Iāll have to take your word for it. My worry was that youāll take the power being dissipated by eight 7135 and now have it all in a single FET. It seems like a lot to me but Iāll admit itās just a very rough guess, I havenāt looked up any specs. I might try it and come back with pictures if I burn something
Granted, but itās convenient because you already have a heat sink for the LED anyway. Also, itās not obvious to me that running the LED at very high current is much worse for efficiency than wasting power in the FET or 7135s. This probably depends a lot on the LED involved.
Anyway, how would you go about it? All I can think of for good control over the whole range is to build a crude 1bit DAC for the FET gate. I think it could be really poor if feedback from one of the ADCs is used to hold the output steady instead of having to rely on precalibration.
Hardlyā¦ the FETs designed 25+ years ago tend to be quite different from more modern FETs (e.g. smaller process geometry, cell sizes) You have to look closely at the spec sheets to see how they will work in DC/linear operation. Assuming your shiny new FET will work the same as your 25 year old beastie is not a good idea. Now a flashlight running at 5 amps may not be an issue, but if you are using a tiny SOT23 fet, it may be. The only way to be sure is to check the datasheetsā¦ and often the relevant info can is very well hidden / non-obvious.
I have designed power controllers for up to 7.5 megawatts. My CD spot welder does 500+ kW pulses. At those power levels the devil is in the details. Magic smoke / silicon plasma wants nothing more than to be free.
Led4power made some drivers which work this way. He has a whole family of drivers available for purchase.
Efficiency was better and there was no pulsing in the output, but the driver itself has overheating issues in the medium-to-high modes. Itās fine on low and on maximum output, but in-between it tends to cook itself. Moon (~4 lumens, not 0.2) operates separately due to problems doing moon from the FET. I recall some issues with ālowā mode too, like it was a little unstable and itās ~60 lumens instead of a single digit and it canāt really go any lower (probably for the same reason the moon mode operates separately).
Unfortunately, led4power hasnāt released any designs or code and the MCU isnāt a type which can be reflashed on-board. Itās a nice product, unsurpassed in several ways, but it hasnāt been very widely used.
Based on led4powerās drivers and the test results for it, I think a linear FET would be a nice way to increase efficiency on modes between ~80 lumens and maximum output, if the driver has good heat sinking. A separate power channel would still probably be required for modes between 0.1 lm and 80 lm though.
Some common code has already been exported into shared headers to avoid duplication. Other parts tend to be different per project, and very different for different types of switches. There is still more de-duplication to be done, but this is very limited due to the ātinyā nature of the attiny.
Nothing available yet. I know a lot of people advocate releasing often but I have had enough talks with people that prefer to wait for a version that is tried, tested and approved. I have a whole pile of old obsolete versions of driver boards that are of no use to anyone. I would hate to have had people waste time and money on those versions, only to hear me say that I donāt support them anymore because I have a new design. Also, I have the FET on the dreaded reset pin (all other pins occupied). It took me a lot of swearing and hair pulling before I managed to build a device for high voltage fuse resetting and get it working. Updating the firmware is by no means an easy task if you do not have a working HVSP fuse resetter, because then you have to make/get one and figure all that crap out.
There are two major differences. First, I have E-switch, voltage monitoring and off time cap all on the same pin. This requires a whole different approach to the firmware. For example I have to have delays on the voltage monitoring because of the off time cap charging and E-switch presses. I have to run the watchdog interrupt at full speed in order to detect E-switch presses instantly, and disable all voltage monitoring until a moment after releasing it. The voltage divider resistors are much higher than āregularā ones as R2 on the divider becomes a bleed/pull-down resistor for the off time cap.
The second difference is that I run any number between one and eight AMC7135s fully on (constant current) and use a single PWM dedicated AMC7135 for all brightness levels between. So all of my mode values consist of two bytes, a PWM value for the PWM decicated AMC7135, and then the amount of AMC7135s I want fully on. Itās a constant current/PWM hybrid.
I have had no such issues. I donāt have any gate resistors or capacitors on the FET, and can happily switch between moonlight low PWM values on the PWM AMC7135 and full blast on the FET without hickups, using both off time mode switching and E-switch mode switching. Iāve been following these discussions with interest (where to put the input cap and so on) but as I have not had any of these issues myself I have nothing to contribute towards solving them. The FET I use is the NXP PSMN3R0-30YLD if that matters.
Except awesomeness, and possibly some of the answers.
Seeing the differences in board design might make it clear why one design has issues while another does not.
Plus, the things you built by yourself are some of the most fascinating and exciting projects on BLF. You may think of your old boards as obsolete junk, but the ideas within, and the details, could potentially be the basis or inspiration for all sorts of other projects. Itās not just the final revision which matters; the things you learned during development would also be beneficial for other people to know. And youāve downplayed the value of your code by saying it requires different hardware and different approaches, but variety is exactly what BLF needs to grow and move forward.
Itās a good idea. However the FETs donāt perform well at moon to low levels in either PWM or linear modes, so a separate power channel is still likely required to get those levels to run well.
Iād have to check again, but I think led4powerās drivers use a separate thermal sensor to regulate themselves since heat is so much more important on a linear FET design. As for learning algorithms or PID, I looked into PID while doing the bistro thermal code. A fairly simple PID algorithm doesnāt fit onto the MCU, much less a nice-quality PID algorithm. DrJones recently tried to do it too, reduced the size until it would fit, and found that it behaved very badly. He ended up taking the same approach I used, which is basically just an incremental correction factor with a really strong lowpass filter to avoid bouncing.
So, it can work, and it improves efficiency quite a bit on medium modes. However, it also adds some significant complications. Eventually someone will probably decide the complexity is worth it though, and dive in. We already know it works; it just needs someone to do it.
There are other interesting ideas to explore too, like boost and/or buck drivers. Itās possible those might be developed first, since at least one is already in progress. Thereās also the many-7135s approach already in use, which provides some of the linear FETās benefits but without the heat issues. All sorts of interesting stuff happening lately.
Check out Dale Wheatās LED dimmer code. He uses a PID (actually a PD) for doing smooth fades in his LED dimmer. Link to the source code is in the description. Iāve used his dimmer for lots of stuff. Modified the code and for a TINY85 to control a 5000 watt composite curing oven using a PID. I modified his circuit board with a better FET/heat sink/regulator. Also modified one to do PID based control of a fan prevision temperature control of ovenized crystal oscillators. By changing the regulator to an LM2936 and a couple of tweaks to the firmware the off-state current draw is under 10 microamps.
Cool. Iāll have to look at that in detail next time Iām working on the code.
I didnāt go into much depth when I checked out PIDā¦ just deep enough to see that the reference code was orders of magnitude bigger than I had room for, so I went with an extremely simple approach instead.
ā¦
Edit: I was too curious, so I looked at the code. Heās doing pretty much the same algorithm I did for the āsoft startā thing in bistro, which makes smooth transitions between different output levels. Thatās not really sufficient to make thermal regulation behave, but it works well for traversing arbitrary adjustment distances in constant time with a smooth-looking ramp.
Edit 2: The āsoft startā and dimmer adjustment algorithm is:
Are we there yet? If so, stop. Otherwiseā¦
Go about a quarter(ish) of the remaining distance, minimum 1 unit.
Looking around a little more, I think I might have found a potentially-useful approach. Thermal regulation is rather unpleasantly like trying to steer a really heavy ship. The high degree of inertia makes it hard not to over-steer. Bistroās solution is to steer very very slowly.
Hopefully I wonāt put my foot in my mouth, but it seems to me that PID shouldnāt require a lot of space. Here is an Atmel document on the subject (with code provided in a zip), as linked from the ATtiny85 docs page. Atmel claims that their PID function compiles to 534 bytes.
Well, I do have some true PID code for my reflow oven. It runs on a MEGA2561 and uses floating point code. It is pretty much the same PID/fan control code I used my GPSDO (GPS Disciplined Oscillator) temperature stabilizer. I have seen it control temperature with a 24 hour RMS error of 1 microdegree, with peak errors of less than 5 millidegreesā¦ Might be a bit much for a flashlight.
A simple temperature control PID is not much more complex than Daleās code. Implementing the I (intergral) term can be a bit trickyā¦ you have to handle āintegral windupā where the integral (long term compensation) value keeps accumulating in the same direction and āruns awayā
Tuning a PIDs control parameters is always a pain. Most simple method is to start with P/I/D values at 0. Increase the P value until the output starts oscillating and then increase the D value to stop the oscillation. Then adjust the I value to minimize long term drift. My oven / GPSDO code has some auto-tuning code to that does a lot of the work.
Hmm, 534 bytes. Not bad at all. Certainly better than the ~5k bytes one I looked at.
Iāve got a copy of the Indigo 5.2 firmware, but itās a little ā¦ opaque. Assembly code with sparse Russian comments. I think Atmelās version will be a more useful reference, and another Kalman link I found which deals specifically with compensating for situations where one or more values lag behind.
It wouldnāt be a big deal to devote an extra ~500 bytes to PID on a tiny45/85. I wonder how much the response curve can be improved with PID and/or Kalman instead of the āsteer really slowlyā approach, and if it can anticipate over-heating conditions and start to correct for it in advance. I also wonder if itāll need to use the full 10 bits of precision instead of 8, since temperature measurements are rather coarse so far.
Too many questions/unknowns. I need to just do it and find out. ā¦ ā¦ after I get more parts and some time.
Belive me, you donāt want to go down the Kalman rabbit hole. Insanity awaits those foolish enough to enter that dark realm. Iāve been there and barely escaped with my life. Bits of brain still ooze out of my nose whenever I think about it.
Been away climbing for a while, sorry for late replies.
It works very well, Iāve been using it in several lights. Itās all just voltage measuring, and deciding what to do with the measured values.
Individual pins with groups. AMC7135 groups are PWM, 1, 2 and 4. Another pin for the voltage input and the last pin Iāve put on either a FET or a larger group of AMC7135s. Iāve looked at using external components to avoid mucking around with the reset pin but on Iām all out of space for the solutions I could find. Iām not that knowledgeable with these things though, any good suggestions I could look at?
Thanks! In regards to board design I wouldnāt know why Iām not having the same issues. No funky stuff with the layout. And as far as I have been able to tell, these issues with the FET / moonlight you have been having have not been able to be resolved by firmware coding. What is the FET you are using? If it has the same footprint I could always build a test driver with one of them (if itās not the one I use).
Iāve been workān on a few older mods with the wight FET+1 driver v009 and a Attiny85 and noticed not all had issues. Couple didnāt need anything extra, while others needed the FET gate resistor and the 0.1 uF cap across the +/- input to the MCU. I use about always the SIR800DP FET, where itās been reported by others to be prone to the flash problem. Read somewhere that someone simply replaced it with a different P/N FET and the flash went away - donāt recall where or which FET it was though.
I tried pretty much everything in firmware to fix it, TK has also, and we couldnāt fix it.
I do have interest in temperature control. Currently I have temperature calibration and step down, and have a few first tests of temperature controlling. What advantages would a PID controller have? My testing consists of running a ālearningā routine where the light heats up, shuts off and does a few things, all timing how the heat behaves in response to turning off and so on, and then storing the values into the EEPROM. My main issue is that with some hosts the difference between doing this routine while holding the light as a lot different than doing it while it is laying on the table. Care to write a few lines on how a PID controller could be used to make all this a little easier?
Ahh, OK. That one was harder to get in Europe, I think thatās why I went with the NXP PSMN3R0-30YLD. Iāve not used another one. If I remember correctly the SIR800DP has a diffferent footprint so I wouldnāt be able to test without changing the board.
