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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Ćuk converter implementation

I am trying to design a 50 W non-isolated Ćuk converter. I am using the IRF540N MOSFET which is driven by a 555 timer-TLP250 setup, using the fast-recovery BY399P diode. I am trying to find a design ...
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Optocoupler as UART communication

I am using the LTV-816S optocoupler for isolated data communication. When I give 4V supply to U1.1 then I get 3.3 at RX. but when I give a signal (4V) at U1.2 pin then at Rx I should get 0 but I am ...
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Optocoupler selection for detecting 24 VAC input with ESP32

I'm looking to detect HVAC thermostat calls using ESP32 GPIO inputs. I have a total of six inputs (two compressor speeds, blower, reversing valve, and two aux heat levels). Nominally 24 VAC, but my ...
2 votes
4 answers
142 views

How does Whitebox labs get isolated sensor boards when they are using a single power supply?

Whitebox labs makes "Electrically Isolated EZO™ Carrier Boards" which are isolated boards for Atlas Scientific sensors such as pH. I don't understand how can you get an isolated board if ...
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Drive long cable directly with opto isolator 6N137 (open drain OP)

I would like to use serial comms between atmega328p microcontrollers over lines up to about 20 meters long, at speeds of around 9600, with the first choice of cable being cat5. Opto isolating them ...
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Microcontroller digital input isolation using optocoupler

In my project I'm using an STM32F401 controller. I want to provide a digital input to one of its GPIO (3.3V maximum) pins to read an industrial sensor output. I'm advised to provide isolation between ...
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Reading neutral gear from F150 transmission range sensor

We're converting an F150 to hybrid, and I'm working on having our system be able to tell when the truck is in PRND. Primarily, I'd like to know when it's in neutral - the others should come as a ...
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How to drive a 15 Vdc relay coil from ESP8266 3.3 V logic

I want to control a series of Zettler AZ2100–1A–15DE relays with an ESP8266 Wemos D1 Mini microcontroller. I thought I could do this with an optocoupler, so I bought an 8-channel PC817 board from ...
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Will this 24 V relay driver work?

I am not sure about the 24 V which drives the transistor base. Is this circuit correct? Do I need some modifications? The current rating for D2 is 200 mA. Is that high enough?
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M-Bus optocoupler application

I'm designing an M-bus circuit and when I look at the datasheet, it says I need to use a UART. You can see the connection by looking at the first schematic: When I looked at the same circuit with the ...
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Choose appropriate opto-isolator for 230 Vac zero-cross detection circuit

I struggle to understand the datasheet for opto-isolators. I am making a 230 Vac circuit with a full-bridge rectifier. What should I look for when choosing an appropriate opto-isolator? I've been ...
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ESP32 opto-isolated relay board not working - PC817 opto-isolator, 2N3904 NPN BJT and SRD-05VDC-SL-C relay

I have just finished soldering my "custom designed" ESP32 PCB board that I'd like to use for management of 6 x 24 Vac irrigation valves. Given my limited electronics knowledge, for ...
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Designing a galvanically isolated analog transmission circuit with IL300 and different power supplies on both sides

I'm having trouble understanding how this circuit (suggested in the datasheet of the IL300) would behave with a different power supply on both sides of the opto-coupling. The datasheet assumes that ...
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Connect 3 mm jack with 4N25 optocoupler to 8 Ω speaker

I want to take an audio signal from a smartphone's 3 mm jack plug, pass it on to a 4N25 optocoupler,, and get the sound from an 8 Ω speaker. I don't know how to connect them to each other. Can you ...
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TLP3556A MOS switch doesn't seem to turn on

We are using this photo MOS relay in one of our designs. This design is in production and we test every relay in QC. Recently I came across a failed unit with one relay not turning on. I checked the ...
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Differential receiver: 75176 vs optocoupler

I have an incoming differential signal for my PCB to be designed which I have to read. I also need to isolate the incoming differential signals from my PCB's digital system, so I will be using a dual-...
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Sensing a USB charger state via an Arduino powered via a separate USB charger

I want to sense the state of a 240 outlet. I have an adapter plug that I believe will allow me to use a standard USB charger (rated 120/240 V) to provide 5 V when the outlet is powered. I also plan on ...
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Is this a reasonable way to determine if an optocoupler transistor is operating in the saturated region?

I found myself thinking about some 50, old (20+ years) optocouplers that I have (removed from working equipment, purchased somewhere or other, or I don’t remember where they came from), and began to ...
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Using an optocoupler to separate a 4-20 mA loop

I have a PLC that is powered with 3.3 V and a sensor powered with 12 V that outputs a 4-20 mA signal. In order to allow the signal to be readable by my PLC while isolating the current in the 12 V loop ...
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2 votes
2 answers
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Switching PNP transistor by using an opto-isolator

I have a problem with a circuit as shown below. I want to drive a pump with the Pump_enable signal but no metter how is this signal state - high or low, the Q3 and Q2 tranistors are always on and ...
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Why does optocoupler 6N137 have a negative enable current?

I don't understand how can I enable/disable the 6N137 optocoupler, because in the datasheet a negative current is shown. Is that a mistake in the sheet? It states that the low/high voltages are ...
6 votes
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784 views

Mains frequency meter using an optocoupler

I built a frequency counter using an ESP32 to measure frequency in Hz. To measure mains frequency, I used a PC817 optocoupler. First I drove the LED of the optocoupler using 3.3 V PWM signal and ...
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Using AC solenoids with rectified DC [closed]

If one wanted to avoid triac opto-couplers for AC solenoids, would it be OK to rectify the AC, without filter capacitance or regulation, then drive from a transistor opto-coupler? I would think the ...
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Isolated bidirectional data input/output

I am trying to work out how I could set up isolated bidirectional data input/output. So far this is my schematic but I still feel like its not going to work. is output MOSFET Q52/Q53 going to hold ...
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How can I control an input of a Siemens PLC with a 4N25 optocoupler?

I need to turn on/off an input of a Siemens PLC controlled by an external output of another machine. I used an optocoupler because I need to isolate both circuits. I have not been able to make this ...
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Optocoupler + MOSFET PWM amplifier timing issue

I want to drive a 12V, 1.5A valve from a microprocessor and also provide some isolation. The MCU outputs 3.3V logic, and I have this output going into a common source amp & also have a resistor in ...
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Isolated serial circuit - Works only 1 way

I have the following circuit for an isolated serial port. 6N137 is a high speed opto, so baud rate is not an issue. The problem with this is that it works only 1 way i.e. CNB -> CNA transmission ...
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Optocoupler Ltspice model

How are the Ltspice library optocouplers modeled? E.g. PC817 has this one: ...
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How to design around an opto-isolator

I want to control another circuit that is completely isolated from the ESP32. I decided to use an optoisolator. Both the ESP32 and the second control board are powered by 3.3V but they are independent ...
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What is the purpose of this transistor pair on the front of the optocoupler?

I'm trying to understand the function of the transistors on the input to this optocoupler. Is this a standard/common transistor configuration (that has a name)? I'm having trouble finding a match in ...
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Does placing two optocoupler one below another in PCB design affect any signal?

I am working on a circuit where I am using multiple ultrasonic sensors which work on 24V, to read the sensor output through a microcontroller that accepts 5V. I am using optocoupler PC817 to maintain ...
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Multiple NPN driving single PNP

In my circuit I have multiple NPN collectors tied together driving a single PNP which turns on a ATTINY10 anytime the Optocouplers turn on. The logic I want is: Optocoupler turns on, indicator LED ...
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Optoisolated PWM control of resistive and inductive load using Arduino

I want to design a circuit capable of controlling the voltage of either a inductive (electrovalve) or resistive (heating cord) load. I want to have a variable voltage for these loads: for the ...
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MCU not turning on via high side PMOS or PNP BJT

This board basically senses 24 VAC and drives a relay using the attiny10 as delay timer (already tried 555). The board will only be driving a few LEDs < 12 mA and a 5 V relay with ~40 mA coil ...
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Transmit changing shunt resistor voltage value using analog optocoupler

I would like to use the IL300 to transmit the voltage of a shunt-resistor. The voltage value of the shunt changes between 0 up to 1 volt in 1ms depending on the load. On the receiving side of the ...
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How many optocoupler outputs can I stack in series?

I have 44 devices - each which provides a 5V output when active and operating correctly and 0V when not. On my microprocessor, I need to check if all 44 are active or not (don't need to know if ...
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Flyback: opto/Zener feedback circuit

Could someone explain the difference between these two flyback feedback circuits, and how the second circuit works? Any application note available would be a favor for me.
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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 to find a fast optocoupler (or how to read the datasheet)

I am looking for an optocoupler that can sustain a 400kHz signal. Now the question is how can I find out from a datasheet whether it does? Looking at a typical PC817 datasheet I see the following ...
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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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Do I need a current limiting resistor with an industrial rail DIN optocoupler?

I'm going to use this industrial opto-coupler: Optocoupleur RS PRO, montage Rail DIN, 6 mA In its specs document they don't mention the need of a current limiting resistor. I always add a current ...
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NPN transistor on optocoupler ground catching on fire

I was experimenting with ways to cut power to my board and so I added an NPN transistor on the low side of an optocoupler (Q202.) I noticed my voltage regulator was oscillating from 3.3V to GND every ...
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Linear Analog Optocoupler Arrangements

For optocouplers with a second photodiode for feedback for linearization, what is the functional difference between the two positive input stage configurations below? simulate this circuit – ...
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How to isolate (and transmit) a 0-5V DC analog signal using an optocoupler circuit

I am trying to isolate control signals that are used to remotely operate a variable frequency drive. One is a 0-5V analog voltage signal that give the VFD its set point. I understand that optocouplers ...
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Optocoupler or DC/DC-converter for generation of trigger voltage

In my project I would like to trigger an external device with my electronic trigger system. The trigger voltage of the trigger system is 5 V, while the external device needs 24 V to be triggered. In ...
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Low Side Parallel MOSFET Drive [closed]

I'm doing a 12V to 230V push pull inverter design & need to drive it via two MOSFETs for each transformer tapping. Mosfets feeds by an optocoupler PC817. The frequency is 50Hz coming from a PIC ...
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Optocoupler necessary when grounds already common?

I have a 24V solenoid device, that is able to push and pull a small pin, that I would like to control with a 5V micro controller. The solenoid has a reed switch connected to 24V that indicates whether ...
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Problem with optocoupler + MOSFET circuit switch

I am trying to design a simple LED switch controlled by a GPIO on an STM32. I have designed the following circuit but it doesn't work as expected: GPIO and MCU_GND are from the microcontroller. From ...
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Would this isolated AC peak voltage detection circuit work?

I have adapted the circuit from Michael's circuit in Efficient method for isolated detection of AC voltage without a stepdown transformer to detect on either side of the positive half-cycle peaks, ...
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131 views

Why TRIAC is not triggering?

I'm trying to trigger a TRIAC BTA16-800 using an MCO3021 optocoupler. I have a two-channel power supply, in one of them I'm pulsing the optocoupler at 120 Hz and the other channel is configured as a ...

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