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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46 views

Calculating range of between LED and phototransistor

I would like to tell briefly about circuit. When LED is ligth(on),it will trigger ptohotransistor for work. I wonder that between these two component of range is important. Is there any calculate ...
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4answers
77 views

What's the difference in a digital optocoupler and a non digital

I'm looking at 2 different optocouplers.The Avaago ACPL-K44T and the ACPL-227. The ACPL-K43T states that it's a digital opto-coupler while Avago ACPL-227 doesn't. Schematically, they're a bit ...
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0answers
45 views

Phototransistor modulation and 50Hz interference

I've got an LED being modulated at 1kHz. This then points towards a phototransistor (LPT80A) which is wired up in a common emitter configuration with a collector resistor of 1k. The output of this ...
0
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1answer
53 views

What is an ideal setup for detecting objects moving through an enclosed space? [duplicate]

I'm trying to create an ammo counter for an airsoft gun. I'm going to control it with an attiny series MCU and i want to detect the projectiles exiting the barrel using a light based sensor. Now that'...
0
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2answers
99 views

What is a typical response time for a photodiode/phototransistor?

I'm trying to get an ATtiny26l MCU to detect a very short signal produced by a IR led + detector couple (I don't know if it's a photodiode or a phototransistor buit i think it's a diode) and the setup ...
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0answers
69 views

Pulse sensor: Choosing the right resistor for the phototransistor

I want to use specifically the SFH 309 NPN phototransistor in order to create a pulse sensor that works as seen below: The IR diode emits IR light to the fingertip from the one side and on the ...
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2answers
80 views

D Flip-Flop as pulse detector

Background For a while now I've been trying to come up with a simple module to handle modulated light detection for part of a laser trip sensor. Initial attempts I wanted to use a dual op-amp as an ...
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0answers
58 views

Opamp isolation buffer behind phototransistor

Part of a PCB I designed looks like this: Simple phototransistor with a resistor to measure the voltage over. More light => more voltage over the resistor. However, the circuit behind the output ...
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1answer
140 views

When wiring IR Phototransistor, why is a pulldown resistor needed?

My phototransistor looks like the one here, wired like this: I don't know the exact model or anything like that. It came in an Arduino kit and was labeled "flame sensor". I used an arduino to ...
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1answer
41 views

Dark current versus temperature in phototransistors

Typically dark current rises quite rapidly with respect to temperature. If I have two of the same type of phototransistor, how well is the rise in dark current matched between them?
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3answers
81 views

Phototransistor with virtual ground opamp design

I am setting up a high sensitivity light detection circuit and came across this thread just a bit ago: Phototransistor transimpedance amplifier Within it was a response with this image: My ...
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1answer
149 views

Is there a digital input that registers light? / Can only ADC pins register signals from an LDR?

I have been building a traffic light over the past year as a GCSE project. Initially, what was unique about it was that, the pedestrian interface would light up when it was dark outside. Subsequently, ...
0
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1answer
154 views

How do I calculate maximum frequency supported by an optocoupler say for example PC817 and what factors it depends on? [closed]

I am currently working on isolating SPI bus.The SCLK for my non isolated version of design is 5MHz .How do I calculate whether the optocoupler is suitable for operation at this frequency of operation....
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3answers
77 views

Surface-Mount Prototyping (AXL 335 & SFH 7050)

I'm working on a senior project and I'm having some trouble prototyping with surface mount components. I know you can find SMT adapters out there for most SMT chips and components, but I've been ...
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2answers
146 views

A protecting circuit using GPIO of the BeagleBone (Black or Green)

I'm really trying to develop a cape since I need to use 7-8 GPIO-Pins of my BBB Green and Black as Output. I'm too afraid to destroy the board somehow, so I was thinking to implement a solution which ...
0
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1answer
74 views

Light Detector/Identifier circuit using photodiodes

I'm currently completing my final year project and am currently stuck going round in circles as how to complete it. To summarise: I need to design a circuit which is capable of IDENTIFYING a light ...
0
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1answer
166 views

normally open or normally closed OptoMos

In the following OptoMos datasheet the OptoMos is defined as Normally closed, when there is no input the output is closed. But in other OptoMos like the SFH618A-2 i can't find if the OptoMos is NO or ...
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1answer
152 views

Designing photogate for Raspberry Pi 2

Please help: I am building a photogate. I was looking for help in building a circuit for the Raspberry Pi 2. A little background: I am still a highschool grade 12 student! and I have a basic ...
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1answer
119 views

Will this phototransistor circuit work?

I'm building an 8 stage coil gun for a physics project, and I want to verify this circuit as I've never used a phototransistor before and I'm still pretty new to mosfets. Here is a schematic: The ...
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2answers
137 views

Why won't my phototransistor interrupt my microcontroller?

I bought a couple of phototransistors. They all have one lead shorter than the other. I assume that, like normal diodes, this means that the longer lead goes to V+ and the short end goes to GND. I ...
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1answer
82 views

How to use same 'input' for two circuits

First of all, please excuse my complete lack of knowledge in electronics :) Let's start with a little bit of context. I am trying to modify a machine that already uses a photo-interrupter to measure ...
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2answers
75 views

Designs for a 3-lead phototransistor?

I'm working on a primarily optical project, but I need to get a simple circuit working. I'm working with an npn 3-lead phototransistor (datasheet). I was trying to get the current from the ...
2
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2answers
99 views

Photogate IR LED or laser

Hi I am trying to build simple photo gate to measure speed of incoming ball. I decided I will use one photo gate with high frequency. Because ball is much smaller then the box, which is comming in, ...
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1answer
95 views

Can anybody identify this part - I think it is a phototransistor of some kind?

I suspect this is some kind of phototransistor, except it has three leads instead of two. It has no part number anywhere on it. Is anyone familiar with it?
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1answer
44 views

Phototransistor Values

So currently I am using a phototranssitor to detect light from several IR LEDS; however, I am having some trouble. I am currently using the right side of the circuit in the picture half way down the ...
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2answers
232 views

Opto-isolator output from collector vs. emitter

I have an Isocom ISQ2X quad opto-isolator (datasheet) that I will use to drive a logic input. The opto-isolator's simplified model given by the datasheet is pictured below. The transistor base pin is ...
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1answer
136 views

How to Compute bias Resistor for phototransistor Value?

I want to use this phototransistor in an Arduino project: https://www.kingbrightusa.com/images/catalog/spec/WP3DP3BT.pdf I calculated the value of the phototransistor bias Resistor (R1) by the ...
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1answer
775 views

Use an LED as an input to a phototransistor in LT-SPICE [closed]

As a part of a project I am producing a light gate incorporating a photo-transistor and an LED. The design features feedback between the the LED and photo-transistor, so it would be useful to be able ...
9
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1answer
353 views

What are the differences between optoisolator output styles?

Digikey lists optoisolators with several output types: Darlington Darlington with base Photo FET Photovoltaic Photovoltaic, linearized Transistor Transistor, with base What are the differences ...
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2answers
493 views

What is RadioShack 276-0326?

It says it is an ambient light sensor, but is it a phototransistor? Something else? It has Vcc and Vout pins. Bonus points if you include a data sheet.
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2answers
864 views

Understanding the CNY70 Reflective Optical Sensor

As far as I know, TM4C123 LaunchPad safely accepts voltages values up to 3.3V . I got a CNY70 reflective optical sensor and want to connect it to one of the analog input ports safely as in the ...
2
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2answers
775 views

how to get the RGB value of a color using phototransistor or photodiode?

I'm making a color analyzer which can measure Red, Green, and Blue portions of a color (ex: 128,255,0).I'm not supposed to use pre-made color sensors and need 1% ACCURACY. I used three LEDs - R,B &...
2
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1answer
279 views

how to measure RBG values of a color using phototransistor

I am developing a circuit which can measure RGB values of a given color. I have used LED to transmit light and reflected light is filtered by 3 R, G, B filter papers. Earlier I used LDR and found that ...
0
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2answers
221 views

is it a photodiode or a phototransistor?

I have been working on a circuit which involves a photosensitive element soldered on a PCB. I am confused whether it is a photodiode or a phototransistor. Is there any means by which I can figure out ...
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2answers
277 views

Simple Phototransistor Motion Detector

I am trying to make a simple motion detector for objects within a few feet in a very small footprint with minimal parts. I don't need to know much info about the motion just simply if there was motion ...
2
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2answers
959 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 ...
1
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2answers
292 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 circuit'...
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1answer
258 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 ...
1
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2answers
320 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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2answers
69 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 ...
0
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2answers
548 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 ...
1
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1answer
132 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 LTR-...
0
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1answer
125 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, ...
1
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1answer
192 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 ...
1
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2answers
130 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 ...
0
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1answer
372 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 ...
3
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2answers
279 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 ...
1
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1answer
189 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, ...
0
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2answers
272 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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1answer
153 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 ...