Simple Electronic Muscle Stimulation Circuit

An EMS circuit is a machine that uses electrical zaps to make muscles move.

It is built with various electronic parts like timers, signal makers, boosters and sticky pads.

The circuit creates controlled electrical tingles that travel through sticky pads placed on your skin over your muscles.

These tingles are like the messages your brain sends to your muscles, making them tighten up and loosen up.

Circuit Working:

Parts List:

Comprising two units, the system includes a muscle stimulator and a timer.

An Electronic Muscle Stimulation EMS Circuit, depicted in diagram, utilizes IC 7555 configured as an astable multivibrator generating pulses at approximately 80Hz.

By adjusting potentiometer VR1 users can regulate the intensity of current sensed at the electrodes.

The brightness of LED1 corresponds to the pulse amplitude.

To increase intensity, one can substitute the 1.8kΩ resistor with a higher value up to 10k.

X1, a small mains transformer, features a 220V primary and a 12V, 100/150mA secondary.

It should be connected in reverse with the secondary winding linked to the collector of T2 and ground, and the primary winding connected to the output electrodes.

The output voltage reaches around 60V, but the output current is minimal posing no risk of electric shock.

Electrodes, typically small metallic plates measuring approximately 2.5×2.5 cm² are attached using flexible wires soldered to the devices output.

Before application to the body the metal electrodes should be wiped with a damp cloth.

Upon affixing the electrodes to the body secured with elastic bands on velcro straps activate the circuit by toggling switch S1 and gradually adjust the intensity control preset VR1 until a slight tingling sensation is felt.

Formula and Calculations:

The IC 555 oscillates between high and low states in astable mode, producing an output of square waves.

Resistors and capacitors that are external can be used to modify the square waves frequency and duty cycle.

The following formula can be used to roughly compute the frequency (f) and duty cycle D in an astable multivibrator circuit that uses the 555 IC:

Frequency (f):

The values of the resistors R1, R2 and the capacitor C connected to the 555 define the frequency of oscillation in the astable mode.

f = 1.44​ (R1+2 * R2) * C

here,

• R1 is the resistor that connects Pin 7 (the discharge pin) to Vcc.
• R2 is the resistor that connects the threshold pin 6 to the discharge pin 7.
• C is the capacitor attached to the pins 6 and 2, which are the threshold and trigger pins, and the discharge pin 7.

Duty Cycle D:

The following formula may be used to approximate the duty cycle, which is the ratio of the outputs high time to the entire period:

D = (R1 + R2)​ / (R1 + 2R2)

This formula provides you with the proportion of the oscillation period that the output is high.

f = 1.44​ (R1 + 2R2) * C

f = 1.44​ / [180+(2 * 1.8)] * 0.0000001

= 78431Hz

= 78.431kHz

So, the frequency f of oscillation is approximately 78.431 kHz

Duty Cycle Calculation:

D = (R1 + R2)​ / (R1 + 2R2)

D= (180+1.8​) / [180+(2*1.8)]

D = 0.99

So, the duty cycle Dis approximately 99%

Using these calculations, which are based on the values of the external resistors and capacitor used for the circuit, one can easily estimate the frequency and duty cycle of the output waveform produced by the IC 555 operating in astable mode.

You may modify the output frequency and duty cycle to meet the needs of your electronic muscle stimulation (EMS) application by adjusting R1, R2 and C.

How to Build:

To build the electronic muscle stimulator circuit following are the assembling steps mentioned:

Circuit Assembly:

• Begin by placing the IC 7555 onto the circuit board.
• Ensure proper orientation.
• Connect the 1.8k resistor between the appropriate pins of the IC 7555.
• Optionally, replace this resistor with a higher value resistor for increased intensity.
• Install the potentiometer VR1 and adjust its position as desired.
• Connect LED1 to the circuit, ensuring the correct polarity.
• Connect the transistor T2 to the circuit according to the schematic.
• Wire the transformer X1 to the circuit ensuring the primary and secondary connections are correct.
• Connect the electrodes to the circuit using flexible wires.
• Solder the wires securely.
• Clean the electrodes with a damp cloth before use.
• Attach the circuit board and components to a suitable housing or enclosure.
• Install the switch S1 in a convenient location on the housing.
• Affix elastic bands to the housing allowing for the attachment of the electrodes to the body.
• Ensure all connections are secure and insulated to prevent short circuits.
• Test the circuit to ensure proper functionality and adjust the intensity using VR1 as needed.

Usage:

• Apply the electrodes to the desired area of the body using elastic bands and velcro straps.
• Activate the circuit by flipping switch S1.
• Gradually adjust the intensity using VR1 until a slight tingling sensation is felt.
• Use the device for muscle stimulation as needed following appropriate safety precautions.

Note:

• Be cautious when working with electricity and soldering irons.
• Follow safety guidelines and ensure proper insulation and grounding to prevent electric shocks or injuries.
• If unsure, seek assistance from someone experienced in electronics assembly.

Conclusion:

To conclude, An Electronic Muscle Stimulation EMS Circuit provide a non invasive and potentially effective way to stimulate muscles for various therapeutic and fitness purposes.

However, it is important to use them safely and under appropriate guidance especially concerning intensity levels and electrode placement to avoid any adverse effects.

References:

Electrical muscle stimulation

Development of a Circuit for Functional Electrical Stimulation