Idea: Flashlight with battery level indicator

[PeterFH]

Hello!
For the past few weeks i have been thinking about trying to build my own custom flashlight, a small compact one that i can keep in my pocket all day.
Mostly to get one feature i would love to have, a battery level indicator.
I would like to know how many hours the lamp will be able to run.

The electronics are not a problem, i have build way more complicated things but one part that gives me a headache is, the human interface, the "display".

The light needs to have a few brightness levels, i would like to make it continously variable which presents a problem with the display since the remaining battery life needs to be calculated with the current brightness, a simple bar graph is not that helpfull in that case.
I need a solution that is nice to look at, durable and is not too cumbersome.

My first idea was a cheap chinese OLED, one of the small 128x64 pixel SSD1306 displays, but that is a bit flashy but i got a few of those in my parts drawer.

A small LED matrix, 5x20 pixel fits the idea nicely but takes up a lot of space.

A LED bar graph provides not too much data and is not scaleable.

A regular backlit COG LCD is fairly thick and big as well.

A seven segment LCD needs a bit of additional circuitry, i could not find a decent one that fit my needs.

A really neat idea i had, takes up a lot of room, one or two of these small chinese linear stepper motors with a needle display and scale.

The rough idea is to run it of a sigle Li* cell and make it re-chargeable with a micro usb connector and put a fuel gauge ic in it.
I have all the parts i need left over from other projects, so i am a bit set with a few components that i want to use.
It is all SSOP/TQFN/SON with 0805 passives, so the circuit needs quite a bit or board space since i only can do double layer boards.

Who made it this far, thank you for reading, i hope you got some feedback for me!

Greetings,
Peter

 

[mrheosuper]

A small compact edc=> you should use led indicator, a 10 micro led would be perfect

Led matrix is not good for this project, since oled 0.96 has a lot of pixel, but not takes too much space, and just only need 4 wires to communicate with it(include the power wire)
The led 7 segment can't display as much infomation as oled, and need at least 4-7 wire to use( if you use ic drive)
So, i would prefer to oled 0.96, small but powerfull, u can draw everything with it

 

[DIWdiver]

Hi, and welcome to the forum!

It's pretty obvious you are okay with using a microprocessor, so...

If you can solder TQFNs, you should be able to solder 0603 or even 0402 size passives and SMT LEDs. You could build your own bargraph, with 25-30 segments per inch, or even a 2 or 3-digit 7-segment display in a pretty compact size. A 2-digit display would only take 9 pins on the micro and 7 resistors if you can get away with a few mA per segment.

 

[PeterFH]

Hi, and welcome to the forum!

It's pretty obvious you are okay with using a microprocessor, so...

Yea, im quite used to working with them, the driver i want to use requires one anyway since it has a one wire interface and uses analog diming and no PWM.

[/QUOTE]
If you can solder TQFNs, you should be able to solder 0603 or even 0402 size passives and SMT LEDs. You could build your own bargraph, with 25-30 segments per inch, or even a 2 or 3-digit 7-segment display in a pretty compact size. A 2-digit display would only take 9 pins on the micro and 7 resistors if you can get away with a few mA per segment.[/QUOTE]

LEDs in 0402 i can solder, i think. Mostly i stick to 0805 since my whole parts stock is that size.

You just gave me a great idea, i do not know why i have not thought about it sooner.
One of these small led bubble displays, i should get a few of them either used or NOS on ebay.
They are fairly small and with 4 digits i can more then adequately display the runtime in minutes and hours.
If not i can just cobble together a tiny 7 segment out of discrete LEDs with a small pcb, that is even smaller.

Thank you
I am a bit low on IO pins, but i could just use a WS2803 to drive the display, that does not take up too much space, still got a few of them.

Greetings,
Peter

 

[PeterFH]

So, i would prefer to oled 0.96, small but powerfull, u can draw everything with it

Yea, i got one of them sitting on my desk, they are really awesome for this sort of thing.
It just does not feel like it belongs, too modern.

But... mhm...
I could put a decal over the screen and simulate a tiny 7 segment like that.
That might work, thanks!

Greetings,
Peter

 

[StarHalo]

Bluetooth transmitter to phone app, skip the flashlight interface entirely..

 

[mrheosuper]

nitecore tm36 has an oled display, so, oled is a good way to display info
and since you has few IO Pin, i2c is a best interface( just use 2 wire)