Hello, please read disclaimer below. A Tens machine is used to provide a drug-free way of removing pain from your body. TENS stands for Transcutaneous Electrical Nerve Stimulation
.With off the shelf part, the 555 timer is very small, about a quarter of the size of your fingernail. There are two types of Tens machines. High-Frequency Tens that use frequencies in the range of 80 to 100 Hz. This blocks the pain impulses going to the brain. or a Low-frequency Tens uses frequencies from 2 to 4 Hz. This will help the body produce its own endorphins and increase local blood flow to relieve pain ( this can last for hours).

Square waves are universally encountered in digital switching circuits and are naturally generated by binary (two-level) logic devices. They are used as timing references or "clock signals", because their fast transitions are suitable for triggering synchronous logic circuits at precisely determined intervals. However, as the frequency-domain graph shows, square waves contain a wide range of harmonics.

WARNING: The device mentioned here is just for learning purposes and is not designed for human use or above the neck or for individuals with a pacemaker or other heart defects. This device should not be used by pregnant humans.

The “Square wave” permits the frequencies to penetrate the body more efficiently at any given Khz output. Square waves are considered the superior “frequency to wave” output for any Frequency generator device.

What is the 555 Timer IC Chip?

One would place the 555 timers in the center of the project and then build around it . Looking at internet Diagrams will show you how the Pins from 1 to 8 on the 555 Timer are connected up. Each pin of the 555 is numbered from 1 to 8 .

How the Square Wave Is Generated

The ratio of the high period to the total period of a square wave is called the duty cycle. A true square wave has a 50% duty cycle - equal high and low periods. The average level of a square wave is also given by the duty cycle, so by varying the on and off periods and then averaging, it is possible to represent any value between the two limiting levels. This is the basis of pulse width modulation.

Parts List I found online for a Low-Frequency Tens Machine ( Generating the Square Wave ). Not for Human use.

(1) 205 K ohm Resistor
(2) 233 ohm Resistor
(3) 5.01 M ohm Resistor
(4) 10 nF Capacitor
(5) 47 nF Capacitor
(6) 555 Timer IC
(7) 28.81ma Light Emitting Diode
(8) Rocker Switch
(9) 9 volt Battery
(10) Thin wire
(11) Solder ( and a soldering iron ) or small breadboard
(12) Conducting pads

Low Frequency Tens Machine Diagram ( Wave: Asymmetrical )

Once all the parts are together, they should be placed out and wired up shown in the diagram. You could either solder them together or connect them using a very small breadboard. If you find it difficult to see the values in the diagram, these are what they are :

(1) 205 K ohm Resistor
(2) 233 ohm Resistor
(3) 5.01 M ohm Resistor
(4) 10 nF Capacitor
(5) 47 nF Capacitor
(6) 555 Timer IC

When you wire up the Light Emitting Diode, the resistor should be connected to the ( a or + ) Cathode ( the Long Lead ) side of the Light Emitting Diode. The short side is connected to the negative or ground side.

High Frequency Tens Machine ( Wave: Asymmetrical )

To change your device into a High-Frequency Tens Machine, you only need to replace 2 resistors.
Replace the 205 K ohm resistor with a 6.8 K ohm resistor
and Replace the 5.01 M ohm resistor with a 167 K ohm resistor

(1) 6.8 K ohm Resistor
(2) 167 K ohm Resistor

The two red conducting pads shown in the diagram are the silver Foil covered pads to be placed on the body. Although you will not cause any damage to the unit, the +/- conducting pads should be kept apart from each other.

Experimenting

To change your device for treatment, you only need to replace 2 resistors and 1 Capacitor.

Replace the 6.8 K ohm resistor with a 9.6 K ohm resistor.
Replace the 47 nF Capacitor with 100 pF Capacitor
andReplace the 167 K ohm resistor with a 236 K ohm resistor

Parts List
(1) 9.6 K ohm Resistor
(2) 236 K ohm Resistor
(3) 100 pF Capacitor

This would give an out put of 30 k Hz , to potentially kill parasites in the body, raise the ph to remove acidic environments in the blood . Allow healing Lymphocytes to do their job properly . The Square wave formula for all square waves is below . You can also visit this website for more information about what your device can achieve . Although their device is out of range of the Low Frequency TENS that you will be building .

This means it has 8 different pins, each of which have different functions for the IC. The chart below gives the identities of each of the pins and what function they play in a circuit.\

Pin 1 connects the 555 timer chip to ground.
Pin 2 is the trigger pin. It works like a starter pistol to start the 555 timer running. The trigger is an active low trigger, which means that the timer starts when voltage on pin 2 drops to below 1/3 of the supply voltage. When the 555 is triggered via pin 2, the output on pin 3 goes high.
Pin 3 is the output pin. 555 timer's output is digital in nature. It is either high or low. The output is either low, which is very close to 0V, or high, which is close to the supply voltage that's placed on pin 8. The output pin is where you would connect the load that you want the 555 timer to power. This may be an LED, in the case of a 555 timer LED flasher circuit.
Pin 4 is the reset pin. This pin can be used to restart the 555 timer's timing operation.
This is an active low input, just like the trigger input. Thus, pin 4 must be connected to the supply voltage of the 555 timer to operate. If it is momentarily grounded, the 555 timer's operation is interrupted and won't start again until it's triggered again via pin 2.
Pin 5 is the control pin. In most 555 timer circuits, this pin is simply connected to ground, usually through a small capacitor, about 0.01 µF capacitor. This capacitor serves to level out any fluctuations in the power supply voltage that might affect the operation of the timer.
Some circuits (though rare) do use a resistor between the control pin and Vcc to apply a small voltage to pin 5. This voltage alters the threshold voltage, which in turn changes the timing interval. Most circuits do not use this capability, though.
Pin 6 is the threshold pin. The purpose of this pin is to monitor the voltage across the capacitor that's discharged by pin 7. When this voltage reaches 2/3 of the supply voltage (Vcc), the timing cycle ends, and the output on pin 3 goes low.
Pin 7 is the discharge pin. This pin is used to discharge an external capacitor that works in conjunction with a resistor to control the timing interval. In most circuits, pin 7 is connected to the supply voltage through a resistor and to ground through a capacitor.
Pin 8 is connected to the positive power supply voltage.
555 timer ICs need DC voltage in order to operate. This is the pin that connects to the DC voltage to power the 555 chip.
The voltage must be at least 4.5V and no greater than 15V. It's common to run 555 timer circuits using 4 AA or AAA batteries for 6V or a single 9V battery.
Connecting the pins in different ways, we can put the 555 timer in astable mode, bistable mode, or monostable mode.
The 555 timer can be used for basic timing functions, create warning lights that flash on and off, produce musical notes of varying frequencies, and even control the control position of a servo motor.

About the Author - Ryan DeWitt

I'm here to help. I'm a hacker. So my story of why I learned electronics. Since 2015 this hearing brain condition of tinnitus (notice I did not say my) sound level has gone from 8/10 to sustained 1/10 (almost silence if I wasn't listening for it) This success has happened for many reasons and personal interventions that I share for free on this channel and a book Hacking Tinnitus. As a few other makers do on (YouTube, Reddit, TinntusTalk, Tintushub, and Wikipedia) I learned a lot online and in Design Engineering school and now pay it forward to teach people how to switch devices with Arduino-based microcomputer electronics. And you can learn too. For Clarification, I do not make nor share plans on making a human use Tens Unit. Why would we do that?? Why reinvent the wheel when you can just switch the electric output with strategic timing using the code you come up with. For my one-on-one teaching design workshops, we offer a Non-Medical sound switch and a vibration switch; you can check out these on my website and schedule a one-on-one Zoom meeting. The parts are 3D Printed, and the electronics can all be bought over the shelf. I first designed these for exhibit design and entertainment. Musically controlled fountains. I do not sell a B-Modal device to treat any medical condition. My Story - As many are, I'm very interested in any possibilities of multi-modal or Bi-Modal Stimulation therapies., neuromodulation, bio-hacking, and Neuroplasticity technologies to treat tinnitus. I'm truly excited but concerned about cost and availability. Because I have a few product engineering and maker skills, I've decided to investigate my solution while a US Commercial Product is available. My goals are these. Encourage the emergence of US Commerical products for those with patents, discover new related hybrid therapy avenues, and help move this technology forward with self-research from a tinnitus patient perspective, not as a Corporation. I want to share (for hope) is after using my first prototype (temporarily) I have noticed a decrease in my Tinnitus volume; however, I have not sustained use for 60 days. I will see if using it longer sustains that decrease in volume. Now that I have a portable unit, I plan to use it on a schedule and document my progress; however, to be crystal clear, I'm not selling a Medical Device. Disclaimer- Any File or part or process mentioned in this video (i.e. sound switch, vibration switch, or any electronic feedback device, etc.) or any product mentioned does not involve human use, it simply serves as a learning tool for inventors and is not intended to diagnose, treat, cure or prevent any human disease. Any statements made on sites or videos by other inventors, bloggers, or YouTubers regarding the mentioned parts have not yet been evaluated by the United States Food and Drug Administration. Or, to put it another way, you may use the mentioned (educational knowledge) at your own risk. You assume all liability for any misuse, injury, or unlikely death. This product is not intended to diagnose, treat, cure or prevent any disease . My YouTube channel is operated under Context Communications LLC (dba hackLAB) . Always wear hearing, eye protection, or a helmet if necessary. Love ya. Publically Available References NIH Grant Study - Bi-modal stimulation in the treatment of tinnitus: a study protocol for an exploratory trial to optimize stimulation parameters and patient subtyping https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5665258/ Auditory-somatosensory bimodal stimulation desynchronizes brain circuitry to reduce tinnitus in guinea pigs and humans. https://www.ncbi.nlm.nih.gov/pubmed/29298868 Noninvasive Bimodal Neuromodulation for the Treatment of Tinnitus: Protocol for a Second Large-Scale Double-Blind Randomized Clinical Trial to Optimize Stimulation Parameters. https://www.ncbi.nlm.nih.gov/pubmed/31573942 Tinnitus Treatment Using Noninvasive and Minimally Invasive Electric Stimulation: Experimental Design and Feasibility https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6330726/ Bimodal stimulus timing-dependent plasticity in the primary auditory cortex is altered after noise exposure with and without tinnitus. https://www.ncbi.nlm.nih.gov/pubmed/26289461

How does a Tens Unit Work - 555