlight and taillight and call it a day.
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Old 11-19-04, 05:58 AM
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wow that is cool- i wish I was so geeky and new about electronics
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Old 11-19-04, 12:21 PM
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Originally Posted by cryogenic
That's pretty impressive, to say the least. You've put a lot more work into that than I would ever consider doing. I'd just buy a decent headlight and taillight and call it a day.
That's pretty much what I did with the headlights, but one of the design goals I had was that the whole system be run from a single battery, with a convenient charging connection. That way, when I get home at night, it only takes me a second to connect the charger, and the whole system will be good to go for the next day. I didn't want to have to worry about multiple chargers, removing multiple cells to place them into chargers, or anything like that; I know my own laziness would lead to situations where I'd forget to charge some of them, or I'd play the game of extending the charge "just onnnne more day". Here, I put in a bit more one-time work up front, in order to reduce the amount of hassle incurred on every ride.

Beyond that, when I looked at pre-made tail lights, I didn't see any that I really liked; back then, they were all powered by AAA cells, which I don't particularly like. Cat Eye's new 2*AA tail light looks nice, though, I wouldn't be ashamed of that. My side/front marker lights are just bonus.
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Old 11-20-04, 02:50 AM
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This is awesome! I've grabbed the battery monitor circuit. Now I have to ask... I see you're working with a 12v system. Mine is 6v... what changes should I make? (I use circuits quite happily; re-engineering them is a completely different topic!)
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Old 11-20-04, 01:37 PM
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Originally Posted by Becca
I've grabbed the battery monitor circuit. Now I have to ask... I see you're working with a 12v system. Mine is 6v... what changes should I make?
The circuit works by comparing a fraction of the battery voltage, say 0.48 * (V_batt - V_D2) against the reference voltage, V_ref; the adjustment varies that multiplier smoothly from 0 to 1 in order to set the threshold, while V_D2 is roughly constant near 0.7V. There are two of these comparisons that take place with two different multipliers, one for each threshold.

For development, I heartily recommend breadboarding this until you get it working just as you want it, and using an adjustable-voltage power supply to test the behavior at different supply voltages. I just put an LM317T adjustable regulator on the breadboard with the circuit, along with a few resistors and a trimmer to vary the voltage.

So, hmm, let's see... First off, you'll definitely need a lower voltage diode for D1, which sets the reference voltage, and you may need to pick a lower value of R1 to go with it. The Zener voltage needs to be well below (V_batt - V_D2), so that enough current flows through R1 and D1 ((V_batt - V_D2 - Vz) / R1) that the voltage across D1 is stable, even as V_batt drops with battery use. How much current is needed will vary with the specific diode, but I'd look in the 1-20mA range for starters. I see that http://www.nteinc.com/Web_pgs/Half.html lists diodes with Zener voltages down to 2.4; I'd try to keep it below 3V, if possible. Radio Shack seems to only have Zeners at 5.1V and 12V, so you may have to find a real electronics store. You may also need/want to just eliminate D2; I added it for some measure of reverse polarity protection, since reverse current will fry that op-amp double quick. The 0.7V drop from D2 may end up squeezing you since it decreases your voltage quite a bit, whereas it didn't affect me much at 12V.

Next, you'll need to make sure that the op-amp you use can handle the lower supply voltages. I don't know offhand about the NTE889M that I used. By the way, the Rat Shack seems to have a comparable part, the National TL082 (rat shack part #276-1715).

You'll also need to lower R8 and R9, which limit the current through the LED; with the values I used, you may not get enough to usefully light it. Definitely keep an eye on the current through the LED, though, because op-amps typically can't source or sink that much current, and this circuit demands they do both. Instead of using a single 1k resistor on one of the outputs, I used two ~500ohm ones, that way each op-amp output would have some protection if the circuit output was shorted to the supply voltage or ground. I only put about 5mA through the LED. Bear in mind that besides worrying about the current limitations of the op-amp outputs, as the LED current increases, it also pulls the op-amp output voltages closer together, which can affect the operation of Q1.

What else... R2 and R3 aren't to sensitive to the values you use; they deal more with proportions. I'd keep the values above 20k or 50k, just to avoid needlessly wasting power in them. I used 100k because that's what Fry's happened to have in stock. However, I'd say to get some "precision" trimmers -- I used some 25-turn ones -- lest you drive yourself mad trying to set the thresholds. If you're stuck using 1-turn trimmers, then you should probably use large fixed resistors on either side of the trimmer to reduce the range over which it adjusts, to "zoom in" on the proportions, so to speak. I say, get some precision trimmers and avoid the hassle. The circuit may act weird if the thresholds are set weird; you may want to figure out the needed multipliers, and set the trimmers near them using an ohmeter before you get started in the circuit.

There's a good chance you'll also need to tweak the values of R6 and R7; they serve to divide the output voltage of the lower op-amp such that the base current of Q1 is high enough to saturate Q1 when the op-amp output is high, but not much more. Keep in mind that the op-amp output won't go completely to either 0v or the supply voltage, especially with the LED attached. (So calibrate R6/R7 with the LED in the circuit.) This isn't too hard to do, really; keep an eye on the voltage across Q1 (emitter-to-collector); when the battery is good, the voltage drop should be really small, less than 0.1V. When the battery voltage drops to critical, V_Q1CE should jump up to near the supply voltage. Using your adjustable voltage regulator, vary the supply voltage slowly across the thresholds, to ensure that you get a clean transition without the LED dimming as you cross them. The base voltage will be (V_U1_7 * R6/(R6+R7)), and it needs to stay pretty low. Be careful using an R7 lower than 1k or so, as you may cook Q1 or the op-amp. If R6 is too low, Q1 won't be able to turn "on", which will prevent the LED from turning from red to green; if R6 is too high, Q1 may not be able to turn off at one of the threshold crossings, keeping the LED from turning red. The LED may also go dim near the threshold crossings in these cases.

The values of C1 and C2 aren't too sensitive; they're mainly there to filter out any ringing. Without them, the circuit can oscillate; if this happens, you may see the LED dim or turn orange, as the red and green elements will alternate in rapid succession. Make sure they're not polarized capacitors.

Finally, there are the feedback resistors, R4 and R5. These need to be kept at high values. The higher they are, the less hysteresis you'll have at each threshold. The schematic has an approximate equation for the hysteresis at the bottom, which you can use as a guideline. The key thing is that the hysteresis voltage varies inversely with the feedback resistance. You don't want too much hysteresis, as it can cause the threshold voltages to overlap; also, if you have a large hysteresis, a short voltage drop out from hitting a bump or something can trigger a threshold, but then the voltage goes back up it may not be enough to reverse the change. I'd shoot for 0.1V-0.25V, unless you know more specifically what you want.

You'll have to decide on which threshold voltages to set. This depends on your battery, really. Since I've got a 12V sealed-lead-acid, VRLA if I recall correctly, I took the suggestion at batteryfaqs.org of never discharging below 10.5V, and set that as my "critical" threshold. Then, I made a voltage-versus-time plot of my light system discharging (attached), and set the "low" threshold based on the estimated run-time; 11.5V gives me about 25-30min with 10W halogens + flashers.

I hope this is clear enough... and I hope you've got a meter. If you have any more questions, feel free to ask. Oh, and here's a PDF copy of the circuit I used, it may be easier to read.
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Old 11-20-04, 01:52 PM
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Oh yeah, just for giggles: I mentioned in the "Total Geekiness" thread that my first charger from Nite Hawk didn't work right. After their great customer service guy (Mike H.) sent me a new one, I cracked open the old one, just to see what was inside. Here's what I found, in case anyone is curious.
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Old 11-21-04, 01:32 AM
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Thank you, Jab! I've printed off your post, and a copy of the PDF. It looks like fun!

Neat post about the innards of your charger. It's a bit more involved than my home-brew version that I have on my bike (see the "Total Geekiness" folder for all that.) It seems to be a bit... overkill.

Have you opened up the Nite Hawk's control box yet? Ever since I tied my bike's electrical system into the power connection for my NH, my headlight will occasionally extinguish if I hit my brake. I'm becoming amused and annoyed at the same time. I suspect I could enter that box (heck, I've already voided the warranty) and find a complex circuit there that could be ripped out, and a simple on/off toggle switch to replace the momentary NO switch they have now. Then no more trouble with the headlight turning itself off!
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Old 11-21-04, 02:10 PM
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Originally Posted by Becca
Neat post about the innards of your charger. ... It seems to be a bit... overkill.
The Nite Hawk charger is actually pretty simple as chargers go; it's just a two-stage charger. If the battery voltage starts below a given threshold, it runs in "high charge" mode; it maintains this until the battery reaches a threshold, at which point it switches to a simple float charge. The float charge mode maintains constant voltage. (The op-amp on the left determines which mode it's in; the one on the right just acts as an inverter.) They've got that 7812 voltage regulator (U2) hooked up in a weird sort of way, though.

The only way I could see to simplify it more would be to either make it a fixed-voltage float charger -- which would take a long time to charge, and may not use the battery to its full potential -- or by making it a trickle charger which must be removed after a certain number of hours. They've got a nice mix here: it charges up most of the way in <8 hours or so, but then switches to a float charge that can be maintained indefinitely. "Fire and forget."


Originally Posted by Becca
Have you opened up the Nite Hawk's control box yet?
My Nite Hawk ("Dual Pro") has no control box; the control system consists simply of plain-jane switches, with weatherproof rubber boots over them.


Originally Posted by Becca
Ever since I tied my bike's electrical system into the power connection for my NH, my headlight will occasionally extinguish if I hit my brake.
Out of curiosity, where did you tie into the system, and how much current does your brake system pull?

If they've got some fancy digital brightness control, it could be running at high frequencies, and it might be sensitive to additional load... particularly reactive loads.
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Old 11-21-04, 05:56 PM
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See? It's not about the bike, it's about the light!!
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Old 11-21-04, 06:21 PM
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Originally Posted by jab
The Nite Hawk charger is actually pretty simple as chargers go; it's just a two-stage charger.
The one on my bike has wires coming from my rim generator to a full wave bridge, then a 1000 micro-farad cap, and finally a 6v zener. That sends power to everything, including the battery. Now, *that's* simple!


Originally Posted by jab
Out of curiosity, where did you tie into the system, and how much current does your brake system pull?

If they've got some fancy digital brightness control, it could be running at high frequencies, and it might be sensitive to additional load... particularly reactive loads.
I tied into the NH cord just "North" of the battery and "South" of the cable split where one leads to the power switch and the other leads to the light. It's pretty simple right there with two wires. I put a connector there and just added my wiring to the "North" side of the connector.

As for my power... ummmmm... six LEDs at probably about 0.230 milliamps each, all in parallel with a 24 ohm resistor in series with all of them. If I remember my basic electronics, that should be about 0.725milliamps added into the circuit. That's the tail/brake lights. If I add in the turn signals, that's eight more LEDs flashing at a time, similar setup.
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Old 11-22-04, 01:57 AM
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Originally Posted by Becca
I tied into the NH cord just "North" of the battery and "South" of the cable split where one leads to the power switch and the other leads to the light. It's pretty simple right there with two wires. I put a connector there and just added my wiring to the "North" side of the connector.

...
Hmm, that sounds fine. I guess the first thing I'd check would be the connections, and the second would be to put an ammeter in series with your additional load, to verify that it's only pulling what you're expecting. You could also slap a voltmeter at the first junction "North" of the battery and watch the voltage there as you fiddle with things; if your extra load pulls it low enough, it may be triggering "low power, better shut off" electronics in the NH controller.

Regarding all of those LEDs in parallel, sharing a single current-limiting resistor, just a note: the forward voltage of LEDs can vary quite a bit between otherwise identical-looking units, especially the high-powered ones, and especially the white ones. So, the current division between the LEDs may not be as even as you'd expect; the high Vf units might be slacking around, while the low Vf units do the heavy lifting. (The forward voltage also varies with the internal temperature.) I think the Vf can also vary a bit over the life span of the LED, so when possible, folks recommend running them in series and using current instead of voltage regulation. (Though that might be overkill here.)

Best of luck with it,

JAB
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Old 11-27-04, 01:42 PM
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I spent a few minutes this morning twiddling with the circuit design, with an eye towards 6V operation.

First off, I changed D1 to a 3.6V Zener. I happened to use a 1W diode; as it turns out, the 1W parts take substantially more current to approach their Zener voltage than the 1/2W part I used in my 12V circuit (1/2W 5.1V NTE5010A's spec iZ = 20mA, 1W 5.1V NTE135A iZ = 49mA, 1W 3.6V NTE134A iZ = 69mA). Even with the 1/2W part, most of the overall circuit current draw is used for the Zener diode, so boosting it to accommodate a 1W part is even more wasteful. In order to accommodate the 1W diode, I dropped R1's value from 10k to 1k.

Here's a summary of the other changes: 1) Ditch D2; 2) R6 up from 10k to 22k; 3) R4 and R5 to 1Mohm (or lower, for more hysteresis); 4) R8+R9 dropped drastically. In my test circuit I eliminated R8 and R9 entirely, and the LED current draw was only a couple of mA... but that leaves the opamp outputs exposed and vulnerable to short circuits.

As far as the opamp U1 goes, I swapped out the NTE889M and tried the National TL082 (Rat Shack part 276-1715) to see how it worked. The TL082 pulled more current (about 4.5mA more in the 12V configuration) and didn't put out quite as much current for the LEDs.

When it came to setting the voltage thresholds, I just used 5.5V and 5.0V for testing. For a 6V SLA system, I'd probably just use 5.25V for "critical" and then set "low" based on my run-time; for a NiMH system, I guess I'd choose the "critical" voltage based on the number of cells, at 1.0 or 1.1V per cell.

Best of luck,

JAB
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Old 11-27-04, 08:53 PM
  #15  
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Nice work indeed. Question: do the brake cables get in the way of the headlight beams? I see you have the lights positioned under the bars. Looks clean though.

Have you considered alternate power sources? For example, Shimano used to make a hub with an internal generator that was extremely quiet and efficient...I'm not sure if they still make them, but I've seen a few for sale. It could probably support a 20W load (I forget exactly) You could add a small battery to stabilize the supply and keep the lights going while stopped. The advantage would be automatic charging and potentially lighter weight, as well as being pretty cool
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Old 11-27-04, 10:28 PM
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Originally Posted by enduro
do the brake cables get in the way of the headlight beams?
No; it took some fiddling, but I dressed the cables so that they're almost totally outside of the beams. The cables catch a teensy amount of side-spill, as does the front fender and tire, but it's not even enough to cast a noticable shadow in the beam. The centers are clean.

Originally Posted by enduro
Have you considered alternate power sources?
Not seriously. I wanted to minimize the amount of money I put into this cheaper bike, so I didn't want to shell out for new generator hubs or anything like that. After coupons and with a sale, the headlights were about $63 at Nashbar!

I thought that hub generators only put out about 3-5W? I really do like the idea of not having to worry much about batteries and chargers. While my lead-acid battery is very user-friendly as far as charging goes, it sure it heavy. Since this is a commuter and not for long-haul touring or anything, the weight and runtime aren't a problem. Still, now that I think about it, even a low-power generator would be nice to run the side and rear LEDs for safety lighting in the event of main battery exhaustion.

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Old 12-03-04, 07:41 PM
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Another good thread for DIY folks to bring back to the top!
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Old 12-13-04, 12:09 AM
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Soft start: the geekiness continues.

Not long after I geeked up my commuter with LEDs, I had my 10W halogen headlamp blow out when I powered it on with a fresh battery for the ride home. Shortly afterwards, my roomie's 10W halogen also blew at power-on with a fresh battery, which got me thinking: he bought the same headlights at the same time as I did, and we each got less than 100 hours of runtime out of them, far less than the 2000 hour average bulb life that bulb makers advertise.

I figured -- without any data to back it up -- that the stress of the sudden heating at power-on, particularly with the higher voltage of a fresh battery was shortening bulb life. So, I cooked up a "soft start" circuit which fades the light in over about one second, to go easy on the filament. A nicer solution would be to wire up some high-flux LEDs with optics to yield blowout-proof lighting, but this was quick and easy to do.

Here's the circuit; it's a simple three-wire job which sits in series on the ground leg of the light, past the power switch. I've prototyped it, testing with 10W, 20W, and 30W light loads on my 12V SLA battery, and it worked fine on all of these. I've also tested it down to 10.5V (with the 10W only; I'm lazy). I measured total overhead at 39/92/201mW for 10/20/30W loads, nearly all of which is heat dissipated in the power MOSFET, Q1.

This one may take a bit of tweaking (beyond just getting a lower-voltage D1) to adapt from 12V to 6V operation, due to the gate-to-source threshold of Q1 (up past 4V for a solid turn-on) being closer to the battery voltage, especially as the battery runs down. Depending specifically on the MOSFET used, it could work out, but I haven't really thought about it. One could eliminate the R1/D1 regulator, and make the timing circuit track the battery voltage (perhaps with a voltage divider), though that would lead to a slower turn-on at lower voltages.

I didn't actually build this circuit and put it on my old war horse, because my days of >10mi night-time urban commutes are almost over; I'm moving soon, but I figured I'd share.

Have fun,

JAB

Last edited by jab; 12-13-04 at 03:14 PM.
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Old 12-13-04, 12:16 AM
  #19  
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Oh, I almost forgot: I also made a 12V flasher circuit for my roomie's bike. It has a single flash output, and an input for a brake switch. It's a bit simpler than the one I made for my bike. If I had to do it over again (again), I'd probably use a CMOS timer and a MOSFET for switching (to use less power), but this one's not too greedy.

Stay lit,

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Old 12-13-04, 03:16 PM
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Soft start: the geekiness continues.
Ach! I just realized that I mis-drew the soft start diagram I initially posted, with D1 backwards. Fixed.

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Old 12-16-04, 11:17 PM
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Here's a chintzy way to adapt the 12V soft start circuit (v1.1) for 6V use.

There are more elegant ways to do this, but I was able to quickly hack the circuit to function in a 6V system, with a few parts I had on hand: I added an AA cell in series between R1 and the positive supply, and changed R1 to 4.7k. The battery raises the voltage "seen" by R1/D1 enough to keep the circuit pretty stable down to 4.5V or so on the main battery. The circuit draws very little current from the booster battery, less than 1mA in my test, so that battery will last a long, long time. With an AA or an AAA alkaline, it could last for years, depending on usage.

More elegant solutions would include, changing D1 to 4 or so volts, lowering R1 to keep it stable, and then adjusting R1/R3/C1 to set the appropriate turn-on timing. I don't happen to have an appropriate diode sitting around, though. (The big concern would be that Q1 might not stay all of the way "on" as the battery voltage drops, since its threshold voltage is so close to the supply voltage.) Another way would be to use a voltage doubler, though I haven't thought that through.

Seeing spots,

JAB
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Old 12-17-04, 01:37 AM
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I've printed out the circuit diagram and destructions, and plan to give this a try! Heck, I may even upgrade to a 12v system!
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