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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73 views

MIDI to Arduino with a 4N38 Optocoupler

I ordered a set of optocouplers the other day and was excited when they finally came in. Unfortunately, I've having a bit of trouble getting them to work. Simple on/off tasks work fine but when I ...
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2answers
55 views

Opto-coupler base connection speed influence

I am using a 4N25 opto-coupler for 5kHz to 10kHz application. In some datasheets the turn on and turn off times are mentioned to be 3us. I am wondering if this opto-coupler is suitable for my ...
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19 views

how to connect light transistor to serial out

I want to be able to communicate between two computers through a laser. On the laser's side, I have a raspberry pi turning it on and off. On the receiving side, I want to somehow connect a ...
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1answer
61 views

Are IR phototransistors always dark, are IR LEDs always clear?

I've been working through the "Electronic Circuits for the Evil Genius" guide and someone bought me a components kit for the guide specifically. I already have some phototransistors where the plastic ...
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2answers
192 views

isolated input circuit to check regular switch or photo-transistor

I am trying to develop a circuit that is compatible with a regular switch (push, reed, other) and also a phototransistor. The application is pinball, where there are any number of switches and IR ...
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40 views

AC Coupling Capacitor Value

How to Calculate the value of the AC coupling Capacitor?
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45 views

Photocoupler interface

I found a CNA1011K photocoupler laying around and I wish to try it out. Could someone explain what the parameters from the datasheet mean and how to use them for particular circuit parameters? LED ...
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2answers
94 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
47 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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32 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
71 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
72 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
89 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
219 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
113 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
90 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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2answers
111 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
81 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
71 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
89 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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1answer
66 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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2answers
1k 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
329 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
337 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
888 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
1k 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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795 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
134 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
395 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
176 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
294 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
137 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
84 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
335 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
342 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
90 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
136 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
115 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
64 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
248 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 ...
0
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1answer
384 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
266 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
351 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
180 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
82 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
782 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
106 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
188 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
625 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 ...