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Finished building Low Level Laser Therapy Helmet using #38 3v and #69 5v diodes. The helmet will be used for hair loss prevention. Due to zero knowledge of circuitry, what's the safest and right way to power device? Answered

There are similar projects on this website but all using less diodes. I'm also not convinced that wiring all the diodes in a parallel circuit is the best route. If it is, then great and that will make my life easier.

As you can see in the photos, I've soldered the diodes into bundles. However, each bundle either consists of only 5v or 3v diodes. If I need to desolder anything, so be it. Right now there are bundles of the following:

5v = 20, 15, 22, 12

3v = 9, 9, 9, 11

The diodes were purchased from Amazon and displayed the following specs:


  • Output Power: 5mW
  • Wavelength: 650nm
  • Working Voltage: 3V
  • Operating Current: less than 20 mA
  • Laser Shape: DotWorking
  • temperature: -10 degree~£«40 degree
  • housing: CopperDimensions: 6.5 X 18 mm


  • Output Power: 5mW
  • Wavelength: 650nm
  • Working Voltage: 5V
  • Operating Current: less than 20 mA
  • Laser Shape: DotWorking
  • temperature: -10°C to +40°C
  • Housing material: High quality Copper
  • Dimensions: 6.5 x 18mmWire
  • connection: Red wire connect to Positive, Blue wire connect to Negative

Other purchased materials

2 x 4.8V 700 mAh Rechargeable Ni-Cd Battery

  • Item Name: Ni-Cd Battery
  • Dimension: 2.16 x 1.97 x 0.59 inches
  • Plug: SM 2P Plug
  • Charging time: About 2-3 hours
  • Working time:About 20-30 mins

5 x 4 Cell 4.8V AA Battery Holder W/ JR Style Connector Receiver

Ultimate Goal: Simplify powering of helmet for 20-30 minutes / 3x a week by using on/off switch or plug.

*This is my first time on this website and I apologize if I entered into the wrong category.

THANK YOU in advance to anyone who helps. Greatly appreciated!!


The forums are retiring in 2021 and are now closed for new topics and comments.

1 year ago

Obviously, the laser diodes need to wired in parallel with a 5v power supply.


Best Answer 1 year ago

Don't bother about categories as they don't exists anymore, just a leftover "bug" from a few years ago.

In theory it does not matter how you connect the LED's.
In reality one should try to keep the current on a reasonable level.
Every LED needs a specific voltage and a max of about 15-18mA.
In parallel you might be going a bit short on the expected runtime.
In series the power consumption is significantly lower but it requires really equal LED specs.
Plus of course a suitable resistor for every row of LED's.

In parallel a single resistor per bunch of LED's might still work but it would have to be of bigger size.
At least 250mW for the resistor, which makes it a bit bigger and causes some heat as well.
IMHO and to avoid reworking it all a LED driver might be the best option.
They are constant current power supplies.
Means you set the output voltage you need, like 3 or 5V and the max current - the last should be a fixed value for them anyway.
You can also substitude here with some home made circuits using the LM series of voltage regulators.
Just check for current limiting voltage supplies.


Reply 1 year ago

Thanks for taking the time to reply with a detailed message. I moved forward with using 2 USB power sources, which simplifies the entire process. I've attached some new photos to display what's been done. I figured each 5V from the USB would suffice. The helmet is now used every other day and still works great. Now, the only thing left is to see some hair grow!!

Jack A Lopez
Jack A Lopez

1 year ago

Wow! Nice picture. That's impressive! So you want me to power that thing up and put it on my dome? Ha!


You know, normally laser diodes, or any kind of diodes, want constant current rather than constant voltage.

Although it is different if the things you are calling "laser diodes", are are actually some kind of module intended to be powered by batteries, which are approximately constant voltage sources.

You say you have "zero knowledge of circuitry", yet you seem to grok the difference between series wiring and parallel wiring.

There are two, kind of obvious, corollaries of Kirchhoff's circuit laws,


I am going to quote these corollaries for you right now:

Circuit elements wired in parallel share the same voltage.

Circuit elements wired in series share the same current.

Just meditate on those. I am hopeful these truths will bring you closer to enlightenment.