6 Flashing LED's with variable speed in a specific range.

Thread Starter


Joined Jan 22, 2020
I would like to make a simple mind machine.
It consists of a modified pair of glasses with three red LED's on each side, set close to closed eyelids which flash concurrently at a specific frequency which is controlled by the user using a knob on the front of the machine.

It will have 6 red LED bulbs.
They flash concurrently and their frequency can be controlled by a variable resistor.
When the resistor is at its lowest setting they should flash at around 1Hz, when it is at its highest setting it should be at about 15Hz. This doesn't need to be too exact.
The LED's need to be as bright as possible but also need to be less than a centimeter from a closed eyelid, so they should not produce significant heat.

I have very little experience with circuit design. I have found a number of flashing LED circuits on the internet but I don't know how to modify them to get the specific frequency range I require. It has been a while since I have had to use my math skills, so working out the values of the resistors and capacitor is difficult for me.

Any help in designing this project would be appreciated.


Joined Jan 29, 2010
hi Neil,
Welcome to AAC,
Do you have more information on the type of LED's you plan to use.
Colour, Voltage/Current rating etc.

BTW: I guess you are aware that flashing lights around 15Hz,16Hz can induce nausea, vertigo in some people.???


Joined Sep 24, 2015
Another question to be considered - - - At any given frequency - do you want the LED's to be on and off equal duration? Meaning regardless of the frequency, should they be on for 50% of the frequency and off for the other 50%? Or do you want a flash of light that is on for, oh, for the sake of example lets say "20 mS (milliseconds)"?

In other words:
- on - off - - - - - - - - on - off - - - - - - - - on - off - - - - - - - - on ?
- - on - - off - - on - - off - - on - - off - - on - - off - - on - - off - - ?

Both are possible. You can even have them on for most of the time with only a blink off - similar to that of a pumpkin with blinking LED's to simulate the blink of an eye.
It has been a while since I have had to use my math skills, so working out the values of the resistors and capacitor is difficult for me.
Me too. If you have an excel spreadsheet you can construct a page where you input the resistance (in ohms, not K ohms) and capacitance (in farads, not micro farads or any other smaller measure) and the page will show you the frequency results. You can hone in on the frequency you want and figure out what variable resistance is needed to give you the range of adjustability. Using a 555 timer chip you can control the duration of light on to light off timing as well.


Joined Sep 24, 2015
I had a similar idea many years ago. Only instead of using a set frequency of flash rate I thought of using an audio source to flash the lights and couple it with headphones. The goal was to listen to text being read aloud with the lights giving secondary input stimulating the brain to remember facts as read more betterer. (yes, I spelled it that way).

One of the "Back To The Future" movies, Doc Brown used a sleep inducer that used flashing lights that flashed at the same rate as the brain's alpha waves to induce sleep. Pretty interesting theory put forth by Hollywood. I don't know if such a thing would actually work. Would be interesting to try it out. Maybe even use an audio frequency to match.

Thread Starter


Joined Jan 22, 2020
I have to do a bit of research into the types of LED. Six of them, they should all be red, bright as possible but without producing much heat, and I would prefer to be able to power them with a battery but that is not completely necessary. Suggestions appreciated.

On-off flashing where they are off as long as they are on.

While I was searching I think I found some websites that have calculators that do the same thing as your spreadsheet. Though I am still not %100 sure how to use them in this context. Total noob here.

What Doc Brown was using in BTTF was a legit piece of technology that totally works. Look up brainwave entrainment.

I have been using one for years. Look up mindroid on google play. Mindroid allows you to program different frequencies for different states of mind.

I use it to help me fall asleep and to get me into a relaxed state while listening to music. It also produces groovy visuals.

I want to build myself a simple one because the mindroid app requires a pair of glasses with it which are expensive and badly made, I have been constantly repairing and messing with them for years to keep them going, but now they have stopped working reliably.

Thanks for your help guys.