low cost challenge

I have a bike light, with a single push button momentary switch. It toggles from off to high beam to low beam to strobe, then off.

I figure the design spec is purely manufacturing cost; no performance, precision, etc.

What's the solution? Notice that it has 4 states, which implies some kind of memory. IC, or discrete parts? Considering device and assembly costs. And an oscillator, and lamp driver.

Powered by two AA batteries.

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Rich
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RichD
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The cheapest solution that would produce an actual decent performance lamp would be an ASIC produced in quantities of ten million.

In smaller quantities but still in the thousands there are some one time programmable logic mixed-signal ICs that can probably pull it off for like 20 cents each in that quantity

barring that cheapest would probably be a 25-50 cent 8 pin microcontroller, every component/function you mention could be done with e.g. an 8 pin AVR 8 bit uP with almost no external components. a couple capacitors and diode for a charge pump and an LED, maybe, and the button.

Reply to
bitrex

Don't forget design time as a cost factor. With the uP solution I could have a working prototype of the design coded, uploaded, and up and running on a breadboard in about 20 minutes

Reply to
bitrex

How many? Ten or ten million units per year? If on the ten side, a PIC. If on the ten million side, maybe an ASIC but how sure are you of your market?

Reply to
krw

What you probably have is a 1 watt LED "flashlight" with an AMC7135 linear current source and a PIC controller to provide PWM (pulse width modulation) for brightness and flashing control. The minimum for a light is one AMC7135 per LED, and a simple on/off switch in series with the batteries. A little better is one AMC7135 per LED, and some kind of PIC or Arduino controller operated by a push button. Since the PIC or Arduino is programmable, you can make the flashlight do weird things: (Note: Hexbright is closed but you can roll your own).

This board controls 4 LED's.

More on the AMC7135:

More info under Candle Power Forums: and Budget Light Forums:

When you are able to deliver a clear description of what you are planning to design, perhaps I can offer some better suggestions.

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

Use an 8 pin AVR 8 bit with a multichannel differential ADC along with a low input voltage boost converter with a shutdown pin like the TPS6120. The AVR can high-side current sense its own input supply current with just a sense resistor in the supply bus cuz the ADC input channels can operate up to 0.6 volts over the supply voltage. It can also measure its own supply voltage.

With that info you can just hang LEDs off the PWM output pins and drive them "constant voltage" (with high frequency PWM) using one free PWM channel to modulate the shutdown pin to regulate power into the IC. The TPS6120 will operate down to 0.5 volts on its supply input; drain those AAs for everything they have.

You could implement some algorithm to match the circuit impedance to the battery impedance to reduce output power gracefully as the batteries are depleted.

Reply to
bitrex

Even the boost converter might be redundant, might be able to get away with just an inductor, didoe, FET, and another pin. Nowadays 50 cent uPs often have so much onboard hardware, ADCs, band gaps, dead-time generators, temperature sensors, PWM channels, etc. that in non-critical applications using any other ICs at all should be given the Muntz side-eye.

Reply to
bitrex

Some people like to make life difficult. All those functions need are an oscillator with it's output current limited. high: osc stuck on medium: hf oscillation blink: lf oscillation

NT

Reply to
tabbypurr

It sounds simple because you haven't answered any of the more difficult questions about that proposed topology i.e. what kind of oscillator do you use, how do you power it, how do you current limit it, how do you adjust its frequency in a cyclical way in response to a sequence of button presses vis a vis the spec. Like, the devil is in the details, man.

I guess we're assuming he wants to use a white LED as the "lamp" the OP doesn't specify. But you can't run a white LED at any significant power directly off 2 AA batteries in series.

Reply to
bitrex

I have three of these, all bought at different times, though they don't have a flashing mode, just full and half beam. (They're German and I believe flashing is deprecated there.) They also have a low battery warning LED.

They use 4 AA NiMH cells and all have a single 8 pin SOP with a few passives. The three SOPs have different markings, none of which Google.

I would guess that the switch doesn't control the power, just changes state - one of which is sleep mode - so the memory is volatile, possibly RAM or just a register or just a couple of bits.

Cheers

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Clive
Reply to
Clive Arthur

It's actually the norm at this time of year. The Germans have never been shy about getting their kit off and letting it all hang out. AIUI, it's not an arrestable offence in Germany to get your tackle out in public like it is in the UK.

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Cursitor Doom

Americans on average are unhealthily prude-ish but the Germans and Japanese it's just like wtf is wrong with them, government-sanctioned swingers clubs and selling little girl's panties in vending machines and shit, damn.

And no, they was like that before the modern Left showed up, sorry.

Reply to
bitrex

If anyone can translate the above for me, I'd be very grateful; thanks.

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Cursitor Doom

I met a gentleman from Glasgow once, he'd had a couple beers. Seemed like a very nice fellow. Couldn't understand a word he said.

Reply to
bitrex

Atmel's ATSAMD21 32-bit ARM M0 controllers are 40 cents, qty 100. Other less-powerful controllers are cheaper.

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Reply to
Winfield Hill

It's a really strong regional accent they have there. I can't understand them either. Likewise people from Newcastle-on-Tyne and Belfast.

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Cursitor Doom

You're right about the flashing mode in Germany. StVZO regulations forbids flashing lights: StVZO defines the MINIMUM requirements for bicycle lighting. That usually means an StVZO compliant light is a fairly decent flashlight but with plenty of room for improvements. I have a cheap StVZO light. Like all such rules, StVZO is controversial, especially concerning the required beam pattern.

I run mine also on 4AA NiMH cells in series. I could easily convert it to run on 14500 (AA size) LiIon cells, but don't want to risk destroying the light.

The PCB is much like your describe: U3 is the common 7135 analog current regulator. No visible markings on U1 and U2. My guess(tm) is U1 is either a PIC or an Arduino controller, while U2 is a BJT or FET for driving the low battery LED.

Nope. The switch interrupts the power. C1 keeps the controller chip power on long enough for the controller to recognize that there's been a momentary power failure. It then uses the chips brown-out or power failure alarm to switch flashing modes: "HOWTO: Making your own digital driver"

Drivel 1: If you're designing your own flashlight (not bicycle light), see the ANSI/NEMA FL1 standard:

Drivel 2: If you are interested in measuring the total light output (lumens) of a common flashlight, I contrived a very simple method that does NOT require an integrating sphere, but does have some major limitations in the area of beam pattern, non-circular spots, and accuracy:

Drivel 3: Most of the battery capacity (ma-hrs) and lumens output specs for various batteries and lights sold on the internet are highly eggagerated. Caveat emptor.

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

The UK accents I can probably identify immediately are RP, Cockney (not hard), Cornwall, Bristol (all the "country bumpkin" characters in TV and film seem to have that one), Sheffield/northerner, Scouse, various kinds of unintelligible Scottish like that guy.

Reply to
bitrex

I'm not familiar with such devices and can't comment on whether your design scheme will work. However, I did notice a few things that might cause problems.

Reducing the output power gracefully by matching impedances isn't efficient and sounds like an analog scheme. Flashlights use PWM (pulse width modulation) to adjust the brightness. Because the pass device is either on or off, but never in between, power dissipation is reduced and battery life is improved. Incidentally, battery life and SoC (state of charge) are important considerations as it would not do to have the battery die in the middle of a nightime bicycle ride.

With todays high power LED's, it is possible to design a headlight that is too bright. Besides blinding oncoming traffic, such a light also has a rather short battery life. However, that's todays fashion (driven by the equation more lumens = more sales), and is unlikely to disappear. Higher power LED's implies higher currents and more heat. Keeping the LED's from overheating is a major problem.

Your suggest of combining as many functions in the controller is a good one, but is limited by the power dissipation of the controller chip. A low end 1 watt headlight would draw about 270ma from a LiIon cell, which I suspect is more than a controller chip can handle. A series pass FET would probably be required.

Higher power lights, that use more than one LED, are often series connected to minimize connector and device current handling requirements. A boost converter would be necessary to run these, but it's cheaper to just add an extra LiIon cell for 2 series LED's.

Design of the optics is far more important (and more difficult) than the design of the electronics. The last thing you want is a small bright hot spot directly in front and nothing to the sides or in the distance. I've done some tinkering using ImageJ2 software for displaying how uniform the beam footprint appears on the ground. If you look at the original B&W photos, the beam pattern looks fairly even. However, add some pseudo color and the variations are much more obvious.

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

Google Assistant to the rescue. Now, you can have it talk (and listen) in various accents that are vaguely based on English: At this time, it has English (US, Canada, UK, AU, India, American Samoa, Austria, Botswana, British Indian ocean territory, Denmark, Fiji, Germany, U.S. Outlying Island, etc. There should be a list somewhere, but I couldn't find it. I don't think Cockney and other UK regional dielects are currently available, but if you provide Google with a feature request, your wish might come true.

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

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