I'm actually working on a project which is a IRON-MAN Mask with a LED Strips inside his eyes and move detection in his mouth.

Here is what it look like : enter image description here

The problem is that I really don't like the cable in the middle so I'm trying to get rid of it.

Here is the actual circuit :

enter image description here

Since it's in the hallway, It's lightning himself twice a day during 5 seconds each time. I was thinking of putting it on a 3.7 volt battery (18650 with 3000 mAh) and buying a 3.7 -> 12V converter but I'm not sure it's very efficient.. I don't want to recharge it too often (Maximum 1 time every month).

I'm currently using :

  • Arduino nano v3
  • Down converter 12V to 5V
  • RGB strip (6 leds)
  • 12V supply
  • 3 x NPN transistor IRLB8721
  • PIR sensor

But for the next version of it I have :

  • Arduino pro mini 3V3 8mhz
  • 3.7V to 5V converter : Do I really need it ?
  • 2 (or 1) x 18650 Samsung INR18650-30Q 3000mAh battery
  • Charging and battery safe discharge chip 03962A

I did some search so I can save power like : putting into sleep the arduino and waking it up when the PIR sensor is getting a signal, cutting the power led on the board.

So my questions are : Do I buy the 12V converter to power the led or is it useless cause It will drain too much power ? And is it possible to power the 3.3V arduino with a 3.7V battery through the VCC pin (so it's not using the converter on the arduino ex: raw pin) ?

I hope I explain it clearly since I'm French and this is my first post.

Thanks !

  • \$\begingroup\$ Arduino board power supply 3.35 -12 V (3.3V model). What are the characteristics of LED strip? \$\endgroup\$ – AltAir Oct 21 '17 at 17:24
  • \$\begingroup\$ The power is regulated on-board to 3.3 V. It looks like you can supply anything from 3.35 to 12 V \$\endgroup\$ – Blair Fonville Oct 21 '17 at 17:31
  • \$\begingroup\$ The arduino power supply 3.35 -12 V on the raw pin but maybe not directly on the vcc pin isn't it ? And about the LED strip, I really don't know, I took it from this and cut it so I only have 6 LED actually on the piece. \$\endgroup\$ – Simon Menard Oct 21 '17 at 17:35
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    \$\begingroup\$ Be aware that the ATMEGA328P is only rated to operate down to 4.5V @ 16MHz, so you might not get reliable operation with a VCC under that. The simplest solution would be to just use 3 li-on cells and power everything directly from the batteries. \$\endgroup\$ – Dean Franks Oct 21 '17 at 17:49

12v for LED's: You will need to check your datasheet for what you are using.

3.7v li-ion cell direct to VCC: The 18650 cells (li-ion) are actually charged to 4.2v. The 3.7v (sometimes 3.6v) is called it's nominal voltage (like an average but not exactly)and where it will sit at for most of its discharge cycle. But it will deliver 4.2v to VCC, although not for long. So you will have to check the chip type (328 or 328p datasheet?) and see if you're happy with this.

You need to be careful with your charge module. I understand you won't leave it powered up for this project but just incase for the next one. Warning you can trick this module into trickle charging your project. If you leave power into the module and have the battery as backup. Ie I'll power it with mains power and if mains dies battery takes over and later gets charged. If the load is above 100 mA (or 1/10 of CC) the module will never hit cut off current and continue to trickle charge your cell.

This module gave me the biggest learning curve in electronics. It started me on a path to build my own BMS around it, so I could use it (and other types) as a UPS. I still use it and others, damn it really is tiny.

Just learn about li-ion charging and how it operates, then charge a battery and monitor it. Build not a project but an experiment, learn how it works, how it's protection features work and how it fails. Do this with everything you buy not just eBay stuff.

Maybe not the specifics of the answer you wanted but you didn't give enough specifics and I just wanted to warn you about the charge module.

  • \$\begingroup\$ By trickle charge I mean always applies a current to the li-ion cell. \$\endgroup\$ – Tibsy Oct 22 '17 at 23:37
  • \$\begingroup\$ If you use the 18650 cells and charge board. You do not have to make a BMS. You can use an SPDT switch to separate the charge circuit from your load (project). That way when you charge the cell, there is no load that can confuse the module. I would still test it when you first use it. Test what the max current is during the CC stage of charge (this can be changed by changing a resistor on the board. Check your cell datasheet). Check the over voltage protection works as specified ie what voltage does it kick in at. Check the over discharge protection works and cut off current during CV stage. \$\endgroup\$ – Tibsy Oct 23 '17 at 4:50
  • \$\begingroup\$ Hi. First, thanks a lot for answering me. It's very interesting even if it's not exactly what I'm looking for haha. The model is a 3.3v 8mhz ATmega328P-au and for the 12v for LED (6 LEDs) I still don't really know, I didn't buy it and I'm not good in electronics, so I don't really know how to identify what's on it. For the ATmega328P-au I'm trying to find where is the max power it can take. And for the UPS, I knew I shouldn't try to recharge it and use it at the same time and I understand now that you explain ! Thank you for all the details ! \$\endgroup\$ – Simon Menard Oct 23 '17 at 15:35
  • \$\begingroup\$ Could you post some pictures of the LED's, someone might be able to identify it. I'm glad I could help. \$\endgroup\$ – Tibsy Oct 23 '17 at 16:21

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