Phototransistors are in effect a bipolar transistor with a transparent enclosure so light can reach the junction of the base and collector. Compared to a photodiode they offer increased gain, but that comes at the cost of a slower response time.

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Photo-Interrupter Usage

One of the projects I am working on requires a number of photo-interrupters to be used. I was wondering if someone could explain how to use them correctly? I was thinking something like this: ...
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2answers
50 views

How ICBO gets amplified to ICEO in BJT when base is open

I have been doing some reading about ICEO and ICBO, but couldn't really understand how ICBO is getting amplified (1+ beta) times to reach ICEO, in the open base condition. This is my understanding ...
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1answer
43 views

ICEO, ICBO physical interpretation in BJT

I am stuck with the equation: ICEO = (1+β) ICBO My questions are: What is the physical interpretation of this equation? Will both the currents exist simultaneously? Are any of the reverse currents ...
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2answers
66 views

How to connect IR sensor ( Infrared detector/receiver )?

Would you give me a hand ? I have an IR sensor with 3 pins. It looks like the one in the picture, and I did not find any datasheet for it on the internet. actually, I have 3 questions : 1- I want ...
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1answer
66 views

Is a DVD sensor a photodiode or an array of them?

Is a DVD sensor just a photodiode or an array of them? I need to know if it is a CMOS with an array of them or just a single sensor.
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1answer
70 views

How do I use a phototransistor for a line follow robot?

I'm building a line follow robot for a competition in 2 months and I'm using Arduino but I have no idea how to find the line (what sensors needed). I did some research and discovered that if I can use ...
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2answers
61 views

Pixel resolution phototransistor array

I would like to ask if anybody knows some technology which is like array of phototransistor with accuracy in mm . Like some display on which I put someting and get by wire data of pixel which are ...
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2answers
85 views

What's the difference between an infra-red and a normal phototransistor?

I was wondering if there is any difference between an infra-red phototransistor and a normal phototransistor. I was also wondering if either of these would be directly compatible with an Arduino? ...
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4answers
65 views

Low-cost long-range movement detection

I have to design a circuit for a device to detect any motion in front of the device up to 2 meters. I have tried with IR reflection sensor, but couldn't achieve the range. Then, I found a circuit on ...
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2answers
39 views

a question about Phototransistor OPB608A

I use a phototransistor OPB608A in my system,shows as below.After capacitor C5, the voltage is 5.5V, that means it will give 5v supply to Pin 1 and Pin 3 of OPB608A, the resistors values are 7.5K and ...
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3answers
138 views

Light activated switch - avoid flicker when turning on

I have a small light bulb (3W LED, E27/110V) that I am controlling using based on ambient brightness (it comes on when it is dark, and goes off when it is light). The circuit uses a BT136 triac, a ...
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2answers
167 views

Are photoresistors reliable for light sensing applications?

I've used photoresistors for hobby projects before, such as this one: http://www.foxytronics.com/learn/electronics/kit-guides/starter-electronics-kit-guide/making-an-led-light-sensor However, now ...
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1answer
71 views

How does a Watt (1mW from a laser) relate to Amps (20mA max current rating for collector of a phototransistor)?

How does a Watt (1mW from a lasermodule) relate to Amps (20mA max current rating for collector of a phototransistor) ? I want to know if the 1mW output from the laser is within or outside the range ...
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2answers
92 views

How to light a LED using photo transistors output?

I built a circuit using RPR220 photo sensor to detect the surface displacement caused on a material when external force is applied. I could see the output on a CRO even when there are minute changes ...
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1answer
71 views

Phototransistor responsivity does not match datasheet?

I am making a basic circuit to test the responsivity of a phototransistor. I made a basic circuit using a phototransistor connected to 5V and a 22kOhm resistor. On the other side of the ...
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1answer
49 views

Detecting and identifying different light sources in arduino?

I want to detect different light sources in arduino. The first Idea about solving this problem came into my mind was to add three light detection sensors (LDR, IR receiver Diode and Photo transistor) ...
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3answers
160 views

Colour Sensor from discrete components?

I am participating in a robotics competition that requires colour detection using discrete components. The aim is to detect red and green lights of traffic signals. I have tried making a sensor ...
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1answer
156 views

Control a 3.6V motor (forward/idle/reverse) using two phototransistors facing a smartphone screen

My purpose is to build a cheap quick-and-dirty "robot" using 2 electrical screwdrivers connected to the wheels and a smartphone to control them. I want to control each motor (forward/idle/reverse) ...
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1answer
138 views

Low-cost phototransistor to MCU interface

The simple way to connect a phototransistor to an MCU is shown in this question. But it requires a Schmitt trigger input which I won't have on my target platform, i.e. either an STM8 at 5V or an ...
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0answers
152 views

Detecting reflected laser beam

I'm trying to do some distance measurement using laser. But most of the articles I read about are concerned with distance of a few meters and went with simple photodiodes I'm trying to achieve a ...
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1answer
85 views

got a too low VCE on a Infrared Phototransistor

I used an Infrared Light Emitting Diode QED123(VF=1.7V) and an Infrared Phototransistor QSD123 in pair. I learnt from QSD123's datasheet that its VCE(SAT) under IC=0.5mA is 0.4V max. But the VCE I ...
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1answer
73 views

How much gain for optical open-air receiver?

I am planning to make an experimental communications system. I will use a high power LED (≈3watts) Amplitude Modulated with a sound signal and eventually Pulse modulated with digital data for the ...
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1answer
244 views

How do I build a light-activated motor? [closed]

I'm trying to build a motor that is activated when light shines on a photoresistor/transistor (can anyone explain the difference?), but I'm totally lost right now. I can only utilize wires, batteries, ...
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1answer
94 views

Identifying and correctly using this component

I have the two components, which are in the picture below. I have a couple of questions. The first one is, how do I make sure that the IR LED detector is working? I tried searching for specs, but the ...
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1answer
176 views

Explaining transistor schematic

I have been away of Electronics Engineering since 2008, it seems I missed a lot of basic concepts. I came across this schematic: I found a weird wiring, the capacitor that is tied to VCC, should be ...
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1answer
349 views

Assistance on values and components, photo-transistor switch for LED array

Yet another photo-switch question. Have done my homework, and searches but most non-specific circuits are beyond my learning curve, time to learn, and available wet-ram. Have a 15 LED array being ...
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1answer
101 views

Detecting Multiple Lasers

I'm looking to design a game where players fire a gun at a target using LASERS or IR. The target only registers a hit when a certain amount of players (say 3) are hitting the target consistantly for ...
16
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7answers
1k views

What was used to detect light before the invention of photodiodes/phototransistors?

Were there technologies before photodiodes/phototransistors or similar semiconductors, which could be used to start or stop machinery based on the amount (or presence/absence) of light falling on ...
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2answers
381 views

RPR-220 photosensor to logic level?

I have RPR-220 reflective photosensor, which transistor's part I connect to 2v via 10 Kohm resistor. Emitter is then connected to the base of a transistor C547B, which for the test setup uses LED + ...
4
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1answer
188 views

Homebrewed phototransistors - unijunction versions

Back in the days, when phototransistors were hard to get (especially in some parts of the world like the communist eastern block), one could brew their own by just filing/sawing off the top of a TO 18 ...
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2answers
213 views

A phototransistor with LED and resistance in emitter

Earlier I used a simple phototransistor arrangement to detect an on/off signal via a laser pulse. I connected the collector to Vcc(5V), and emitter was grounded through a resistance. The base was ...
4
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4answers
380 views

Large Active Area phototransistors? And can solar cells be a replacement

Me and my friends are trying to build a laserharp driven by arduino as a learning exercise. Currently we are using a phototransistor to interrupt the laser light and play music. However the ...
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2answers
387 views

Reading Array of Phototransistors With Raspberry Pi

For a project I'm working on, I need to read the values from a matrix of phototransistors (8x16) into the Raspberry Pi. I'm not exactly sure how to go about doing this, since I know I need to include ...
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2answers
633 views

Connecting phototransistors or photodiodes in series

I am designing a velocity measuring device and want to use 2 strings of 30 photo-transistors in series. The strings are 15mm apart and are illuminated by separate collimated light sources. The ...
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3answers
334 views

Revolutions (pulse) per minute counter circuit?

Does anyone know how to set up a circuit by using counters, decoders, 7 segment displays and a 555 timer to show the revolutions (pulses) per minute from a photo-transistor? I'm doing this as part of ...
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4answers
217 views

Is \$I_e = I_c\$ for phototransistors?

Due to the base current, in a common emitter circuit the emitter current is a bit higher than the collector current: \$ I_e = \dfrac{1+\beta}{\beta} I_c \$ I was wondering how this is for a ...
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1answer
132 views

How to calibrate multiple light sensors at once?

I want to build a simple circuit that by adjusting a Trimpot I can regulate the sensitivity of 4 light sensors such as the QRD1114. I prefer to regulate the gain of the phototransistor instead of ...
2
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1answer
544 views

Programming methods for detecting liquid drops with phototransistor

I have a simple circuit with an LED pointing at a phototransistor. There is a tube in between them that drops of liquid will drip through at random times. I am reading the voltage with an Arduino at ...
2
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1answer
429 views

Phototransistor as a pull-down in digital circuit

I have very little experience with phototransistors. I'm trying to create a circuit that will effectively function as collision detection. I'm using OPB608A which utilizes an NPN transistor. My goal ...
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2answers
2k views

IR LED - phototransistor problem

Pardon my noobness. I'm trying to set up a simple IR LED - Phototransistor pair but am having difficulties. My setup is just as in the following link, except my resistor values are 1K. ...
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1answer
177 views

Low Voltage Photosensor

I'm looking for a photosensor/photo IC part (combination of photodiode, linear amplifier, Schmitt trigger and output transistor) that can be powered with 3.3V. Fairchild QSE256/257/258/259 is almost ...
6
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2answers
299 views

200+ phototransistors and reading them

Im hoping to get some suggestions and ideas on how to read in 200+ phototransistors voltages (0-5) into an ADC? I only need to look at 1 by 1 rather than all at once.
6
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1answer
263 views

Designing a wide-range light detector circuit

I'm looking for a few hints in designing a light detector circuit. Priorities are that the circuit is simple (both as in few parts and as in relatively easy to understand), rather cheap, and can ...
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1answer
312 views

How do i build a laser based tachometer?

I want to build a tachometer that has to be somewhere around 1 meter from the rotating shaft. I'm still to build a prototybe based on IR diode and phototransistor, but I'm afraid, I would get too ...
6
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2answers
948 views

Phototransistor Dark Detector Circuit

So I've decided to make a circuit based on this: I have a few questions. First of all, when the photo-transistor switches off and Q1 switches off, as per the article, what is the voltage going ...
4
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2answers
14k views

Light sensor using Photo Transistor

How can I design a circuit which utilizes a photo-transistor to make a light sensitive switch that is when there is no light in room, the led connected to the photo-transistor lights up and when there ...
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5answers
2k views

Sensor for detecting airsoft bullet

I'm trying to make airsoft chronograph/chronometer (a device that measures airsoft bullet speed). The idea is to measure time in which bullet is traveling from point A to point B, and then I can ...
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1answer
2k views

Simple IR pulse detector with IR phototransistor

I understand the basic circuits used with phototransistors: I believe that this is essentially a voltage divider, commonly used for all sorts of analog sensors. In the left circuit, in the dark, the ...
2
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2answers
477 views

LDR Component Obsolescence

The Light Dependent Resistor (LDR) that I use in MintyTime, Excelitas Tech VT93N2, has been discontinued by the manufacturer. I'm having trouble finding a comparably priced (e.g. < $0.50 @ 100+) ...
3
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3answers
388 views

Remote Control Design

I am want to design a remote control. All I need is the appropriate IR LED and the Receiver to use, that will yield optimal performance. i need real practical experience here. What is the best ...