What’s the Frequency Kenneth?

5 11 2014

(An idea for an electromechanical 40 Hz tACS generator stage)


This is based around the science of using an AC electric motor as a dynamo or generator in the same way how turbines work in modern power stations to create electricity at 50 or 60 cycles per second or hertz.

A power station

However I thought I would devise a quick experiment using a spare AC synchronised motor used in a central heating system to test my theory of trying to create a clean sine wave like in the recent Voss lucid dream lab study; nothing else.

The 5 rpm brushless motor (with integral gearbox) itself is designed to run at 230 volts AC at a frequency of 50 Hz with a power output of 6 watts.

synchronised electric motor

I simply hooked the two terminals to my oscilloscope via the probe, turned the motor spindle slowly clockwise initially where I checked the on-screen trace.

To my surprise I got a clean looking, virtually pure sine wave with the voltage and frequency rising proportional to the speed.

At 40 Hz I noted the voltage equalled about 8.5 volts peak to peak, although I couldn’t keep the output voltage or frequency constant due to the irregular input speed!


Oscilloscope and sine wave trace from generator

However I did not check the output load where I could have connected a light bulb and measured the current flowing through it.



I’m tempted to hook this up to a mini water wheel, an exercise bike, or even have a steam powered generator via a kettle during, and after a wake back to bed session.

Maybe by adding another gearbox along with a flywheel like in one of those wind-up radios, then I could convert it into a self-powered tACS oscillator stage.

On a slightly serious and more practical note, the constant input speed needed to maintain the 40 Hz output frequency could be delivered by a good quality DC motor with a cog system to turn the spindle at the correct speed which would have to be regulated and overcome the initial starting torque of the AC motor.


Electronically speaking then something like a Wien bridge, or similar type oscillator would be a totally better and much more practical option to produce some sort of sine wave-type output; preferably over a pulse generator like an IC 555 which would create more harmonics.

A clean 40 Hz sinusoidal wave audio file of a short timed duration could also be converted to an electrical signal and processed further provided it had no noise.

This mp3 file could be incorporated for playing on LucidScribe for example, with the signal taken via the audio out socket on the laptop computer (on batteries only) before being fed through opto-isolators for extra safety and further processing.


Ursula and Ariel cartoon

Is this the correct montage Ursula?

I have obviously not taken into account that a viable, safe working system for tACS would need further amplification and signal processing stages, including, filtering, current limiting and protection, isolation and matching etc. along with electrodes that suited your system and you.

Not to mention the thorough testing needed!


Disclaimer: Do not connect directly to your brain or body!

AC high voltage motors can be extremely dangerous to you and your equipment. Certain electrical motors and types may also be unsuitable for testing and use, either due to high rpm, voltage, phase, frequency, current and size.


This project information is shown for education purposes only.




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