Questions tagged [optoelectronics]
Components, circuits, or systems that convert between electrical and optical (light) energy.
269 questions
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How can I stop this part oscillating - HFBR-2555AFZ
hopefully I can pose this question well.
I have a fiberoptic communications circuit as part of a larger device which I designed which has worked really well with HFBR-2505AZ, but unfortunately I can ...
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Photodiode reverse light current question
I am looking at a photodiode BPV10NF and it says the typical reverse light current is 55 μA.
In the lab, I have found that the light current keeps increasing with light intensity well past 300 μA when ...
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Saturating BJT in emitter follower
Can we saturate the BJT in emitter follower configuration by increasing base current? If yes, what happens in the process? How does increase in collector current decrease \$V_{CE}\$ when there is no ...
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Emitter Follower - Normal BJT vs Phototransistor
Here is the circuit of normal BJT in emitter follower configuration.
I understand that when conducting, $$V_e = V_b - 0.7$$
In the above case, \$V_e = 1.33V\$
Now, consider an opto coupler circuit as ...
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Arduino -> PC847 optocoupler ->WS2812b RGB LED circuit isn't working
I must be doing something dumb here as my circuit tests fine yet I can't control the 5mm LED(not a strip of them).
I have a simple 1 second on/off pulse on the input pin 22. I measured pin 16 on the ...
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HCPL2531 offset voltage status at opto output
I am testing in a panel with very high motor noise. I want to pass the encoder data through the opto. When I apply the following scheme, my inputs and outputs are as I want.
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Then I ...
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Should decoupling be made before PC817 opto-coupler?
I am having trouble with "duplicated" signals when my microprocessor receives digital input. I think that the lack of proper decoupling could cause the issue, but I don't have the knowledge ...
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PCB design references and roadmap
I am a fresh electrical engineering graduate. I want to learn PCB design and I don't know where to start. Most courses on the internet explain basic electronics taught in university, but nothing ...
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What is LED starter?
What exactly is LED starter?
The producers ship it with only a vague explanation that it is needed to replace the original fluorescent tube starter when replacing the fluorescent tube with its LED ...
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How can I design a heart-pulse-sensing circuit using a BPW34 photodiode?
I tried to build this circuit that I found online:
After I built it, I don't think it was working properly. I tried measuring the op amp output with a multimeter, it was very small (below 0.300v) and ...
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High Voltage Switching using OPTO MOSFET [closed]
I have made a circuit using OPTO MOSFET for turning electro magnet ON/Off.
The issue is when opto MOSFET turns on the current limiting resistor 2.7 kΩ heats up. It's a 2 W resistor. Opto MOSFET is ...
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Confusion regarding driving a MOSFET through optoisolator
I am currently developing a circuit board for a control chassis, that will control various light outputs depending on what inputs are active, no fast switching is required. I have the input side ...
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113
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4N25 Optocoupler design
Below is a simple 4N25 optocoupler circuit that I designed in LTspice.
10 mA is flowing through the input. It works in saturation. According to the datasheet in Figure 2 (CTR-sat), it says 0.7, so the ...
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Calculating current through a diode in a voltage divider circuit
I have a voltage divider circuit which I use to drive two LEDs with different luminous intensity. I understand that this is not the best way to do it but I wanted to control two LEDs with the same ...
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Sending arbitrary bitstream to SFP transceiver: minimum bitrate?
I'm trying to use a Small Form-factor Pluggable (SFP) as the laser source for a homebuilt laser gas analyzer, which means I don't actually care about transmitting data. The plan is to send an ...
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Finding poles of the transimpedance amplifier
I`ve been having problems with finding poles of one transimpedance amplifier.
Acording to LTSpice the first pole should be somewhere around 1.6MHz, but I cant get that (I am getting about 200MHz). I ...
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What could the strange noise in the images be due to? They appear to be composed of 8x8 squares, and many of them contain different patterns [closed]
The question may seem silly, but I am curious about the structure of images from a certain biomedical image dataset.
If you enlarge the following image fragments, you can see that they consist of 8x8 ...
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High-gain transimpedance amplifier with photodiode not functioning as expected
I am designing a trans-impedance amplifier using a TEMD7000X01 photodiode and an AD8551ARZ op-amp. RF is 100 kΩ, CF is 150 pF, and VCC is +3.3 V. The output of the op-amp is connected to an ADC pin of ...
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113
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Is there concept called dual ethernet? [closed]
I came across a word called dual ethernet while working on a project and it got me curious like is the word misspelled or is there any real concept on this?
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How to design a pulsed laser driver circuit?
I want to try a simple theoretical design of a pulsed aaser rriver circuit according to what specified in this guideline from LASER COMPONENTS. Since the guide is not exhaustive, I'd like to get some ...
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Design Suggestions for an Optocoupler Relay Module
I have designed this module to operate with input voltages of 5V and 3.3V (common in most MCUs). Additionally, I have equipped it with an optocoupler to isolate the MCU from the power section of the ...
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350
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Understanding optocoupler's operation through simulation
I am trying to understand how an optocoupler (4N25) works by looking at the datasheet and simulating a test circuit in LTSpice, but I am having some issues.
To begin with, for the sake of trying to ...
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261
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SWD Connection to MCU and Appropriate Configuration for Reset Pin
I aim to establish a connection between SWD header and an STM32 MCU on PCB, having identified the relevant pins on MCU (SWO, SWCLK, and SWDIO). I have two inquiries:
Is it appropriate to connect ...
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336
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Does Optocoupler with Low Collector Current Work?
I am working on a schematic which was not started by myself. From the datasheet of LTV-816S-TA1-D, The CTR is from 300% to 600% and I set the forward current I_f to 5mA.
However I notice that, given ...
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86
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Current measurement from constant current source
I have a constant current circuit using an op amp circuit. I am implementing a current of 21 mA to drive a laser.
Spec of laser: https://www.thorlabs.com/thorproduct.cfm?partnumber=L650P007
I would ...
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122
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Simulating an equivalent circuit model of a laser in LTspice, how does it solve this circuit?
I want to know how LTspice solves this circuit as there are node voltage (vj) dependent current sources (Ist and Isp) present in this circuit. Also, I had an unknown parameter, Ne, whose value I ...
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299
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Zero crossing detector - MCU interrupt is delayed
I'm trying to catch zero crossing (using below circuit) when it exactly happened. Rising and falling edge intervals are not equal and they need 0.3-0.7 ms to reach corresponding logic level. Let say ...
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545
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Connecting 6 push buttons with ESP32 with 1 common pin
Hey all I have 6 buttons that have the following voltage:
I want to hook up a 4N25 to each one of these so I can use the ESP32 as a "virtual push" to each of these buttons. When the button ...
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How does a 4 pin RGB connector work without ground?
The question is in title. Why there is no ground pin on the 12V RGB header? The 5V ARG header which uses only 3 pins has a ground.
How does it work without a ground?
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How to understand output of TSOP4838 IR receiver?
I am testing the output of the following basic IR transmitter/receiver circuits and not getting the result I thought I would.
simulate this circuit – Schematic created using CircuitLab
I have ...
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Is it possible to plot an equation in LTspice? I am supposed to plot an equation like this v(t)=d/dt(ln(pout(t)) + kPout(t)
In the equation mentioned above, Pout is the voltage at some output node in my schematic. Is it possible to plot the above equation? how to plot v versus time?
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Quad IR pickup output inconsistencies
I've designed a quad IR pickup for a stringed instrument. The pickup works well, except that the output level of each string is different. Some strings (particularly the left two channels in the ...
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397
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Characterizing a PIN photodiode's 3 dB bandwidth
I'm currently attempting to characterize a PIN photodiode's 3 dB bandwidth. The photodiode input is a laser source that is being modulated by an ESA RF output that performs a frequency sweep from 0-1....
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148
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Safety regulations (USA) for high-power LED brightness (e.g. 1+ W)
For a "mostly" shielded sequence of 1 W where a user will see light bleed through small gaps in a device and (for argument's sake) might see a direct reflection of one of these 1 W LEDs (a ...
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What is equilibrium carrier concentration in a semiconductor? Is it material specific? How to calculate it?
Is equilibrium carrier concentration dependent on doping density? If it is, then how to know how much the doping density should be for a particular semiconductor device?
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I am simulating an equivalent model of a laser in LTspice shown below. I am supposed to plot the power at node Pout versus the input current
The issue is I am not able to plot the power without adding the load resistor which is not specified in the equivalent circuit.
Is there any other way to plot the power? If not, then what value of ...
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What makes an InGaAs detector more sensitive to infrared light?
What makes an InGaAs detector more sensitive to infrared light than visible light, considering that visible light has a higher photon energy?
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Implementing direct digital synthesis in STM32 microcontroller
I am working on a project that requires phase locking (digitally) of an output signal from a sensor to the reference signal which needs to be done on STM32 microcontroller. I am new to this area, and ...
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Any theoretical reference for empirical equation for estimating oxygen saturation (% SpO2 = 110 - 25*R)? [closed]
The empirical equation used to estimate % SpO2 is based on the observation that the ratio of the red and infrared light absorbed by arterial blood (represented by R in the equation) varies linearly ...
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148
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Difficulties with multiplexing PPG signal in pulse oximeter
I've designed pulse oximeter circuit. When one LED lights continuously, I got perfect PPG (Photoplethysmogram) signal.
Then I measure PPG while blinking LEDS, like that:
I got stuck. There is no ...
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Detection of mechanical relay sticking
I'm exploring new methods to find if relay contacts have been stuck together without using auxiliary contacts of the relay. while searching I find out this block circuit:
at this Toshiba page
as far ...
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Low pass filter (?) in Thorlabs PDs
What is the purpose of this circuit in all Thorlabs PDs? It looks like a second order low pass filter to me, but shouldn't it be two resistors in that case?
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How to drive this specific laser
I've done just a circuit to drive an old laser and it was like this one:
I was wondering if it could be suitable for driving the laser whose datasheet is reported below.
I have these requirements:
...
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112
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Measuring low lux with ambient photodiode
For my application, I need to detect two light levels: pitch black (close to 0 lux) and a low ambient light level of about 0.1 lux (or higher). It seemed like the BH1680FVC ambient light sensor was a ...
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How to choose a phototransistor or photodiode?
I've found a photoresistor (yes, resistor, probably 30 years
old) in my scrap box, attached it to an ATtiny as ambient light
sensor, with a 100kΩ resistor as voltage divider towards +5V.
On power on, ...
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2
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153
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BT136 TRIAC waveform
I am using a TRIAC to switch an AC signal
(a typical example is shown in question Triac Switch Circuit using MOC3021 and BT136).
When a BT136 TRIAC is used to switch a pure sinewave signal, I want to ...
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How can we explain this strange phenomenon with an optocoupler switching?
Two optocouplers are connected according to the circuit below. The input voltage across the first optocoupler is a true square wave (3.3 V amplitude). The first optocoupler is an open collector output ...
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DVD burner laser identification
I just disassembled the DVD writer from a laptop and scavenged some parts. Around where the laser and mirrors and opto stuff are packed together, I extracted these parts.
Which one is the laser diode ...
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521
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What does the VCC pin do in this Optocoupler?
I have this optocoupler, and I am trying to figure out how it works.
What is the VCC pin supposed to do? How does it supply current to the gate pin of the transistor?
https://www.digikey.com/en/...
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Using a LED as a debug serial port
I want to add a debug serial output port to a device that's sealed in epoxy. I plan to use one of three existing 3mm LEDs (red 617nm, green 568nm, or yellow 588nm), ±30° angle, that emerge from the ...
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