How do mode-remembering lights retain memory?

eg the Jetbeam LF2, Nitecore D10, et al.

I assume that they have to use some battery current to do so? Or are they stored in some sort of non-volatile memory? Seems like that would be pretty advanced for a flashlight.

Problem with volatile storage is that, in addition to losing the memorty when changing the battery, it would preclude long-term storage of the light with battery inside because the micro-amp discharge necessary for keeping the memory intact would drain the batt to zilch given enough time.

Discuss.

Okay.

Yes, many lights have what is called "quiescent current," where a very small, constant drain is present even when the light is "off." However, they often don't rely on it to retain a memory mode. Usually, it serves to keep the microcontroller minimally awake so that it can receive on/off signals.

As an example, the Nitecore PD series lights have a constant drain that would, for example, flatten a fresh NiMH in the D10 in about a year or so. However, they remember the last output setting through a battery change. The PD series are generally used as EDC lights, often meaning frequent use and frequent battery swaps or charges, minimizing the disadvantage of the quiescent current.

I guess it would vary from light to light.
I wonder how one would go about measuring it? Setting my multi meter to the 20A setting and testing my light without the tailcap just measures current draw as though it were switched on...?

kramer5150 said:

I guess it would vary from light to light.
I wonder how one would go about measuring it? Setting my multi meter to the 20A setting and testing my light without the tailcap just measures current draw as though it were switched on...?

Click to expand...

The 20A setting gives you WAY too low of resolution. We're talking microamps here.

Edit:
I measured my D20 at .018 mA. That's 18 microamps.

How do P60 modules retain memory? P60 hosts (at least Surefires) completely open the circuit when the tail-cap is unscrewed. Its not even possible to draw current, with the switched open circuit.

????

kramer5150 said:

I guess it would vary from light to light.
I wonder how one would go about measuring it? Setting my multi meter to the 20A setting and testing my light without the tailcap just measures current draw as though it were switched on...?

Click to expand...

If you have a light with a physical clicky switch, there is zero draw when the light is off.

Only lights that have a direct and uninterrupted connection to the battery like PD lights and (IIRC) TaskLED drivers will draw current when the light is off.

kramer5150 said:

How do P60 modules retain memory? P60 hosts (at least Surefires) completely open the circuit when the tail-cap is unscrewed. Its not even possible to draw current, with the switched open circuit.

????

Click to expand...

If it remembers permanently, it uses flash, possibly on the package with the uC. You have limited writes, but this can be handled in many ways, such as using flash that can be written to many hundreds of thousands of times, and/or waiting until power is off to write (I don't know how dangerous that would be, writing while caps power it to its shutdown). The interface for changing and setting modes, if any, can be used to encourage infrequent writes.

If it remembers only for some seconds, it is almost certainly using capacitors on the electronics to keep itself powered. Either it powering off, or a timer resetting, will get you back to the "off" mode. The uCs use so little current that even small non-electrolytic SMD caps can keep them powered for many seconds.

cerbie said:

If it remembers permanently, it uses flash, possibly on the package with the uC. You have limited writes, but this can be handled in many ways, such as using flash that can be written to many hundreds of thousands of times, and/or waiting until power is off to write (I don't know how dangerous that would be, writing while caps power it to its shutdown). The interface for changing and setting modes, if any, can be used to encourage infrequent writes.

If it remembers only for some seconds, it is almost certainly using capacitors on the electronics to keep itself powered. Either it powering off, or a timer resetting, will get you back to the "off" mode. The uCs use so little current that even small non-electrolytic SMD caps can keep them powered for many seconds.

Click to expand...

The Nitecore and the Arc 6 both use flash memory, integrated with the uC. The maximum number of writes is supposed to be around 100 000. But, if the integrated flash memory controller has wear levelling and the setting memory uses only 1 byte, this could be multiplicated by a nice number!

Bonky said:

....I assume that they have to use some battery current to do so? Or are they stored in some sort of non-volatile memory? .....

Click to expand...

The key is the type of "transistors" on the circuit chips. Some require power to maintain their state and some will hold their current state without power and only change state when triggered. In general, non-volatile is more expensive to produce, but with the limited use in a small flashlight circuit, the cost difference is probably miniscule.

If you are interested enough you're willing to study a bit, the Programmable Hotwire Driver project has a wealth of information:

https://www.candlepowerforums.com/threads/209098

Alan B, JimmyM, wquiles, and others have discussed tradeoffs and alternatives and left us a history of circuits, code, & experiments to study. The regulation part of the circuit differs from an LED circuit, (some, probably,) but the options and the control should be similar. The parts about retaining settings during off cycles relate to the NVRAM, the quiescent current in low-power modes, etc. (I honestly forget exactly what they decided. Any given light might decide differently, but I trust most of the options are at least mentioned by those guys.)

Oh, another option is mechanical switches. E.g. the L1D switches between Turbo & non-Turbo modes with a mechanical switch. I assume this is all the two-mode L1T uses, but I don't have one. Except for expense & reliability you could use a multi-step switch and select multiple levels, without any power drain or electronics.

Bonky said:

eg the Jetbeam LF2, Nitecore D10, et al.

I assume that they have to use some battery current to do so? Or are they stored in some sort of non-volatile memory? Seems like that would be pretty advanced for a flashlight.

Problem with volatile storage is that, in addition to losing the memorty when changing the battery, it would preclude long-term storage of the light with battery inside because the micro-amp discharge necessary for keeping the memory intact would drain the batt to zilch given enough time.

Click to expand...

Very few lights has quiescent current, and some (i.e. NiteCore) does only have it in some conditions.


But multi level lights are usual controlled by a small microprocessor and these processors very often come with some non-volatile memory, i.e. your just has to design the light with the right microprocessor and your have non-volatile memory for free.