*BLF LT1 Lantern Project) (updated Nov,17,2020)

Just to fully capture the differences between the two drivers pictured above (and we are only talking about these two for the moment).

FET driver provides PWM free light, at the expense of the button LED. This assumes no change from the ATTiny85 to a different part.
AMC driver uses PWM and is likely less efficient, but retains the button LED function.

Since Lexel added programming pads for the MCU, changing that to a more capable part than the ATTiny85 could be in play, Lexel suggested considering the ATTiny84 IIRC.

Not sure if there is a significant cost change with any of these options, I suspect it is <$5.

I realize this temporarily ignores the boost driver discussion, no offense intended.

Given the choice between the FET and AMC driver, I vote FET driver.

BTW Lexel, thanks again so much for taking over the driver responsibility, regardless of the choice BLF will end up with a much better product. Wish we had connected sooner. :beer:

I do like the idea of a button LED, and with the FET version we could go with a simple resistored low-power yellow or amber LED to keep the button glow night light as i did when i built the BLF Steam pipe light glow tube. (using a 12K to 15K 1/8w resistor and a low forward-voltage LED will glow for years on the four 18650s. (loosening the battery tube a 1/4 turn like the Q8 to lock it out would turn off the glow button LED when in storage for long periods of time.

I’m not keen on a boost driver design for reasons in this case as mentioned earlier, and would just add more time to start over from cratch again. Lexel’s designs above gets my vote & approval for the lantern project.

Please sign me up for 3. Looking forward to it all coming together into final form!

Sign me up.

quijibo gets interest list numbers 965, 966, and 967.

wigglybroom gets interest list number 968, and a hearty welcome to BLF :beer:

This may be my last post regarding additions to the interest list, as huey18 is writing some code to automate this, so I may be totally out of a job on this project. :cry: :stuck_out_tongue:

I vote for fet. Boost or buck would be more efficient, but costlier. And with 4 cells it will run forever for all my purposes.

As we only have this options I also vote for the FET driver, but I would go with a more efficient (boost) driver all day even if it would cost a little more. Maybe Lexel could design one and sell it separately to modders.

I already have most of the code written. I just haven’t been able to actually try it since the hardware doesn’t exist yet.

The light operates the same as any other Anduril light, but with one key difference: While the light is on, in almost any mode, the user can “click, click, hold” to make it change tint. This happens smoothly without significantly affecting total lumen output. If the color changes in the wrong direction, let go of the button and do it again.

+1

I’ve been testing some LH351D emitters and I ended up with green ones. For the lantern, it’d be good to make sure we get something at or below the blackbody line if possible.

I linked the tint and UI to this discussion just to give perspective how unimportant I think it is which actual driver is inside if in reality you do not notice it anyway, unlike tint or UI which are obvious in practice. You will not easily notice a 10% longer runtime.

But a 30% efficiency gain is something that I agree is worth trying to get, that is something that you do notice on the outside.

Some thoughts on this…

Advantages to PWM / AMC7135 chips:

  • Better tint. LEDs get less white at low power, and these are expected to run at fairly low current. PWM runs at a consistent power level and produces a consistent tint regardless of how many lumens are coming out, but a constant current driver has more visible tint shift when not running at full power.
  • Can keep the button LED. PWM doesn’t require as many MCU pins, so we could still have a lighted button with multiple modes. The linear FET option may also have higher parasitic drain in standby mode, due to needing a voltage divider to measure battery status. This effect could be very small though, if done right.
  • Manages heat better. The 7135 chips spread heat across a wider area and have thermal regulation built in, so they don’t overheat. However, a linear FET concentrates heat into a smaller space on the driver, which means the driver itself may need heat sinking.
  • Better low modes, usually. The “raptor claw” 7135 chips have good performance in low modes, so the bottom of the ramp should be pretty low and pretty stable. However, a linear FET tends to have difficulty in really low modes, so the bottom of the ramp might not be very low or very stable.
  • Simpler driver design, easy and pretty much risk-free.

Advantages of a linear FET:

  • Higher efficiency in most modes. More lumens or more runtime. At the lantern’s power level though, this effect may be small, like only a 5% or 10% difference.
  • The parts might cost less.
  • Can potentially be modded for higher current by changing a sense resistor, but this also increases the risk of driver damage due to heat.

I’ll get things working on whichever one is used, but personally I lean a bit toward the simpler option even if it’s a bit less efficient.

Thanks for your thoughts TK, and what if a boost driver would be developed, can that still have all the features of a 7135 driver?

lets go with the FET, most people dont care about 10% average efficiency gain for a more compley and costly boost driver

pinout
PB0 enable of Boost USB and the opamps
PB1 3000k
PB2 voltage divider 220/47k for LVP
PB3 switch over 1k
PB4 5000K

If we need the 7135 chips for the button LED and the FET struggles with low currents why don’t we just use a combined FET+1 design?

Well actually… :stuck_out_tongue:

* GD&R *

Tint changes with current, and is usually best (whitest) when the current is in the medium-high range of an emitter’s power capacity. Tint is generally worst at very low power levels, or when the emitter is heavily overdriven, but fine anywhere in-between.

Here’s a video of a single emitter changing color due to different power levels being used. The light on the right is alternating between 350mA constant current and 350mA via a pulsed FET. The light on the left is only there for reference. http://toykeeper.net/torches/blf-a6/tintshift.avi (sorry for the bad video, I should re-do this demo sometime)

For the lantern, the risk is using too little power, causing unnecessary tint shift because the emitters aren’t running hot enough to get to their ideal range. If it’s only 1.4A total, split across 4 to 8 emitters, that’s 175 to 350 mA per emitter at the highest brightness. This is low enough to get some tint shift, but not a lot. However, a constant current driver will get worse tint shift as the total power goes down, while a PWM driver keeps a constant tint.

But between a linear FET or a buck/boost driver, tint shouldn’t be any different. They both shift the same way at low levels. The only style which doesn’t is PWM.

At least the effect doesn’t seem particularly bad on the LH351D. I notice it a lot more with XP-G2.

It doesn’t work that way. It wouldn’t really help anything.

The linear FET’s extra pin is needed because of how that type of circuit works.

With a 7135 chip design, a pulsed (PWM) signal goes from the attiny chip to a set of 7135 chips, turning them on and off at about 16 kHz. This can be detected by measuring equipment but is invisible to the eye. It looks like a steady brightness level, and it mostly “just works” without issues. The 7135 chips don’t care about the pulse voltage, they only care about whether it’s on or off.

With a linear FET design, a PWM signal goes from the attiny to a circuit which averages it into a smooth analog voltage. At 4.2V and 50% PWM duty cycle, the output signal is a steady 2.1V. This tells the FET how much power to allow through. But the same 50% duty cycle on a low battery at 3.0V only averages out to 1.5V. So the brightness changes with voltage.

To avoid the problem of brightness changing with voltage, the attiny needs to receive a constant input voltage. Let’s say that’s always 5.0V exactly, using some magic on the VCC input pin. Then a 50% duty cycle always averages out to 2.5V, and the brightness stays the same regardless of whether the batteries are full or almost empty.

However, this means the attiny has no idea whether the battery is full or empty. So we have to add a second connection to the battery, to allow the attiny chip to measure battery status. This uses up an extra pin.


I see over 4V for about 600 mAh which is 18% of capacity, not 1/3.
Voltage decreases pretty much linearly to 90% capacity, from 4.15 to 3.4V. Then it falls off the cliff.
Over that 90% capacity, with Vf of 2.82 linear driver is about 75% efficient. Over the last 10% it’s about 91% efficient.
Overall efficiency is more like 78%.
A 95% efficient driver would increase runtime by about 22% in the lowest modes, less in the higher ones.

Is there any chance of using PB0 and PB1 for 3000K and 5000K, and PB4 for USB/opamps? The chip likes having the two PWM channels on PB0 and PB1. I’m hoping for something like this:

                 ----
         Reset -|1  8|- VCC
 (PB3) eswitch -|2  7|- voltage divider (PB2)
   (PB4) opamp -|3  6|- 5000K (PB1)
           GND -|4  5|- 3000K (PB0)
                 ----

Otherwise, the second PWM counter gets involved, and it runs at a different speed, and things get a little weird.

Also, how slow can the PWM signal can be without causing problems? I usually underclock the MCU at low levels to make the bottom of the ramp more efficient, but I’m not sure that’ll work with a linear FET.

If I understand correctly, the 7135 version might be something like this?

                 ----
         Reset -|1  8|- VCC
 (PB3) eswitch -|2  7|- USB enable (PB2)
 (PB4) aux LED -|3  6|- 5000K (PB1)
           GND -|4  5|- 3000K (PB0)
                 ----

I´m in for one!

Thanks for the clarification ToyKeeper :+1:
I actually thougt that we need one of the 7135s to drive the button led :person_facepalming: , I really shouldn’t read this while doing something else…

I didn’t say over. I said average. The midpoint of the voltage of the first ~1200mAh at a low discharge current (which it will be because there are 4 in parallel) is ~4.0V. My numbers were right for the scenario I outlined.