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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72 views

Calculate pull-up resistor for phototransistors

I have made a sensor which uses six IR phototransistors, three per sensor block, opposite it is a matched IR diode(940nm). This is in turn connected to a MCU. The function of the circuit is an ...
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1answer
40 views

photo-transistor Biasing

How to bias a photo-transistor (the resistance in the collector) given that: Vcc = 5v Vce(sat) = 0.4v Ic(on): min: 0.2 - 1.6 max: 0.6 - 2.4 I'm using ...
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28 views

Equivalent circuit model of phototransistor

I would like to know the equivalent circuit model for a phototransistor. Is there an Ebers-moll model representation? Thanks
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1answer
57 views

Simple and Cheap method to detect object proximity in the dark

I am interested in detecting if an object (e.g. small box made of non-conductive material like plastic/acrylic/wood) is placed on top of a surface (e.g., a table), I don't need to identify the object, ...
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1answer
46 views

Phototransistor resistor value help

I have a rowing machine that I'm trying to replace the computer on. It uses a phototransistor switch to detect flywheel rotation speed. The phototransistor is an Optek OPB365T55. Here is the ...
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2answers
85 views

Optoisolator not turning off

I'm using an optoisolator for high side switching a Nixie tube. For some reason, the optoisolator is not fully turning off, allowing the a very minimal amount of current to flow through the Nixie ...
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1answer
87 views

Load resistor value for phototransistor switch

According to this application note from Fairchild (btw, I find Fairchild's application notes to be of immense value - thanks to all who have taken the time to write one), the load resistor value for a ...
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2answers
96 views

Component to detect the state of an external LED

I need to detect the state of an LED in a machine that I cannot connect to in any electrical way. So I would like to measure the light emitted from this LED. The conditions: The ambient lighting is ...
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1answer
71 views

Phototransistor bandwidth issue

I'm trying to sense IR wave with a phototransistor circuit. The circuit operates well under DC operations (I mean 3V or 0V through inputs). However, if a square wave is supplied from UART input, ...
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1answer
68 views

IR Led & Phototransistor pair bandwidth issue

I'm trying to sense IR wave with a phototransistor circuit. The circuit operates well under DC operations (I mean 3.3V through inputs). However, if a square wave is supplied from UART input, after ...
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0answers
79 views

I guarantee this one will be fun - Need help putting several circuits together into one

So I did my best to annotate the schematic with what I'm trying to do. Where I'm really running into trouble is past the output of the 555. This is basically a control circuit for a camera's ...
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1answer
63 views

Photointerrupter issue

I have circuit with photointerrupter GP1S092HCPIF. The documentation is rather weak and D-shape pin strange but I need a small SMD type. I hopefully identified pins correctly and when soldered on ...
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1answer
80 views

Ambient Light Sensor + Comparator

So I've been looking at options to create a way of controlling whether a flash will fire based on the amount of light in the surrounding environment. Early note: Everything has to be surface mount ...
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0answers
48 views

Information to make a high speed photo detector

I need to make a switch to on and off in nano seconds which is triggered by light source. I considered the following: Using a photo diode coupled to a BJT as a switch- proves to be very slow due to ...
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1answer
96 views

Strategy for up to 40 ADC inputs using alert feature

I'm working on a project where I want to monitor 40 phototransistors (IR breaker beams), but without having to constantly poll the ADCs. Ideally I'd want a digital pin pulled when one of the beams is ...
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1answer
696 views

How to amplify the signal of a TCRT5000 phototransistor

I'm trying to read the IR signal from my Itron C1S Power meter. It has an emitter that lights up for 10 ms every Wh of consumption. This question is based on my prior question: Use a photoresistor ...
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2answers
254 views

How to design a power switching circuit using a photo-interrupter

Okay. I'm completely at a loss here. I was trying to design a switching circuit for a 3A load (Solenoid) using a photo-interrupter. I got to about here: But I have no idea what to look for in my ...
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2answers
272 views

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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1answer
694 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
726 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
491 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
116 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
298 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
148 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
237 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
119 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
66 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
300 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
307 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
87 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
130 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
106 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
60 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
232 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
326 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) ...
2
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1answer
241 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
307 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
152 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
80 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
626 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
102 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
187 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
564 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
116 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
641 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
votes
1answer
210 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
331 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
525 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 ...
3
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2answers
516 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 ...