Questions tagged [opto-isolator]

An optoelectronic device which combines an optical transmitter and receiver in a single package; commonly used in galvanic-isolated control applications such as power supplies.

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TLP281-4 optoisolator circuit question

I am working with TLP281-4 optoisolator, there is a board which used this IC in it. It connected like this: Why can't I connect 5V to the collector and take the output directly from between emitter ...
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1answer
135 views

MeanWell 3-in-1 dimming

I've got a constant current MeanWell LED driver that has 3-in-1 dimming (100k potentiometer, 0-10V signal or 10V PWM), and would like to control the dimming with a microcontroller. I found a few ...
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95 views

Can you and/or why should you not replace optocouplers with transistors when dealing with slightly different voltage

I stumbled upon this: https://gyazo.com/9f495ed8e9005ab440db8061839f412a so the mdb bus is communicating at a 34v level and the other side is at 5 or 3.3v why are they coupled with a optocouplers ...
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115 views

Voltage sampling from 220vac to 5vdc

I made a 1 phase to 3 phase inverter using arduino and IR2104 to control the speed of an induction motor and it is working perfectly. To complete the protection scheme, I need to monitor voltage of ...
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3k views

Interfacing a button to a microcontroller (and PC) with a 50 m long cable

I am designing a board that will be plugged into a computer and will read the status of a button ~50 m away in an office environment (it's actually a lot closer, but the cable is long). I think ...
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45 views

Using a Optocoupler - Determining Parameters

I'm looking at possibly using an optocoupler to drive a higher powered circuit from a lower powered one. This is the device I am looking at: http://www.vishay.com/docs/83641/il755.pdf The circuit I ...
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55 views

How can I improve this digital-output / digital input (automotive)

I'm creating some circuits required in a student-built electric-vehicle application. There are no heavy loads on the low-voltage +12V system. What I have below is a circuit that does some threshold ...
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34 views

Resistor power dissipation when driving optocoupler from ac mains

I followed this: https://learn.edwinrobotics.com/230v110v-ac-mains-detection-using-arduino-raspberry-pi-and-esp8266-thing/#Step2 With the exception that I used an LTV-814 that doesn't require a ...
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1answer
41 views

Raspberry Pi input protection with optocoupler?

I need to isolate a noisy input to a Raspberry Pi 4. Would this be the most correct way to implement it? I feel like the protection on the input side of the Pi is overkill. Note: Schematic uses a ...
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53 views

24V signal to drive led

I have a PLC which gives 24V DC output. I would like to drive an external LED using 24V. Is this the correct way to drive an led? Which is the right method let me know any changes needed. simulate ...
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2answers
56 views

Tri State/Floating Signal Detection

I'm working on a project for automotive environment in which I need to read signals from the power mirrors switch in a microcontroller. The power mirrors switch controls the mirror's moving directions ...
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1answer
193 views

Automotive Arduino

I was designing a circuit to manipulate in's and out's in a car. I use a step down converter to power up the Arduino. The inputs, in the left of the Arduino are: GIN : General grounded Input. ...
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2k views

Opto-coupled PWM output

I have a circuit with two different ground levels. Using a optocoupler, I want to translate a PWM signal to the new ground level. Does there exist a easier method than the following? (Ideally with ...
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1answer
428 views

Is the ground necessary with an opto-isolated RS422 signal

I have 8 opto-isolated RS422 ports to install. All of them are coming from a single PC card. It provides the opto-isolation for every RS422 port. Every signal is opto-isolated from the PC ground and ...
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602 views

Diminished data rate with logic output optoisolator

I am using a logic output type optoisolator (H11L1S) that has a nominal data rate of 1 MHz, yet in practice I can't even achieve 100 kHz. Where am I going wrong? Is this maximum data rate ...
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29 views

Triac design for switching load to resistive heater

I'm designing a triac-based relay circuit to switch ac mains on-off to a resistive heater. The app note (AN-3004) for the opto isolator I am using, the MOC3061, suggests using a gate resistor value ...
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908 views

optocoupler H22A2 driving a plc input

https://www.vishay.com/docs/83741/83741.pdf example 2 I have existing H22A2 optocouplers that I am trying to run 12vdc through to get a plc input to turn on and off. I am using a 1k resistor on the ...
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25 views

Driving a TC4428 using PC817

I want to drive a mosfet using a mosfet-driver (TC4428). The frequency of turning on-off of mosfet is 5-10 Hz (yes Hz) and duty cycle is 10-20%. I use PC817 as ...
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1answer
55 views

230VAC line voltage sensing using MCU pin

I Am designing a circuit to detect the presence of AC line voltage.It is basically to detect the switch On/OFF for a load. Here is the circuit. Here Input resistor ladder to step down the voltage. ...
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67 views

Replace optoisolator with a resistor

I found this circuit that I wanted to quickly implement. He is using an optoisolator and feeding back the output using it. I understand that the optoisolator is isolating the sensitive circuit from ...
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2answers
63 views

Reverse Polarity Optoisolator

I am looking to detect, if battery is connected to board or not, by adding optoisolator to a battery and connect it to micro controller, before reverse polarity protection circuit. (Which is MOSFET ...
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1answer
548 views

Latching/Non-Latching Relay Driver Circuit with darlington optocoupler

I'm designing a circuit where an ESP8266 controls two types of relays, a single coil latching relay and a normal non-latching relay. The relays are power relays use to control low power electrical ...
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1answer
654 views

High side RC ESC switch

I've been designing a test bench for RC propulsion systems and for that I thought it would be nice to be able to switch the power to the ESC on/off. For this I designed a simple circuit which I ...
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3answers
102 views

Why optocouplers for MIDI Out/Thru?

I found this article: midi-in-through-out Credits by Zynthian I like that it has notification LEDS for MIDI in/out/thru. However, I also notice there are optocouplers for MIDI Out and Thru, while ...
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Optocoupler Failures

I am designing a small PCB that has several digital and relay outputs. The signals to and from the board will be 24VDC, while the logic on the board will be 3.3VDC. There will also be 12VDC for the ...
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59 views

Voltage drop after optocoupler

I don't know what's wrong... I have an ATTiny13 which gives a dummy impulse turning a fan on and off every 2 seconds; so the plan. I attach two power sources (for dummy purpose) before and after the ...
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1answer
667 views

How safety capacitor replaces optocoupler

I see some phone chargers using safety capacitor (after some research I found its safety capacitor)But not optocoupler to isolate in and out . How safety capacitors replace the optocoupler
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46 views

Modification to Arduino 12V Detection Circuit

I'm upgrading the interior lights on an older model vehicle. The plan is to tap into the very simple lighting circuit (always hot with a switch for on-off-door) to detect each scenario. Light switch ...
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5answers
5k views

Can an opto-isolated input be analog?

Title says it all: can an opto-isolated input be analog or are they intrinsically digital? Why: I am looking to purchase a relay control board and am deciding between a few options. Here is my ...
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48 views

What is the expression for collector current (Ic) in function of CTR for optocoupler?

I'm just asking about expression for collector current (Ic) of optocoupler in function of CTR because my simulation results doesn't fit with the CTR=Ic/If equation. Simulating the part CNY17-3 with ...
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85 views

Zero Crossing Signal Timing

I have a zero crossing circuit for dimming lamps exactly like the below According to my calculations: \$ I_{R7} = \frac {V}{R} = \frac {3.3}{10k} = 0.33~mA\$. Considering TCMT1109 transfer ratio ...
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2k views

Isolating PWM From H-Bridge

I have a H-bridge based on FAN7392 drivers. This bridge works at 350VDC to output a approximately 240V 50Hz waveform. This circuit is isolated from rest of the board and I would like to maintain the ...
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1answer
70 views

Optocoupler - Make active low output at active high

I'm currently working on a project and it consists of amplifying a 5V signal from an Arduino to 24V. I made my circuit and hooked it up to a oscilloscope and it shows that the output of the ...
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2answers
78 views

Reading an optocoupler datasheet and calculating the resistors for its input/output

This is a continuation from this question (sort of) I want to replace the relays from an existing circuit with optocouplers and had trouble how to read the optocoupler datasheets as well as ...
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1answer
115 views

Understanding the difference of optocouplers vs relays and choosing the right replacement

I'm a bit overwhelmed by the sheer amount of variations in optocouplers and since I've never used one before in any project I don't really know what criteria to look out for. A colleague of mine ...
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662 views

AC Switching Relay isolation with Optocoupler

I am trying to do a schematic to switch a relay using my MCU. MCU GPIO works at 3.3V. I have come across the following schematic, but unable to calculate proper CTR and thus the value of Base ...
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1answer
59 views

Opening and closing a pair of terminals

I have a device running at 12vdc that has a pair of terminals that can be opened and closed for the device to operate. I understand how to use an optocoupler to open and close the terminals, however ...
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98 views

Optocouplers vs Voltage Dividers

I have a device that has a terminal that goes to 5v at certain times. I wish to sense that voltage with an ESP32. I have built this circuit using an optocoupler: simulate this circuit – ...
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1k views

Audio soft mute using optically isolated MOSFET

I have an audio signal running through a device that switches it over using a mechanical relay, as a result of the DC offsets and the parasitic capacitance on the output (which also connects to a high ...
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3answers
522 views

Normally Closed Optoisolators

I understand that typical optoisolators can logically be considered as "normally open". However I have a situation where I'd like the circuit controlled by the opto to be normally closed, mainly for ...
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23 views

Combined 25V/OPEN and 25V/0V Input circuit

I am designing a board for digital inputs in which I will be receiving 2 types of inputs, 25VDC/OPEN and 25VDC/0V, 10 inputs each. The input signals have different specs but is it OK to design same ...
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2answers
95 views

A question about using optocoupler instead of FET for longer signal wires

After my previous question I had concluded to use the following circuitry to operate this solid state relay: But now I found out that, from the micro-controller(Arduino UNO) digital output pin to the ...
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1answer
93 views

LEDs and high currents

In smartening up my doorbell I've been playing with my illuminated pushbutton and have fallen into a bit of a rabbit hole. The doorbell normally: simulate this circuit – Schematic created using ...
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1answer
109 views

Digital inputs problem [duplicate]

I'm designing a digital I/O module which isolated with optocouplers. I'm done with the outputs, but having a confusion about input side. I will have some switches and sensors to read as inputs, but ...
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104 views

I/O Module with optocouplers

I'm designing an I/O module by using optocouplers for the inputs and outputs which I want to control by a microcontroller. Here are my questions: In the datasheet of optocoupler's output current (...
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94 views

What is the purpose of the optocoupler in this circuit to drive the mosfet/relay?

I'm currently trying to understand a circuit for an ESP8266 relay board. As you can see in the schematics below, an optocoupler is used to drive the relay mosfet. I do not understand, why they are ...
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88 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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1answer
120 views

how does single supply op-amp work while its non-inverting input is connected to ground?

In HCNR200 Datasheet, the page 11, figure 13-A, there is a sample that confused me. In this sample, the Vin is applied to the inverting input and if the electric current passes through PD1, PD1 ...
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5answers
110 views

Relay control by using microcontroller

I'm working on a I/O module to control AC, DC motor and lamps by using relays. But I don't know how to control the relays. Some says I should use optocoupler, some says transistor array. I found an ...
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3answers
64 views

Single GPIO for optocoupled input and output

I want to use a single GPIO pin as optocoupled input and output (at random discretion). Will the following scheme work for any possible combination of input and output? Especially when optocoupler 1 ...