Simple Hand Grip Strength Tester Circuit

Do you you want to test your grip strength, like a mini hand wrestling match with yourself?

This hand grip tester circuit acts like a fancy meter.

It uses a mix of common electronic parts to measure how hard you squeeze a handle.

The harder you squeeze, the more lights turn on showing off your hand grip power.

Circuit Working:

Parts List:

The diagram below is a staircase type circuit which uses transistors and LEDs to indicate the amount of pressure being applied to the probes.

It works in the following way:

The voltage source 9V is connected to the positive side of all the LEDs.

The bases of the transistors are connected to a voltage divider network made up of resistors.

The resistance of this network is adjusted by the 200k potentiometer.

When pressure is applied to the probes the resistance between the probes decreases.

This allows current to flow through the 470Ω resistors and into the bases of the transistors.

When enough current flows into the base of a transistor it turns on and allows current to flow through the collector and emitter, lighting the LED.

The 1N4148 diode is a protection diode that prevents damage to the circuit in case of reverse voltage.

The 2.2k resistor and 3.3k resistor are biasing resistors for the BC547 transistors.

They set the voltage at the base of the transistors when no current is flowing through the probes.

The 4.7k resistor limits the current that flows through the LED.

The 200k potentiometer allows you to adjust the sensitivity of the circuit.

By turning the potentiometer you can change the resistance of the voltage divider network.

This will change the amount of voltage that is required at the base of a transistor to turn it on.

Overall, this is a simple circuit that can be used to measure grip strength.

The more pressure that is applied to the probes the more LEDs that will light up.

The sensitivity of the circuit can be adjusted by turning the potentiometer.

Formulas:

Typically, a hand grip strength tester circuit uses LEDs to display the grip strength measurement.

Here are some fundamental, pertinent formula for choosing and using components:

Current Collector IC:

The transistors base current IB and current gain β may be used to determine the collector current IC:

I_C ​= β * I_B​

where,

• β for BC547 is normally in the range of 200.

Calculating the Base Resistor:

The base current IB is determined by the base resistor RB, which may be computed using:

R_B​ = V_in​−V_BE​​ / I_B​

where,

• When the base emitter voltage drop (usually around 0.7V for silicon transistors) is represented by VBE, the input voltage is represented by Vin, and the required base current is represented by IB.

Limiting Resistors for Current:

Determine the current limiting resistor CLR for each LED to make sure it works within its safe current range, which is often around 20mA for ordinary 5mm LEDs:

R_LED ​= V_supply​−V_LED​​ / I_LED​

where,

• The supply voltage is represented by Vsupply, the forward voltage drop of the LED is represented by VLED, and the intended LED current is represented by ILED.

Note:

The circuit design of a Hand Grip Strength Tester incorporates LED signaling, transistor switching, resistance measurement, and potentiometer calibration.

The aforementioned equations and recommendations offer a foundation for creating a circuit with the designated parts.

To maximize performance, test the components in real world scenarios and adjust component values according to particular design specifications.

How to build:

To build a simple hand grip strength tester circuit you need to follow the components mentioned in diagram:

Power Supply: 

• Connect the positive terminal of the 9V battery to a common point on the circuit board.

LEDs: 

• Connect the longer leg positive of each LED to the positive terminal from the power supply.
• The shorter leg negative of each LED will be connected to the collector of a separate BC547 transistor Q1 to Q4.

Transistors BC547: 

• Each transistor will have three legs: Collector, Base , and Emitter.
• Connect the collectors to the negative legs of their respective LEDs.
• Connect all the emitter legs together and tie them to ground negative terminal on the circuit board.
• The base of each transistor will be connected to a separate resistor from the voltage divider network.

Voltage Divider Network: 

• This will consist of the 200k potentiometer and multiple resistors likely 3 or 4 based on the number of LEDs.
• One end of the potentiometer connects to the positive terminal of the power supply.
• Multiple resistors will be connected in series between the wiper adjustable contact of the potentiometer and ground.
• Each transistors base resistor will connect to a different point along this chain of resistors created by the potentiometer and fixed resistors.

Probes: 

• The probes will connect between the base of Q5 transistor and positive line.
• When pressure is applied the resistance between the probes decreases allowing current to flow through this resistor and into the base of the transistors.

Diode 1N4148: 

• This is typically placed in parallel with the reverse polarity of the diode banded side towards the negative terminal across the power supply connection to prevent damage from accidentally reversing the battery connection.

Resistors other than voltage divider: 

• The 2.2k and 3.3k resistors likely connect between the base of each transistor and the voltage divider network biasing the transistors when no current flows through the probes.
• The 4.7k resistors likely connect in series with each LED to limit current flow and protect them.

Important Note:

• This is a general guideline and the specific connections might vary depending on the exact circuit design.
• Please go through the schematic diagram for this specific circuit it will provide the most accurate connection instructions.
• For safety reasons it’s important to double check the connections before powering on the circuit.

Conclusion:

To conclude, a hand grip strength tester circuit is a basic tool that can provide a general indication of grip strength.

It is a good option for hobbyists or for non critical monitoring but for precise measurements or medical applications a digital dynamometer is recommended.

References:

Hand-grip strength test using the hand-grip dynamometer 

Grip strength