In this post I have explained a basic Transcranial random noise stimulation (tRNS) circuit diagram which can be implemented externally for stimulating brain cells, resulting in an enhanced performance of the brain.
The design was requested by an avid reader of this blog "Ankita", as given below.
Design Request
I'm interested in building a tRNS device which produces an alternating current with randomly changing frequency and amplitude.
The frequency must remain within 100 to 640 Hz, and the amplitude should vary between -1.5 and 1.5 mA.
My question is: how can I generate this randomly altering current waveform?
Unlike tDCS (transcranial direct current stimulation), which uses a constant current, tRNS employs a dynamic, noise-like current waveform.
This randomness is often achieved through a Gaussian distribution centered around a desired mean intensity.
While the electrode placement and size considerations for tRNS are quite identical to tDCS, the current generating pattern is fundamentally different.
What is tRNS
Transcranial random noise stimulation (tRNS) is a method in which electrical current pulses are sent to the brain without involving surgery.
It works by transmitting a weak electric current with random frequencies through the scalp via two small pads.
This kind of stimulation usually involve a wide range of frequencies, between from 0.1 to 640 Hz.
This can also be applied at slow or fast frequencies, known as lf-tRNS or hf-tRNS (which may usually range between 0.1–100 Hz and 101–640 Hz).
Although this is a modern method, tRNS has become very popular in the last few years.
Scientists across the world have focused on how tRNS affects different brain mechanism like movement, senses, and thinking.
For example, tRNS might seem to enhance brain functioning to visualize things better, recognize faces quickly, and even do fast mathematical calculations.
People who have certain health issues like multiple sclerosis or Parkinson's disease, tRNS could be successful in reducing pain and improving symptoms.
Basically, tRNS, which uses high frequencies, has proved quite beneficial in various situations. For example it makes our senses work better, and might help folks who have certain health challenges.
Circuit Description
The following figure shows the complete circuit diagram of our tRNS device. So I have explained the working of the design through the following explanation:
IC1 is an LM3915 IC which in response to a varying signal at its pin#5 generates a forward reverse sequential logic low across its output pins 1, 18, 17, 16, 15, 14, 13, 12, 11, 10.
Meaning, any varying voltage between 0 and 200 mV at pin#5 of the IC will cause the above output pins to generate a sequentially oscillating low logic.
Since we have 10 outputs for IC1, the input frequency at pin#5 will be divided by 10 across the 10 outputs.
As per the given specifications, the frequency of the tRNS must be between 0.1–100 Hz and 101–640 Hz. However, making a randomly varying frequency looks difficult.
Therefore, in our design we have used an innovative way of implementing this randomly varying frequency, through the IC2 UM66.
The IC2 UM66, is a melody generator IC and is capable of generating a musical frequency ranging from 200 Hz, and 3000 Hz.
Since it is a musical frequency, it has the tendency of randomly varying frequency between 200 Hz and 3000 Hz.
Now, as IC1 is supposed to divide the above frequency by 10, the resulting frequency across the IC1 outputs will be within the range of 20 Hz and 300 Hz. This frequency range seems to be exactly what we want for our tRNS circuit application.
This takes care of the randomly varying frequency specification. There's another parameter that needs to be satisfied for our tRNS circuit design. It is the randomly varying output current.
Implementing the randomly varying output current specification does not look too difficult and becomes possible by using randomly selected resistor values (R5 to R14) across the output pinouts of the IC1. The overall maximum output current range can be also tweaked by adjusting the R3, R4 values.
The above randomly varying frequency and current output is fed to the bases of the transistors T1 and T2.
These transistors suitably amplify the varying signals from IC1 to drive an output transformer TR1 (mistakenly labelled as T1).
The transformer amplifies the varying signal across its secondary winding to generate the intended tRNS output waveform.
Due to randomly switching resistor values at the T1, T2 bases, its collectors feed a randomly varying current amplitude across the secondary winding of the transformer.
How to Build the tRNS Transformer
It is a matter of some experimentation. It may be good to start with 30 + 30 turns for the primary side and 100 turns at the secondary side of the transformer. The wire should be super enameled copper wire, around 0.3 mm thick. The core of the transformer can be any toroidal ferrite ring.
You can experiment with the number of turns to get the most optimal response at the secondary side of the transformer, ensuring that the transistors and the transformer remain cool while operating.
How to Test
The testing procedure does not require too many steps.
After assembling the proposed tRNS circuit over a strip board, recheck all the connections and components polarity to ensure everything's done rightly without any mistakes.
Next, connect an oscilloscope across the secondary side of the transformer and switch ON power through a 12V regulated DC power supply.
You should be able witness a randomly fluctuating waveform on the oscilloscope.
Adjust the 10k preset P1 until the waveform functions optimally without clipping and without saturating the IC1.
You can also set P1 by measuring the peak voltage at pin#5 of IC1 which must not exceed 200 mV.
That's all, your tRNS circuit is now built and tested successfully.
The next step would be to get the circuit verified from a qualified medical engineer and start using it on needy candidates.
Warning: The explained circuit design of Transcranial Random Noise Stimulation (tRNS) has not been practically verified by the author of the post. It is strictly recommended to first verify the circuit working from a medical lab or from a medical professional before using the device practically on patients.
Parts List
- All resistors are 1/4 watt 5% CFR
- R1, R2 = 4.7k
- R3 = 2.7k
- R4 = 390 ohms
- R5 to R14 = select randomly different values between 10k and 100k.
- P1 = 10k prest.
- Semiconductors
- Z1 = 3V 400mW zener diode
- T1, T2 = 2N2907
- IC1 = LM3915
- IC2 = UM66
- Transformer = See Text.
References: Transcranial random noise stimulation (tRNS)
So, to be honest, I need the sine wave generator that I talked about to create a tACS. Therefore, I need, as I said, a sine wave generator that will output a customizable voltage from 9 to 24 volts peak-to-peak and a customizable frequency from 1 to 100 Hz.
I already have an XR2206 generator, but it only produces a 6 volt sine wave. So I’m now thinking about what would be better: make a new sine wave generator, or increase the voltage using a transformer.By the way, speaking of transformers, which one will work for low frequencies:
They are step-down, but if I apply voltage to the secondary winding, can I use them as step-up?
For example, he lowers 220 – 24.If I apply 24 volts to the secondary winding, will I get 200-220 volts on the primary?
And I have a few questions:
1) If you apply less voltage, the transformer will work? For example, if 12, then the output is 100-110?
2) How will lowering the frequency affect its operation? I heard that you need to maintain the V/f ratio for maintain flux.
3) Will there be significant power loss at 4 Hz?
If the transformers that I sent links to are not suitable, please write in more detail about what it should be and,and if possible, name ready-made ones, if you know any on aliexpress.
Hello Nikita,
I have seen the links you provided. The transformers shown in the links will work for you.
In fact any standard iron core step down transformer will work for you.
You can use the XR2206 generator and optimize the output voltage using an iron cored transformer.
Yes, if you apply voltage to the secondary winding, you can use them as step-up.
1) Yes, If you apply less voltage, the transformer will work… For example, if 12, then the output will be 100-110…
2) Yes, you need to maintain the V/f ratio to maintain flux.
3) Yes, there could be significant power loss at 4 Hz, but since your application does not require high power, the losses may be acceptable.
Please provide the output voltage and current details required by you from the transformer, I will try to provide the exact transformer specifications.
I only need to increase the voltage in the range of 2-6 volts to 12-20 volts (preferably at frequencies from 3 to 100 Hz). The minimum current that can be 2-4 mA (can be much more, of course, I think it will not be very convenient to use such thin wires).
I checked the transformer from the second link (220-24 step down). (I note that there may be a copper core there, at least that’s what was written in the title). I used it as a step-up, that is, I applied voltage to the secondary winding. That’s what happened:
(I have two signal generators XR2206 and WSFG-06.)
The XR2206 generated a sine wave at a frequency of 50 Hz and a peak-to-peak amplitude of 5 volts. I connected it to the secondary winding (for 24 volts) At the output of the transformer (the primary winding for 220 volts) I received an almost constant voltage that was slightly lower than from the generator itself (4.60 – 5 volts.) When I decided to lower the frequency and despite the fact that I maintained the V/f ratio, then any voltage disappeared (below 18 hertz).
WSFG-06 behaved strangely. By itself, it produces a voltage of 6.30 volts. When I connected it to a transformer, it began to behave unusually – beeping and blinking. At the output of the transformer, I received a signal of a strange shape, not like a sine wave. Rather, it looked like sharp bursts. The voltage changed and was either more or less than in the original generator signal.
I’m not sure if I can get any other transformers to work with these signal generators. So I would like to see a sine wave generator circuit that could produce a configurable 9-20 volt AC voltage and a configurable frequency of 1-100Hz.
The transformer must be a 100% laminated iron core, no other core will be able to handle low frequencies below 50 Hz, so please make sure to use a perfect iron cored transformer.
For simple sine wave generator circuit, you can refer to the following post:
https://www.homemade-circuits.com/simple-sine-wave-generator-circuits/
Let me know if you have any further questions.
Well, I’m thinking about which of these circuits is more suitable for my idea. Many have a rather small output signal amplitude. Perhaps number 4 would be suitable? What is its output voltage?
I will be glad if you can tell me which of those schemes is more suitable for my project.
The most important requirement is that it can output 12 Vpp, and support low frequencies (up to 100 Hz)
I think for testing purpose, you can try the 6th design Using Two Transistors.
If it works then the parameters can be tweaked as per preference.
https://www.homemade-circuits.com/wp-content/uploads/2022/08/sine-wave-genertaor-circuit-using-two-transistors.jpg
Swagatam, Thank you for this diagram.
What do you think about adding some kind of protection here, such as a filter or fuse, because this is a medical device and safety is very important.
The second thing I wanted to ask is how can the frequency range be made higher? (It would be good to make a range from 100 to 700 Hz, or close to it, because a good effect from TRNS was observed at higher frequencies)
If you know how to do this, it would be better if you show the changes on the diagram and send me the modified diagram.
Thank you Nikita,
The circuit is operated from a low mAh 12V or 9V DC battery which cannot cause any harm to the human body, so fuse may not be necessary for this project. However if you still want to have a fuse in the circuit, you can simply add it in series with the +12V supply line. A 50mA fuse should be good enough.
I am not very sure about the highest frequency range of UM66 IC, it could be higher than 5kHz possibly, in that case the output frequency of the circuit could reach upto 600 Hz.
So I think it would be important to first test the above basic setup and check its performance, and whether it satisfies all the specifications or not.
Once the working of the above basic design is confirmed, then we can replace the UM66 IC with some other programmed IC so that we can get the desired 700 Hz frequency at the output.
Please make sure the person who is testing the circuit is completely well versed with the functioning of the IC LM3915, UM66, the transistors and the transformer, otherwise if something goes wrong troubleshooting might be difficult.
Please let me know if you have any further questions or doubts.