D.I.Y. Illuminated Tailcap - gChart Editions

Flashlight Modding and DIY Parts
107

It seems to be working fine at the moment, but I’d be curious to hear your ideas! Here’s an overview of the code:

Main()

  • Initialize the clock and pins
  • Run the animation
  • Shut the LEDs off and pause for 20ms to allow things to settle down
  • Run Set_Battery_Status
  • Initialize the RTC to wake us up every 60 minutes
  • Go to sleep (standby)

The RTC interrupt just clears the overflow flag and then calls Set_Battery_Status

Set_Battery_Status()

  • Turn off all the LEDs
  • Wait 10ms for things to settle down
  • Run Get_Voltage
  • Use the returned voltage to turn on desired LEDs

Get_Voltage()

  • Set Vbandgap ref to internal 2.5V
  • Set ADC ref to VDD
  • Enable the ADC, set it to 10-bit resolution
  • Get 15 ADC readings and throw them away
  • Get 8 ADC readings and add them together
  • Get the average of the 8 readings (bitshift: sum >> 3)
  • Use a calibrated formula to get the voltage. Standard formula is (1023*2.5)/reading. My formula is (2643.3/reading)+0.0267.
  • Turn off the ADC
  • Return the reading

It’s probably a bit wasteful, but I have 4K of program space to work with and I’m just turning on and off a few indicator LEDs so I wasn’t very concerned about peak efficiency.

108

Good, I think I can contribute a bit there:
So you get 8 readings with your ADC, and then simply average them. I had these ADC reading problems with Arduinos and ATTinys as well, and I found an alternative to averaging to get better readings. I don't know if it requires less or more bytes though. Never tested it.

So the solution: get the median.
The median is the value that separates the higher half , from the lower half. To get that: Do your readings, and put them in an array. Then order them (ascending or descending, whatever you like), and take the value in the "middle" of the array. That way, a bad reading doesn't affect the value you get.
Small tip: use an array with an uneven length. If it would be an even number, you would have 2 middle values and need to take an average of those two.

I don't know how familiar you are with programming, so I'll just write it. Please let me know if you don't need code bits, it takes so long with the advanced post editor.

in C++:

//sorting array in ascending order

int i, j, temp, median;

int length = 9; //uneven is better

int array[length];

for(i=0, i<length, ++i){ //get value in array

for(j=i+1, j<length, ++j){ //get value next to it in array

if(array[j] < array[i]){ //if value next to it is higher, swap them

temp = array[i];

array[i] = array[j];

array[j] = temp;

}

}

}

median = array[(length-1)/2] //for an even length it would be (array[(length-1)/2]+array[(length)/2])/2

There's even a way without using a temporary int, here's just the principle:

int x = 5;

int y = 7;

x = x + y; //x now 12

y = x - y; //y now 5

x = x - y; //x now 7, swap done

109

Median - nice idea! I’m actually using that same methodology for my DIY lumen tube-logger. Its a Wemos D1 Mini running Arduino hooked up to a good light sensor via I2C. Anytime there is a change, the first reading is typically off. So anytime I do a reading, I actually grab three and return the median. That’s a pretty small sample size, but it works for what I’m using it for. But yeah, median can be helpful for dealing with outliers. I could probably get away with far fewer ADC readings by using it.

Ahh, good ol’ Bubble Sort! My undergrad degree was in Computer Science, and my go-to back then was C (I use mostly database and web languages now).

110

I assembled another smart tailcap and put it in a S41S (stainless, not colored).

New firmware this time: when starting up, it “dials up” the battery readout and displays it for 3 seconds. Then it goes into a slow rotate animation.

Hmm… I wonder how a pseudo-random “twinkling” animation would look?

111

I always thought it might look neat to do sort of a roulette wheel animation while waiting for voltage to settle, then take a reading and slow down the animation until it stops at a point representing the current charge. After that, I figured I would have it go into a low-power beacon mode which blinks the result periodically.

That was for a RGB tailcap though. I guess on a 8-of-the-same-color design it would display based on how many LEDs are illuminated.

112

As designed, I could use multiple colors of LEDs (perhaps 4 each of 2 different colors). I’m not sure how that would work for a roulette animation, but it could be a start. And I considered having this rotating animation pause occasionally to display the battery level… not sure yet. Or perhaps just stop the animation and switch to a beacon once it hits a low-batt threshold? Dunno yet.

PS - thoughts on how to efficiently do an 8-bit pseudo-random pattern? Bitshifting a predefined pattern? Using int rand() from <stdlib.h>?

113

Pull the code bytes out of flash with an incrementing pointer and output them. When your through, bend it back to the beginning.

114

Here’s a dancing/twinkling version. After seeing it, I’m not sure if it’s my cup of tea, but it was fun to make.

115

It should be pretty simple. The battery status is displayed based on how many LEDs are illuminated. Just rotate that same pattern. They’d still spin around, but the number lit up at any time would indicate the charge level.

The library rand() function would work, and you probably have plenty of space to include it. Or you could roll your own. For example, combine the contents of ROM with a random seed, and do things to make the seed more volatile. I force bits to rotate each time it’s accessed, and I also add real-world entropy to it from each ADC measurement, so it ends up being a true random instead of just pseudo-random. It’s not crypto-grade randomness, but it’s not bad for a cheap chip in a flashlight.

116

Thanks TK. Nice idea on rotating the battery level.

I went ahead a precalculated a ~250 value array of values the randomly switched one bit on, then one bit off. I probably could have just called rand() from the attinys. But for now I think I’ll keep your tip in my back pocket for later.

117

Very creative gc. I could not work out on the video above the dancing light how the voltage was read from the light sequence.

118

Thanks! The voltage readout on that one happens right as it’s turning on. You’ll notice it initially ’spin up” to a certain number of LEDs (1 thru 8) indicating voltage level. It displays that for 3 seconds, then starts a non-informative dance.

I also have it checking the voltage every couple of minutes. If it detects <3.0 volts, it’ll stop dancing and will start flashing a single LED.

119

There are probably several fun things to do with an 8-pixel tail ring like that, especially if it can use the internal resistor to get more than one brightness level. Most of what comes to mind would require a relatively high frame rate though, so probably not ideal for a low-power tailcap. Perhaps it could underclock the MCU to the kHz range and/or run the WDT in sleep mode at a fairly quick rate.

I could see using it to do something similar to candle mode, except it’d also change the position, not just the brightness. Or maybe a couple simultaneous random spinners with erratic motion.

Simply spinning the battery status is probably the most useful mode though.

120

I’m currently running the main clock using the internal ultra low power oscillator, no prescaler (so 32.768 kHz). Using the real time counter interrupt to wake up as needed to move the LEDs.

I haven’t tried adding the internal pull-ups into the mix, but I bet that would work.

Also, it wouldn’t satisfy the anti-PWM crowd, but even with the main clock at 32 kHz, low-resolution PWM could be used for some fading effects. Something like a 16-level (2 kHz) or 8-level (4 kHz) PWM could work, and still be pretty low current draw. Ohh, the possibilities :slight_smile:

121

I know the feeling. I got a keyboard with RGB LEDs under each key, individually addressable. I was pretty excited… I had 64 pixels! So of course I immediately modified the firmware to make it run a physics simulation which responds to keypresses. It simulates the surface of a swimming pool, and each keystroke acts like a raindrop which causes waves.

While eight pixels may not be quite as flexible, it’s still plenty to have a good time. After being limited to just one pixel for so long, eight sounds like a vast playground of possibilities.

122

New “smart” tailcap today. This one is mini for AA sized lights. Swapped out a friend’s Booster Tail for this one since he always uses his Sofirn SF14 with li-ions (with AA/NiMH the flashlight will still work of course, just not the tailcap now). It has 6 LEDs uses them to display battery status.

First battery in the video was at 4.07 V, the second was at 3.55 V.

I currently have the breakdown as such:

  • 6 LEDs: 4.0 V +
  • 5 LEDs: 3.8 - 4.0 V
  • 4 LEDs: 3.6 - 3.8 V
  • 3 LEDs: 3.4 - 3.6 V
  • 2 LEDs: 3.2 - 3.4 V
  • 1 LED: 3.0 - 3.2 V
  • Below 3.0 V, it shuts off
123

This new smart tail cap is a cool idea! reminds me of the new Olight battery status indicators, just in a better location?

124

125

Sweet! Glad to see that they arrived. Everything go smoothly?

126

For my Convoy M1 with L4P driver, yes. Pretty straightforward, just 2 pin to solder between your board and the omten switch and that’s it !
For the Tool AA, unfortunately I didn’t think about it before but I use a Biscotti 5*7135 driver… so the bleeder resistor is tricky to define. I used a 332 (3,3Kohms) but now it’s “next mode” memory…
I have to try a smaller value maybe ? Anyway, I put the tailcap in the lathe at work to accommodate a 14mm clear tailcap :slight_smile: