Sounds great. I sent you a PM, might be interesting.. keep us updated. :)
O.K. then,……. I will be putting aside my PIC bias in favor of the AVR for the collective good? :).
It looks like the SOIC8 chip footprint is going to fit, with some re-juggling of the passives.
@NightCrawl - back at you. If you want to further discuss a higher amp version you can continue it in your 1 cell buck bosst thread (I,m subscribed).
Could 3 of those buck/boost chips be used to get up to 3 amps? If so, would they fit if the board was double sided (components on both sides)?
I don’t think so, as how would you synchronize the outputs? If you diode OR’d them together then there would be the reduced efficiency/output? I think you would go to a different single chip solution for the sake of board space (at least for the 17mm form factor).
A 3A solution should be a separate thread, and like I have said, I’m not going to put much of my own time until the 1A is sorted.
Questions for AVR junkies: Any reason why the ADC1 pin couldn’t read the VCC pin directly? You don’t have to have an inductor/cap combo for reliable ADC readings do you?
Dont worry, we wont derail this thread. :)
But a quick look at the linear.com page shows several boost-buck chips, some handle more than 1A. But sadly I dont understand quite enough of that stuff.
PIC? Tab closed, why would you use PIC over Atmel? Not to start a flame, just want to see what made you pick PIC over Atmel. Size, price, features, speed, memory, consumption, programmability, …
I can’t say I have a need for a 1A buck-boost, 7135s do the buck well. I would be great thought to have a driver that can supply constant power to the LED by drawing more amps out of the battery when it has lower voltage to supply.
I guess it’s still useful for people with NiMhs to have buck-boost 1A. At this power I think I’ve seen some though.
Hah, hah, I’ve heard countless discussions about the PIC vs. AVR. Sometimes it just boils down to what you started with (PIC for me), the time invested, and familiarity. I have nothing against AVR, just not as familiar with them.
To read the battery voltage you will need to configure the chip to use the internal 1.1-1.2V bandgap reference. Usually the ADC can only measure voltages up to the reference voltage so you would need a voltage divider on the battery. Note that high impedance voltage dividers can affect the reading due to the time it takes to charge the sample and hold cap. You may need to adjust for the reading that you get.
Close tab…minus 1 for AVR. The PIC also has a 1.024V internal reference, but with the advantage of a 2x and 4x multiplier, no voltage divider needed. Boo Hoo.
I may go back to the SOT23-6 with the programming pads broke out for the PIC or AVR?
Even with a 4X multiplier you can’t measure a fully charged lithium cell… but may not matter if all you are doing is low voltage cutoff.
Also, forgot to mention that the TINY85 has an on-chip temperature sensor. Not very accurate unless you apply a calibration factor.
Yea, not interested in voltages over 4V, lets hope the charger is doing its job. I’ve tried a newer PIC with the internal temp sensor, and danged if I could get any sensible numbers.
This is madness!!! I gave in, 3 passives on the bottom copper. Plus a good looking rats nest for hooking up the programming pads . If this board works out, it will be a miracle :).
It’s is impossible to run a good rule check, because DesignSpark gets real funky with all the components loaded up inside a smt annular ring (i.e. the outside copper strip around the diameter on top/bot). May have to devise a work around.
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Edit: Oops, I see I left the PWM track off. Fixed it
I see, AVR, ARM, seems easier to get into from my limited experience. PICs are used a lot yes, but never much for hobby projects? At least I did not notice.
I would go based on hardware advantages/disadvantages for a particular application irregardless of what I already am familiar with more.
Otherwise I like the LTC3454 specs 
There are many dedicated PIC hobbyists, but could be a regional/geographic related thing? The forum at (See electro-tech-online.com) is big on PICS. The other thing could be the time frame when entering the microcontroller field. When I entered 6 or 7 years ago, the AVR was in my view a niche market for the hobbyist, Arduino was just coming out, and their code library’s were barely getting started. Now all the hobby focus seems to be on the Arduino (AVR).
I love the fact that all the the new ARM development boards are super cheap. Just haven’t found a project that needs that kind of power.
A couple of questions:
1) Is there a source for battery springs like on the Nanjg 105C? My battery pad is down to 5.8mm, so will need a 5mm spring like the Nanjg.
2) Some of my components are riding pretty close or onto the GND ring. So is there a typical width of support in the battery tube these drivers fit on? Like say .020”-.030”, or more?
I have the TI Stellaris, got it presale for $5? Shipped. Now it’s $12-15? + shipping. USB powered, works off a ML-102 with 18650 0:)
Yes Arduino made a big boom with all the easy extensions and code for it I suppose.
But it seems expensive to me and overhyped. Unfortunately it does have a lot of boards and extensions that other platforms probably do not or at even higher price.
For simple things Arduino seems like a price overkill and it can be done with other boards that are cheaper.
There is PICs for sure, more in the professional applications, –10years. Dunno what is used nowadays. As I see it what you had to build that time before now you just buy a chip that already does the whole thing :bigsmile:
That is a really cool idea on the ML-102, Thanks for sharing!
I don’t want to rain on the parade here, I’m just thinking while typing I guess. Based on the typical Li-Ion cell discharge curve, I do not see the necessity for a buck/boost with one cell, one LED. I could be missing something so please correct me in if this doesn’t make sense.
- Typical Cree LED (XM-L XP-G, etc.) have a Vf of around 3.0V at 1A.
- AMC7135 has 100mV dropout.
- Assume 150mV loss in tailcap, contact points, and wiring (For me I always copper braid my springs).
OK, so from 4.2V down to 3.25V (3.0 + 0.1 + 0.15), the 7135 can drive a full 1A to the LED.
Below 3.25V the output will start to drop off.
Efficiency while the 7135s are in regulation is between 71(4.2V) and 92(3.25V).
Most buck regulators are 80-90% efficient, with boost in the same ballpark. For this buck/boost driver, (ideally) it will do a power conversion down to ~3.0V when VBatt is above 3.15V, and up to ~3.0V when Vbatt is below 3.15V . I say this is ideal because I did not factor in any dropout for this regulator. I assume there is some, but I only used the tailcap losses here, giving this regulator a slight advantage in the comparison.
That last part is where i see the critical weakness; Li-Ions have virtually no energy left below 3.15V. Furthermore, you will need to cutoff around 2.75V (no lower than 2.4V) to preserve the longevity of the cell.
As I said earlier, I may be missing something so please correct me. However, the majority of applications (i.e. Cree LED based flashlights) this will not gain much at all.
Moving up to 3.0A and putting Vf at 3.3V there is a little more of a requirement for buck/boost, but the cell energy is still mostly gone. I suspect this would give a few extra minutes of full output, tops. I personally prefer the ramp down in output as the cell depletes; it extends run-time when I may need it most.
relic, you have to consider 4.35V cells and the NCR line of Panasonic. I think a well regulated driver could increase the runtime by about 25%. Also if you use a Nichia 219, this will come in handy because it has a vF of ~3.5V @ 1A and 3.7V @ 1.5A.
nickelflipper: About springs, there are for example these:
http://www.intl-outdoor.com/goldsilver-plated-springs-for-drivers-and-switches-5-pcs-p-325.html
About the place in a dropin.. I could measure tomorrow. You dont happen to have a dropin lying around? But I would say that the driver diameter is 17mm while there is rougly 0.2mm on each side for the driver to sit on. If you need it exactly, I can go measure tomorrow.
@relic38
Rain? What Rain?
I would have thought the AMC7135 would have been a little worse for the wear at the higher battery volts, but that was strictly a gut feeling. Is there a link to pass along on AMC7135 efficiency tests or charts?
A solution looking for problem perhaps. I will continue to follow thru for the sake of science and experience. The buck boost driver isn’t going to be cheap, the LTC3454 is $3.92 in single quantities from Digikey. The AMC’s are hands down best bang for the buck.