![]() ![]() Picture 6 Put a finger on the top of the photoreflector to check your pulse Using the same circuit as in Figure 1, place a finger on top of the photoreflector (Figure 4).įigure 4 Photoreflector test circuit diagram So, let’s give this a go using our current circuit. There is a greater amount of hemoglobin in our blood, and thus, by measuring the change in the value, we can apply it as a pulse sensor. When our pulse gets faster, there is more blood flow. Why not apply this further?īy using the infrared absorption of hemoglobin in blood, we are able to measure our pulse. When tracing a line, the photoreflector detects changes in color by detecting changes in the absorption of the emitted LED light by black and white materials. Now, I’d like to try and use the photoreflector in another interesting way. The “if” statement condition needs to be changed for different environments. So, first examine the environment you’re in and change the value accordingly.īy replacing the LED with a motor, or sending the result online through an Ethernet Shield, you can even make a jack-in-the-box that moves when opened, or place it on a door and remotely detect whether it has opened or not there are all kinds of possible applications! You Can Measure Your Pulse? Why? The photoreflector measures a value of 2~5 when the box is closed, but immediately goes over 200 when it is slightly opened hence, the LED is set to light up when the value exceeds 200. Picture 5 The photoreflector is positioned at the box edgeįigure 3 Circuit in which the LED lights up depending on the photoreflector value Picture 4 Depending on whether the box is open or closed, the LED lights up What can we actually do using this property? An example that comes in mind would be using it to check whether drawers, boxes or doors are opened or closed.īy adding a few corrections to the circuit in Figure 1, we arrive at this design, where by putting the photoreflector inside a box, the LED lights up depending on whether the lid is opened or closed. The photoreflector used here has a standard detection range of 1~10mm. If you take a photo using your smartphone camera for example, you will be able to confirm that the infrared LED is emitting a purple color, as seen in Picture 3. ![]() Since it’s infrared LED, you cannot confirm whether the LED is on or not by the naked eye. Picture 3 Infrared LED in the photoreflector By placing a finger closer or further away from the photo-reflector, we can confirm changes in the value shown on the monitor. Once the program is entered into the Arduino, we can have a look at the serial monitor (Figure 2). Picture 2 Test circuit for the photoreflectorįigure 2 Confirmation of the input values on the serial monitor The circuit is shown below in Figure 1.įigure 1 Diagram of the photoreflector test circuit diagram The photo-transistor on the receiver changes its resistance depending on the light it receives. So, we will enter this through the analog-in pin. The transmitter is basically an infrared LED. So, we will construct the circuit in the same way we would do to make an LED light up. Let’s try to measure an input value using the photoreflector. Use a Simple Circuit to Display an Input Value Here, we’ll use a photoreflector with an infrared LED. In electronic kits, it’s also commonly used for robots when running on top of black lines to trace the path of the line. It is often used by measurement machines to detect whether an object is “present” or “not-present”. ![]() The construction is such that light emitted from the transmitter is reflected off an object and received by a phototransistor on the receiver.Ī photoreflector is also known as a “photo-sensor” or “photo interrupter”. Usually, the transmitter of the device is an infrared, blue or ultraviolet LED. Today’s Electronics RecipeĪ photoreflector is a sensor with parts for both sending and receiving. To grasp the general flow of the process, let’s try using a wide range of sensors. Many parts are sold as Shields, but for other parts, we’ll have to build the circuit ourselves. We’ve been making a RC car until now. But from this section onwards, we’re going to use Arduino with various parts and sensors. ![]()
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