# LED lighting for use in miniature tanks

Novice, built a model for a popular wargame.

I built a modular tank using magnets for multiple variants from 1 kit.

I hope to add some LEDs (max of 20 3V) & fibre optic lights on the vehicle and fibre optics for laser sights or panel lights etc.

For the fiber optics, I plan to make sealed boxes/packets with a grommet in each to allow a 3mm LED to be fitted, 1 for RGBW colours with the fiber optic cables for each colour ending inside the box/ packet. All sealed up and blacked out to stop light leakage to the main body. Probably heat shink or acrylic resin seal. I'll need 2 of these 1 for main hull lights and one for the turret for the sights.

Been looking at a 4056 USB charging board to be hidden behind a panel as a way to charge the battery pack in the main body of the vehicle battery pack.

For the battery pack, I hope to be able recycle 18650 batteries from an old laptop battery pack for the project.

I don't know where to start, how to work out what battery power I'll need, if I can step it up if needs be. I've read a badly fitted LED can burn a system out. Should I find something to protect the circuit?

Is it worthwhile buying pre soldered LEDs with resistors and leads already done?

I read that LEDs are best wired in series, I'll hope to use the magnets to transfer power between modules either to charge individual battry set ups (enough room depending on the size of the battery required, I have several batteries from rechargeable pocket items e.g. ear buds battery pack/storage) or simply to continue power to the lights running through the section (1 mag + ve, 1 mag -ve ) The space is approx 30mm x 70mm x 160mm of the top of my head, may vary 5 mm in some cases, I'll clarify if required. The LEDs are going to be fitted about the body.

The battery pack, charger, a fiber optics box, and power transfer (hopefully magnets where possible to maintain the modular set up of the model) will be in the base, the rest will involve wiring the LEDs to the various modules. Anyway thats the brief outline, please ask if I'm unclear.

• Hi fren! Is this your first electronics project and do you already know how to program microcontrollers? Oh wait is this a non motorized model tank so you just need to know how to select, power and wire LEDs and battery circuits? – K H May 1 at 22:34
• Can you try to boil this down to an actual specific question? And please add a schematic. – Elliot Alderson May 1 at 22:36
• Can you drill a hole in the LED ? to epoxy a plastic fiber optic line or fishing clear line. If can be a 3mm or 5mm LED. Black heat shrink works well,. Using a 3.7V Battery you can use an efficient 5mm LED at 10mA with 0.7V/70 Ohm in series for each LED. – Tony Stewart EE75 May 1 at 22:44
• Also remember a diagram is worth ten good descriptions and a thousand average descriptions, so maybe add a diagram of what you're planning. If you want some form of wireless charging, you should look up the measurements on DIY Qi charger pads as you might find them too big to put more than one into a project. – K H May 1 at 22:46
• Ah, you seem to be asking too many questions at a time, and I lost count how many, when I finished reading the third paragraph of your question. Let me suggest to eat the big elephant byte by byte, in three byes. And I would suggest to begin with the LED part. / To continue, – tlfong01 May 2 at 2:48

1. There are many types of LED and LED strips. For newbies, I would recommend to start off with 12V LED strips (Ref 6), which is the easiest to DIY. For ninjas, I would recommend WS2812 RGB LEDS, which is a bit tricky to handle.

1. To DIY 12V LED strips, first thing first is to study the inner circuitry and workings. I would recommend to read the tutorials by WaveFormLighting (Ref 8). It is only after we know what is going on inside the strip, then we can do fancy things such as dimming, using tricks such as PWM (Pulse Width Modulation).

1. Talk is cheap, let us now study the schematic (Wait a second. Have you already read the tutorials by Components 101 and WaveformLighting? :)) and see how we can light up the real thing: the 12V LED strip, and later dim it.

3.1 Now I have cut a 3 LED segment from my half a meter long green strip, and now going to solder wires and test it with 12VDC.

3.2 I found the green LED strip is too bright at 12V. I tried to lower power supply to 7V and found the LED dimmed to more pleasing to my eyes. I know a better way to dim is to use PWM, which the trick I will use pretty soon.

3.2.1 12V full brightness


3.2.2 7V dimming


1. Testing R, G, B, Y strips together

So I have separately test 4 R, G, B, Y LED strips. The OP can use 3 LED strips or 6 LED strips, or even longer (but in multiples of 3 LEDs). The strips have 3M adhesive tapes at the back, so it is easy to just peel off the protective surface and stick the sticky strip to any smooth surface. It took me less than three minutes to stick four strips on a proto board, and use 12V to light up them all at once, as shown below.

5. Dimming LED strips using PWM

1. I am thinking of using 7/8 channel ULN2003/2803 500mA sink drivers to switch the power on/off the LED strip.

2. Then I can use a cheapy 555 timer module to generate square pulses of difference duty cycles, as PWM signals to input to the ULN2003/ULN2803 drivers to DIM the LED strips.

Note: Using ULN2803 8-channel driver and NE555 timer, we can test PWM dimming offline, during prototyping stage, without using Arduino or Rpi. I think this offline testing approach is more time efficient for newbies, who are slow in programming.

/ to continue, ...

References

Appendices

Appendix A - WS2812 RGB LEDs

Appendix B - 1W 350mA LED, without heat sink

Appendix C - 1W LED with heat sink