Questions tagged [phototransistor]

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 at the cost of a slower response time.

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42 views

How do these phototransistors circuits work?

In the figure 1, When there is insufficient light, the darlington transistor is biased on, keeping the relay energized. When there is sufficient light, phototransistor FT turns on; I imagine this ...
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66 views

Vs1838B break beam problem

So im using ESP32 to output 38khz 40% duty cycle wave to ir led and connecting a vs1838b on the other side. The vs1838b works as it outputs LOW when i send a signal from my remote. Anyways, after the ...
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How to simulate a phototransistor in a circuit, prefereably in ltSpice?

I copied a circuit from a working pcb, which is detecting small IR intensity changes. I like to simulate it in ltSpice but I dont know how?! notes on circuit: the transistor is bc847, op amp is lm324, ...
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Why would you use a feedback resistor on a logic buffer?

Please excuse my poorly drawn photo-interrupter circuit. It is used for external home sensing where a flag will interrupt the light source, turning off the phototransistor. I'm just curious as to ...
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139 views

Switching a 5V power relay with optocoupler

I have looked at the schematics of a few 5V power relays and noticed different designs. Some use just a transistor to draw the higher current to switch the coil and some use optocoupler (surge ...
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Will a 950 nm IR emitter work with a 870 nm phototransistor?

I'm planning to build a simple IR light barrier across a distance of 15 mm. I plan to use this receiver with this emitter. The reason is to have some SMD PNP capable components. The emitter and ...
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124 views

Why are capacitors used parallel to transistors

In the circuit attached. There are two capacitors. One is parallel to "PWR LED". Although I understand it delays the turning on and off of the LED, why would you need that? Also, the other capacitor ...
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35 views

Can reverse breakdown voltage be used to simulate lifetime aging of phototransistors?

As phototransistors age, their responsivity to light decreases (a fixed amount of light generate less photocurrent). To simulate long-term aging of phototransistors in a short period of time, one can ...
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173 views

How to build fast visible light detector

I need a circuit which can detect flickering of light too fast. I have Digital LDR Module which is too slow can I replace LDR with L14G2. Digital LDR Module - Digital LDR Circuit - Can we ...
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107 views

Phototransistor amplifier

In the following picture: I have screenshotted a picture of the front end of a phototransistor receiver circuit from Electronic Gadgets for the Evil Genius. It appears to be a phototransistor-based ...
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70 views

Phototransistor Datasheet Confusion

I am going through this datasheet of a photo-transistor from Fairchild Semiconductor. Problem-1: I cant figure out the gain of the photo-transistor (like in other normal BJTs). There is something ...
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Vishay TCST2300 Testing (Transmissive Optical Sensor with Phototransistor Outpu)

New here and relatively simple question for those experienced with electronics. Unfortunately, my experience is limited and I'm confused by the TCST2300 datasheet information. Specifically, I'm ...
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127 views

What component does this symbol represent?

Can anybody please tell me the name of the component represented by this symbol (encircled in picture.)
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How to detect IR pulse using phototransistor and voltage comparator (subtracting constant light)

I want to detect an IR pulse with a phototransistor. I did the following schematic, using the voltage comparator LM339: The problem is that this will work if in the dark, but if there is some light, ...
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53 views

What is the difference between the order LP filter + Op-Amp and Op-Amp + LP filter in practice?

I have issues explaining what really happens on my circuit. I'm trying to make a cardiofrequencemeter with a white LED and a phototransistor. Basically I light the phototransistor, and measure the ...
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Transimpedance AMP, Active HPF, phototransistor

So this is the part where I would like the phototransistor (TEMT6000X01) to be able to clearly capture an LED with a frequency flashing on and off at 1kHz. So what I have here is a transimpedance ...
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205 views

How to use 4N27 optocoupler? [duplicate]

I was wondering why the 4N27 optocoupler has a pin for base of the phototransistor - and of course how to connect it. I've usually dealt with PC817 optocouplers and connected them according to the ...
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114 views

Dual slope edge detection for a phototransistor

I want to detect sudden changes in light level using a phototransistor. The goal is to transmit information optically using the timing of the transitions, ideally using an LCD screen. LCD transitions ...
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158 views

SFH3310 Phototransistor read ADC value

I want to sense brightness via an OSRAM SFH3310 phototransistor by using an ADC (Vref 3.3V - teensy 3.1). I understand that I need a voltage divider to get a good ADC reading. In the past I simply ...
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68 views

Circuit topology name and function for PNP transistor in light barrier circuit

I have seen this rather simple circuit for end position detection of a DC motor drive mechanism. An infrared LED (V402) and a phototransistor (V401) are used as a light barrier. Can someone give me a ...
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176 views

IR Sensor Replacement

I am currently designing a circuit, where output is switched on and off as obstacle passes IR (Infrared) beam, produced by IR LED and received by IR sensor (IR photo-transistor). The problem is that ...
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Do the photocouplers on this module have any possible purpose? [duplicate]

I purchased a number of these relay module boards off AliExpress. They consist of the following 16x relays, 12 volt coils A LM2596 setup as a buck converter 2x ULN2803A darlington arrays 16x 817C ...
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223 views

identify infrared receiver

My CD player's infrared receiver for its remote control has failed. (The remote still works with a friend's identical player.) I'd like to buy a replacement receiver and solder it in. How do I ...
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1answer
227 views

Phototransistor relay circuit

I don't quite understand this type of circuit: When light strikes Q1 (phototransistor), if the light is intense enough, Q1 is turned on, then current flows into the base of Q2 which also turns Q2 on, ...
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1k views

Can an optocoupler be used as a switch [closed]

I am trying to replace a analog switch (the switch is a momentary button in a low current DC situation) with optocoupler. Is it possible to use an optocoupler as a switch (i.e. just on/off)? ...
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358 views

Very low current (<10 microamps) darkness detector circuit that turns off in light

I've made a device that lights an LED at a very low current (<10 microamps) as a very dim indicator for use in the dark. At its simplest, the circuit is a 3V coin battery + resistor (300K-1M ...
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76 views

Phototransistor and Photodiodes capacitances when some in an array sense light

I'm using phototransistors to sense low speed data (about 7 bits a second). With one phototransistor and a 300K resistor, I found my sweet spot and can transmit correct data with lazer. I find if the ...
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718 views

Can you connect multiple photodiodes in parallel and treat it as one?

Im working on an IR sensor based off of the Texas Instr. particle sensor (TIDA-00378). They use just one photodiode in their design. I would like to use multiple photodiodes, lined up with multiple ...
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Optocoupler 24V input misbehaving

I have an optocoupler circuit that is used to accept 24V input (100 ms pulses) and interfaced to a microcontroller. The schematic is as follows: Opto: BL817C or TLP621. TLP621 datasheet As per my ...
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273 views

Optocoupler to drive LEDs (maybe with transistor)

I wonder if there is some simple solution to drive LEDs powered from single rectified voltage. Assume AC is 220 V, each LEDs is 3.0 - 3.2 V 150 mA. I reckon series connection made it simpler but not ...
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472 views

How to find polarity of photo interrupter

I have scavenged some photo interrupters from multiple printers but I am trying to figure out the polarity and the voltage. I've tried searching up photo interrupter polarity but couldn't find ...
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99 views

Why did Adafruit pick a 10K resistor for this phototransistor breakout?

Adafruit has an ALS-PT19 Analog Light Sensor Breakout. It looks like it has a 10K resistor on it: The ALS-PT19 datasheet says that resistor is to convert the output current of the transistor to ...
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54 views

How do I determine the capacitor to use when converting current to voltage?

I'm trying to figure out how to use an ALS-PT19-315C/L177/TR8 phototransistor (or something like it). The datasheet has this sample circuit for converting current to voltage so that I can measure it ...
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1answer
58 views

How do current and voltage relate to load?

I think I've lost the plot somewhat on how current and voltage relate to the load in a circuit and I'm hoping for some really basic level clarification. In fact, I'm not really sure how to ask the ...
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128 views

Can a series resistor be used to limit the power consumption of a phototransistor?

I’m hoping to use several QRD1113 IR proximity sensors in a device, and they work well but have higher power consumption than I would like. I’ve tested many other ones, but I haven’t found another ...
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73 views

Multiple phototransistors one OR output

I am trying to wrap my mind around a design for a long light sensor bar. This is actually a laser sensor that needs to sense a moving laser beam continuously over a certain distance. I would need this ...
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347 views

Photodiode temperature compensation

The goal is to design a circuit that can accurately measure light intensity with little temperature dependency. Common application uses photodiodes to do so. Photodiodes can be measured either in ...
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2answers
446 views

Do NPN and PNP phototransistor switch complementarily?

I am trying to understand whether there is a difference in the switching characteristics of NPN and PNP phototransistors. My understanding is: NPN: current flows when light is incident, no current ...
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101 views

Sensor range and speed based on resistor

I have 4 of these sensor circuits and can't quite figure out the optimal resistor value to use. Here's what I assume (which somewhere I may be wrong): The datasheet for the IC states leakage current ...
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1answer
80 views

Can sending correct data via UART qualify as valid manchester encoding?

I'm currently in the process of having a laser beam detected by the phototransistor. While the parts in themselves work, I want to detect when the beam has been detected. I understand that a 38Khz ...
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126 views

Transistors with different loads in parallel

My circuit roughly looks like this: I want to send a signal to uC and turn on a LED when there is light shining on phototransistor Q3. Currently I'm using stm32f4 (discovery board) as a signal ...
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202 views

Add tilt switch to this photodiode circuit

I'd like to take this phototransistor switch circuit: And add a tilt-ball or similar switch in series. That switch needs to be heavily debounced, so that it stays "switched" more or less for several ...
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1answer
80 views

calculating maximum sense speed of amplified phototransistor circuit

I made the following photo-transistor circuit to sense light with the exact parts shown. Resistors are 5% tolerance 1/4 watt. The circuit does work, but what I would like to know is how do I calculate ...
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1answer
104 views

LED as transmitter and photodetector in the same circuit?

As in this answer I plan to use a 5V neopixel RGB LED as both transmitter and receiver to transmit information between ATMega328 boards via fibre optic cable. (This is the Forrest Mimms strategy, for ...
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1answer
212 views

Replacing obsolete photodarlington with phototransistor

I've got an old circuit design I need to replicate, function wise, to fit into an existing larger design. Logic I can usually handle, anything with transistors starts to get me lost. My strength is ...
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60 views

covering sides of LEDS without adding heat

I'm doing a project in which a 5mm LED is near a 5mm phototransistor. There are times in which the sensor must pick up external light even with the LED on. I understand one option is to turn the LEDs ...
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387 views

Photo-diode for a high-frequency tachometer

I intend to build a tachometer, which is capable of detecting rotations up to 1kHz (60 000 RPM). From the Internet I know that this is possible to do with a magnet and a Hall detector. However, I ...
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71 views

Is the LED-like device in the front of an Arduino flame sensor a photo transistor?

This is a common Arduino flame sensor found in the Elegoo 37 sensors kit V2. Is the led in front of it a photo transitor?
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How to transmit data with a laser beam? [closed]

I am working on a project about data transmission with lasers. The project is very young so I can modify my current planned setup if necessary. This is the actual planned setup: Every raspberryPi ...
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1answer
182 views

Saturating BJT with phototransistor

simulate this circuit – Schematic created using CircuitLab I'm trying to get a phototransistor to saturate a BJT so that when a small amount of light is present, the BJT is on. At the moment, ...