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.

Filter by
Sorted by
Tagged with
0
votes
0answers
43 views

How to use 4N27 optocoupler?

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 ...
0
votes
2answers
53 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 ...
0
votes
2answers
44 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 ...
1
vote
1answer
48 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 ...
0
votes
1answer
33 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 ...
0
votes
2answers
69 views

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 ...
0
votes
3answers
66 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 ...
1
vote
1answer
85 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, ...
0
votes
4answers
175 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)? ...
2
votes
2answers
113 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 ...
0
votes
1answer
26 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 ...
0
votes
1answer
266 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 ...
1
vote
0answers
181 views

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 ...
0
votes
2answers
126 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 ...
1
vote
1answer
171 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 ...
0
votes
2answers
74 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 ...
0
votes
1answer
37 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 ...
1
vote
1answer
54 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 ...
0
votes
0answers
44 views

How to connect photo-transistors to trigger Arduino event

I'm busy doing my finals project, and I need to have 5 photo-transistors come together on the same pin to trigger an event whenever one of these transistors drops it's voltage because an object is ...
0
votes
3answers
108 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 ...
2
votes
1answer
47 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 ...
0
votes
1answer
168 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 ...
1
vote
2answers
183 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 ...
0
votes
0answers
28 views

Lowest resistor value for enclosed light sensor unit with nearby lighting without losing sensitivity

This is a drawing I made of a light sensor unit I'm creating. Inside of it, I have a circuit board containing 3 7-segment displays and I have two photo-transistors (yellow half-circles in the picture) ...
0
votes
1answer
71 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 ...
1
vote
1answer
57 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 ...
0
votes
3answers
114 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 ...
0
votes
2answers
125 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 ...
0
votes
1answer
59 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 ...
0
votes
1answer
73 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 ...
1
vote
1answer
138 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 ...
0
votes
2answers
58 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 ...
0
votes
2answers
261 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 ...
2
votes
1answer
64 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?
0
votes
0answers
372 views

How to calibrate color sensor to sense RGB colors on the scale of 0-255 if the color source distance varies from 1-25 cm?

I am currently using a TCS3200 RGB color sensor but the sensed values for same color varies with the distance between sensor and color source. How should I calibrate my sensor so as to get values ...
3
votes
3answers
803 views

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 ...
0
votes
1answer
132 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, ...
21
votes
1answer
2k views

Optical audio transmitter can't handle speech

This is a question relating to my project on an optical audio transmitter. I wired up a very simple device in which I use an audio signal transformer (EI14) to modulate the intensity of a laser beam (...
0
votes
1answer
158 views

Diode in 6N138 optocoupler

I'm currently in the process of getting MIDI input to my Raspberry PI through UART, and in order to follow the standards, I should optically insulate the MIDI cable from the RPI by using an ...
1
vote
1answer
113 views

Unusual harmonic data reading from phototransistor in a simple arduino setup

I have a very simple circuit for detecting ambient light readings with an arduino, but I'm noticing a sinusoidal pattern to the readings I'm getting that are hard to pin down the source of. How do I ...
7
votes
1answer
673 views

Why are most IR phototransistors slow?

Most NPN silicon phototransistors that I see (Everlight, Kingbright, etc.) have fairly poor rise and fall times, on the order of 10us. The best one I've seen so far is the QT Brightek QSD8T120B with ...
3
votes
2answers
157 views

Decrease the time it takes to transition from saturation to cutoff of a 2 terminal phototransistor?

Consider a two terminal phototransistor (collector and emitter) that is saturated and the light source is then removed. What can one do to speed the transition from saturation to cutoff ? Edit: ...
3
votes
2answers
210 views

Phototransistor with digital potentiometer

As per the circuit diagram below, I'm trying to use a phototransistor with a digital potentiometer so that the sensitivity can be adjusted. PH_TR connects to an ...
1
vote
4answers
326 views

Optocoupled MOSFET drive

I have a high power 12V rail that I would like to keep separate from the logic supply, and so would like to optocouple the N-MOSFET drive for an external high power LED light. Does this seem like a ...
0
votes
1answer
92 views

Do phototriac optoisolators (e.g. MOC3021) require pulse trains?

I have a project where I need to make a microcontroller trigger an old, non-controlled, camera flash (think of discharging a capacitor through a xenon lamp). First idea was use a transistor-based ...
0
votes
1answer
155 views

How to allow current over a certain voltage

I am new on electronics and i was practicing on transistors. I have a working circuit below. The LDR I use allows current and letting LED smoothly based up to amount of darkness. The Voltage after 2.3 ...
6
votes
2answers
680 views

In a photo diode in which region light should be focused to fall?

In this question correct answer given is option \$(D)\$ that means in a photo diode light should be focused to fall in whole P and N region including the deplection region but when I googled this ...
2
votes
1answer
246 views

Photodiodes over Phototransistors

Current solar panels being manufactured are not considered efficient. I have also read articles saying there is talk or even ongoing research about four P-N layers (i.e: PNPN or vice versa) for solar ...
2
votes
1answer
101 views

Safe to open BJT?

I am experimenting with optically controlling BJTs. In my current project, I take transistors in metal cans and use a diamond saw lubricated with isopropyl alcohol to slice the top off. This generates ...
0
votes
1answer
306 views

phototransistor amplifier quirk

As an amateur to breadboarding I'd been learning about transimpedance amps and photodiodes earlier this year for a project. Eventually I picked up a phototransistor (3DU5C) at a hobby shop, mistaking ...