alexvh's firmware. Update: Hidden strobe, Ramping and optional mode memory added.

I used 10 bytes and counted the number of bits that changes after a power cycle. I found that the percentage of bits that change value converges to 50% pretty quickly and consistently.

My conclusion is that the time constant for data retention in SRAM is too low for our use.

OTOH, the off-time cap on one of my drivers still gives me a nonzero value after being powered off for like an hour.

I could totally put in an easter egg where if you leave the thing off between 20 and 21 minutes, it’ll blink out the morse code for “pants are optional”.

Looking at Figure 7 in the paper, the transition region labeled Stage 2 is too narrow to reliably detect between long and short off time. Furthermore, the duration of each stage is dependent upon the capacitance of the power supply smoothing capacitor, as shown in Table 5.

In Section 8 on page 13, the OTC method is described as an alternative.

Yes, exactly. I meant that we currently check a byte to determine a short press. Right now in my firmware I just check if the entire byte is still 0, if it is, that means that no bits have decayed to 1.

Also from the paper:

After some experimentation it seems about 74% of bits in SRAM favour a state of 1. Even after really long off time 74% of bits decay to 1 and the remaining % don’t seem to decay. So it is better to set all bits to 0 and measure how many have decayed to 1.

I’m still experimenting, but this method looks promising. I don’t have a way to shut off the attiny for a measured amount of time, but just doing it by hand I’m able to see that longer presses result in more decay. Short presses of less than 500 ms result in no decay, which we already knew.

Here’s some quick measurements:
off time | % of memory decayed
615ms 8%
780ms 33%
825ms 40%
925ms 56%
1250ms 67%
1600ms 69%

I think this method could probably work.

I used 32 bytes of SRAM in my test. I counted the number of bits that are equal to 1 and output it as pwm so I could read it as a percent with a multimeter or oscilloscope by measuring duty cycle. Here’s my code if anyone wants to play with it:

Cool, so maybe we can get 3 levels after all. :slight_smile:

I didn’t expect it to have a long enough decay window to be useful.

Alex, those are good findings. I performed my test on a breadboard and so there are differences such as capacitor values and lack of voltage divider for LVD. Both of these will affect the decay time due to dropping Vcc. So your results with actual driver trumps mine with breadboard.

Originally I had initialized SRAM to patterns with equal 1s and 0s. I then tested all 1s and all 0s and found that all 0s work best. This agrees with your results.

I think the stack is implemented using SRAM, so that may explain why you are getting 74% max decay rate. Can you try inlining the hamming_weight function?

I’m only checking 32 bytes, half of the total SRAM, and I declared it in my code. So I’m not checking any of the SRAM that would be used by the stack. I believe only 74% decays because the remaining SRAM just prefers to stay at 0. 74% of the bits seem to end up 1 whether I initialize to 1 or 0 so I think it’s just the hardware. I’d like to see some other people test this so that we can see what the decay rate for other attiny13’s is and how much it varies. If this is something that varies a lot and requires calibration there is probably no point to doing it this way, and the capacitor mod would be the better solution.

Also, does anybody know what off times correspond to short press and long press for firmwares that use the capacitor mod?

I’ve been using:

  • Short: < 0.5s
  • Medium: 0.5s to 1.5s
  • Long: > 1.5s

So, the measurements shared a few posts ago look very promising.

If this method works, and if it can work with a smaller array, I’ll probably add it to my no-OTC firmware. I never did fill those 262 bytes I freed up by switching from on-time to mem-decay… :slight_smile:

Good stuff! I’ll be testing this out on my ATtiny85 firmware tonight. Being able to do this will save me from using the reset pin as an IO, and that’ll be a major headache saver.

I did try something like this as soon as I had tested the simple 0 method, but I only tested with a single byte and only checked if the value was 0, 255, or anywhere between. I got some results but they where not reliable and put on hold. Counting individual bits in an array of bytes will give much more reliable results for sure. The ATtiny85 has 512 bytes of RAM so I can use more bytes for better resolution.

With the ATtiny13A one should pay a lot more attention to RAM usage when using this method as it only has 64 bytes of RAM. Adding a 32 byte array to an existing firmware with many features could exceed the 64 byte RAM capacity, resulting in unpredictable behavior.

I tried it with the attiny13 in my edc flashlight as well and it seems to decay to 70% 1’s. So maybe attiny13 SRAM tends to favour 1 in general.

It should be possible to use less bits for this. I just wanted to get a large sample size so I used 256 in the test.

I’m going to try to put this into a firmware soon and see if I can get it working reliably.

Getting 70% on the ATtiny85 too.

Been testing and it is working with three levels, but the testing made me realized that for me personally the decaying starts too late to use it for detecting three defined off time intervals. I’m used to my off time firmware where a medium press is well under half a second. For me it’s just easier to use double and triple clicks rather than holding the button for as long as it takes to get a reliable difference between off times.

Do you share your code anywhere? It sounds like you’ve got a lot of interesting projects which others might want to see, and I’d be happy to include those in the shared repository.

I have a firmware with a medium press. It’s a little hard to actually get a medium press though. It might be possible to get it working nicely by using more bits and trying different thresholds for the medium press. Right now it uses 32 bits and a medium press is less than 20 bits of decay. Anything less than about 800ms seems to be a medium press.

I created a branch on github if anyone wants to try it out and experiment with different values:

Maybe it’s just the times for each type of press, but I think I agree with Mike C. I’m not sure if I like a UI with a medium press.

Never! The ramping mode doesn’t use the eeprom. I store the value in SRAM, and it stays there until the next power on as long as it’s off for less than about 500ms. The firmware doesn’t actually touch the eeprom unless you enable mode memory.

Once I’m done with my 85 firmware I can share it if there is interest, but it’s not going to be ready for a while. It’s pretty well organized and commented so it could be useful for others wanting to get into 85 programming, or AVR programming in general. However, it uses the I/Os differently than the standard Nanjg driver, but is easy to understand and change pins as needed.

That’s what I really like about this. I might not be a fan of the different lengths of off times, but I’m all over the method of using the no init area. I’m stashing all kinds of stuff in there. My 85 firmware I am writing has a user reprogram mode where amount of modes and level of each mode can be set, and I’m using the normal short “brownout” press to do all the programming, only writing to the EEPROM when everything has been configured.

I also have the integer for the voltage readout in there so it’s always updated when the light is on and under load. When I do my voltage readout routine (three short presses) I blink the level that was stored there. Then I get the current level (not under load) and blink it out if it differs from the “under load” value.

I’ve got so much space in the 85, plenty of ideas and don’t have to worry about limiting myself… yet… Like a user enabled lock out code or similar. Who wants their children to be able to flash 10000 lumens in their face if they find the light lying around on your desk, or set fire to your backpack because the switch was bumped while hiking. These days lights are getting dangerous…

Stashing arrays, bytes and flags into the no init area without having to read and write between each press has made this all sooo much easier… So yeah, thanks again :beer:

I have 5 pieces of Attiny85V ready for your new firmware. Thanks for your guys’ effort for us to have a perfect flash light what we want.

I should perhaps mention that the 85 firmware I’m coding is written with standard clicky button only in mind. I do have a few projects with both clicky and E-switches that I’ve yet to start coding (have all the hardware), but they all use the ATtiny24 or 84 which is a 14 pin chip.

14 pin chip is perfect for bigger light such as lantern and has more I/O pins to play with.

I’ll be posting threads about the lights when I get around to them… Ahh, so many projects, so little time… And heading for a PC free vacation week on Sunday.

Anyhow, don’t won’t to hijack this thread any more with my off topic clutter. I’ll make new threads when I have something to show.