A Laser Guided Swimming Lane Aid

People with visual impairments can face difficulties staying within their designated lanes in a swimming pool for several reasons:

1. Lack of Visual Cues: Swimming lanes are typically separated by visible lane ropes or markers on the pool floor. People with visual impairments cannot rely on these visual cues to stay in their lanes.

2. Spatial Awareness: Swimming requires a good sense of spatial awareness to stay within the confines of a lane. Visual cues help sighted swimmers maintain their orientation, but individuals with visual impairments must rely on other senses and strategies.

3. Navigational Challenges: In addition to staying within a lane, swimmers with visual impairments need to navigate the pool safely to avoid collisions with lane ropes, other swimmers, or pool walls.

4. Orientation: Swimming in a straight line can be challenging when a swimmer cannot see their surroundings. Without visual references, it's easy to veer off course and move toward the center or sides of the pool.

Solution

Developing a laser sheet-based guidance system for swimmers with visual impairments to remain within their lanes holds great potential. This innovative system can offer either haptic or auditory cues to assist swimmers in maintaining their orientation while in the pool.

The setup requires the installation of two line lasers (parallel beams) in the pool, emitting red laser light within the 650nm to 668nm wavelength range. To make this system work, swimmers will wear two specialized devices equipped with photodiodes, a fresnel lens, and a basic microcontroller unit (MCU) capable of providing haptic feedback.

Here's how it functions: As the swimmer approaches the laser line or sheet, the fresnel lens focuses the laser light onto the photodiode. A plastic color filter ensures that the photodiode only reacts to the laser light of a specific wavelength. When the photodiode detects this light, the wearable device immediately delivers haptic feedback to the swimmer, serving as a tactile indicator to help them stay within their lane effectively.

This technology represents an exciting innovation that can significantly enhance the swimming experience for individuals with visual impairments, offering them a reliable means of maintaining their course and orientation in the pool.

Why Fresnel Lens and Filter?

Fresnel Lens:

A typical Fresnel lens is a flat, transparent sheet with a series of ridges or concentric rings on one side. These ridges are designed to refract (bend) light in a specific way to converge it at a focal point. The ridges are shaped like segments of a conventional curved lens, but they are "flattened out" to fit on the flat surface of the lens.

By choosing an appropriate Fresnel lens, the sensor's coverage area and sensitivity can be tailored to the application's specific needs. A Fresnel lens from a PIR sensor is used in this project to focus all the scattered light from the laser to the photodiode.

Optical Filter:

Longpass filters are optical devices designed to transmit a specific range of wavelengths of light (or a band of frequencies) while blocking or significantly attenuating light outside that range. These filters are used in various optical and photonic applications for a range of purposes.

A 632nm long pass filter is used to filter out all the light below 632nm and let pass above 632nm. This makes the wavelength of red laser (665nm) at its peak transmission. The below image compares the image with and without a filter.

Build:

Step 1: Assembling Electronics

The PCB consists of an AD8615 OPAMP, Seeedstudio Xiao (any variant with battery charging pads compatible) and a haptic motor. Once the PCB is populated, it is tested for the response of ambient light.

Step 2: Adjusting the Resistance

The transimpedance amplifier is the most common configuration for interfacing a photodiode with an op-amp. It converts the photocurrent generated by the photodiode into a voltage output. The basic circuit consists of the photodiode connected in reverse bias with the op-amp in a non-inverting configuration. The output from the OPAMP is adjusted by changing R1 in the above schematic. To change the resistance, it is advised to shine the line laser on the fresnel lens from a distance > 2 meters. This should be done with the filter present in the photodiode.

Step 3: 3D Printing and Assembly

The files for the casing are provided below. Once the parts are printed and post-processed (removing support and filing them), the electronics are to be assembled on the casing. Before assembling the top part, the filter needs to be installed on top of the photodiode as shown in the below image.

Step 4: Firmware

int opampPin = A1;    // the input pin from OPAMP
int statPin = D3;    // select the output pin for the LED
int motorPin = D10;    // select the output pin for the haptic motor

int sensorValue = 0;  // variable to store the value coming from the OPAMP

void setup() 
{
pinMode(opampPin, INPUT);
pinMode(statPin, OUTPUT);
pinMode(motorPin, OUTPUT);
Serial.begin(115200);
}

void loop() 
{
  // read the value from the sensor:
  sensorValue = analogRead(opampPin);    
  Serial.println(sensorValue);            
  if(sensorValue > 3046) //Adjust this value based on the response of photodiode and the laser used.
  {
  digitalWrite(motorPin, HIGH);
  digitalWrite(statPin, HIGH);  
  delay(1000);
  }
  digitalWrite(motorPin, LOW);
  digitalWrite(statPin, LOW);  
}

Power:

The device uses a small 400mAh battery from Adafruit. One of the biggest advantages of using a Xiao than its form factor is that it has a built-in battery charger and can run on a battery. The hardware is also having a voltage divider circuit to monitor the battery voltage for user alerts.

Further Work:

The project entails extensive field testing, particularly in swimming pools, and includes multiple iterations throughout its development. Below listed are some of the planned experiments & iterations to be performed.

• Installing Line lasers in the swimming pools.
• Choosing the right power for the laser depending upon the pool length.
• Making silicon caps for the wearable device.

Feel free to contact me for further questions.

Happy Making!