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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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14 views

Triac gate and T1 short circuit forever with inductive load

I am using MOC3042 with BT139 and snubber 390ohm/2W and 10nF/400V to on/off motor from microcontroller, I can't find data about the motor as it's an old one but it drives quite large shutter
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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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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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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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1answer
136 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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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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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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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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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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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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103 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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98 views

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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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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1answer
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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79 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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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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60 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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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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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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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
71 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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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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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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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 ...
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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
144 views

Why does this Mosfet get Hot?

I have an IRF740 mosfet that doesn't get hot in one circuit but then gets completely hot in another identical circuit and for the life of me can not figure out why. Well the circuits aren't exactly ...
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53 views

What could be the reason SPICE is outputting very different CTR curve for this optocoupler?

For a 4N25/26 I tried to plot the CTR vs LED Current graph by simulating the following circuit. To obtain results similar to the one in the datasheet I keep Vce constant at 10V and sweep the forward ...
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84 views

Does Hall flow sensor require an optocoupler when using STM32 MCU?

I'm using an STM32F103 to measure water flow through a pipe using Hall flow sensors. My power supply is 12V DC to 5V/3.3V DC. STM works with 3.3V and Hall sensors with 5V levels. I've configured the ...
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42 views

Optocouplers common resistor

I have seen optocoupler series with common cathode and resistor on every anode. My question is whether or not one resistor on the cathode side will be sufficient, with the right wattage, of course, ...
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59 views

Can we extract CTR parameter of an optocoupler from its SPICE model this way?

Regarding 4N26 optocoupler, I tried to obtain the following results from the datasheet by LTspice: So as in the test condition I set the forward current 10mA and I set the Rload such that Vce = 10V. ...
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42 views

How to estimate the overall CTR of this optocoupler from its test conditions

As a part of a system I need to replace a proper opto-coupler with an old one which had insufficient CTR for the given circuit section without changing any other component: The pulse input is 0..5V ...
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49 views

Suggestions on wiring PCA9685 i2c + TB67H303 motor ic

I'm trying to design a circuit in order to use the TB67H303 motor driver with the ATMEGA328p and the i2c protocol by using the PCA9685 controller. I never used the TB67H303 and the PCA9685 chips ...
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72 views

Resistance issue in a triac-optocoupler switch

I have made the following circuit to control my water pump with Arduino(UNO R3). I have tried many resistors (calculated myself) to limit current in the optocoupler and triac, but failed to carry the ...
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49 views

Opto-coupler (CTR) and PWM/Relays

I'm VERY confused about saturation and calculating it. As i increase the resistance of photo diode of opto-coupler (4N35) the resistance between collector and emitter increases too. How the ...
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106 views

Opto-coupler circuit - selection of resitor [duplicate]

I have a circuit like below. I wanted to know how these resistance values were calculated. I wanted to use 12V/24V in place of 9V. Let me know selection of opto-coupler and resistance value.
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31 views

optocoupler components design

I'm new on this forum, I'h planning to deploy a lights home automation and need some help about how to calculate the resistors and capacitors associated to a PcF817 optocoupler in order to get 5V at ...
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1answer
74 views

Open Collector to drive PNP without Pull-Up

I need to generate a current signal between 12V and GND, which has to have galvanic isolation. For this, I want to use an optocoupler. Maximum permittable rise / fall time: < 1µs Output side Vcc: ...
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1answer
52 views

Reading a low voltage signal from a battery connected to a transformer

So currently I am trying to read the current draw from a battery that is being run through a transformer to generate an arc to light a gas burner. I have a roughly 1 ohm piece of wire that I am ...
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37 views

Triac Driver Datasheet - LED Trigger Current

Looking at the datasheet for MOC30xx (here: http://www.farnell.com/datasheets/1806097.pdf) I see the following note on p4 under the table outlining the respective LED Trigger Currents of the various ...
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2answers
79 views

Purpose for Shunt Resistor on Opto Isolator Input?

I was looking at a BeagleBone Black Cape and became curious on an input circuit to the BeagleBone GPIO (used for a NPN proximity sensor). Upon further reverse designing, I notice a // 220Ω shunt ...