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.

Filter by
Sorted by
Tagged with
38
votes
8answers
19k views

Why are relays so frequently driven by optocouplers?

Since the advent of the many microcontroller development boards, like Arduino, there have been a number of relay modules sold to drive mains AC loads. A lot of these seem to use an optocoupler, ...
24
votes
4answers
11k views

Optocoupler with phototransistor base lead

I'm thinking about using 4N25 optocoupler - it has a separate lead for base of phototransistor. How do I use it? I suppose I can't leave it floating?
24
votes
2answers
33k views

Criteria behind selecting pwm frequency for speed control of a dc motor?

I'm working on a speed control circuit for a brushed dc motor (24v, 500rpm, 2A, 4kgcm). The main components that I plan to use are PIC16f873, 4n25 optocoupler, IRFZ44N MOSFET, BY 500 - 800 diode(for ...
23
votes
3answers
70k views

How to drive a MOSFET with an optocoupler?

What's the proper schematic for driving this MOSFET from a microcontroller pin through this or this optocoupler? The MOSFET will drive a motor @ 24V, 6A.
20
votes
4answers
19k views

How do I select the accompanying components for an optocoupler?

I'm using an optocoupler (MOC3021) to sense the On/Off state of an electrial appliance using a microcontroller ATmega16L. How do i go about doing this? My mains supply specs are 230V, 50Hz. How do I ...
14
votes
2answers
964 views

Why does this optocoupler's datasheet recommend splitting a current limiting resistor in two?

And not only that, they also want to keep a ratio of R1/R2=1.5 The opto in question is ACPL-M21L by Broadcom Here's a link to the datasheet: https://docs.broadcom.com/docs/AV02-3462EN Thanks.
13
votes
2answers
19k views

opto isolated arduino input

I want to protect a pin with an opto isolator to get an external signal from an electrical meter (35VDC max, 50mA max, 240ms pulse width). The purpose is to count the pulses. Do you have some ...
12
votes
4answers
8k views

Optoisolate 2MHz SPI communication

I need to isolate the SPI communication between two chips. The bottleneck of the communication is on the slave, which apparently can handle up to 2MHz SPI clock ...
12
votes
2answers
14k views

Optocoupler input protection

I have to provide some isolated inputs that accept 12-24V. There should be some protection against reverse polarization, transient over-voltage and permanent over voltage (up to 40V) to some degree. ...
11
votes
4answers
36k views

Digital Dimmer With Microcontroller

I want to build a digital dimmer for resistive Loads. I have found this circuit for that: The input voltage is 220VAC 50Hz. The red box in the picture is for ...
11
votes
3answers
15k views

Difference between Zero-Crossing Optoisolator and Regular Optoisolator

I am trying to find any documentation on what the purpose is of a Zero-Crossing Circuit TRIAC Optoisolator. The datasheets don't explain the concept well enough. If you do answer, please include ...
11
votes
6answers
3k views

Using an Opto-Isolator to change an Op-Amp's Amplification

Consider this circuit, which is a standard non-inverting amplifier with an amplification of A = 1+R1/R2. I now want to be able to change this amplification value ...
11
votes
4answers
3k views

Validate Triac circuit

I'm designing a device to switch a heating device driven by mains power. I've done quite a lot of research and realize there's a lot of information out there but as i'm dealing with potentially deadly ...
11
votes
2answers
5k views

Why Snub an Optoisolator?

I am using an optocoupler and a power triac to switch 120VAC supply to an ~108 watt fan. The datasheet for my optocoupler requires me to snub the optocoupler output when I'm switching an inductive ...
10
votes
4answers
17k views

TRIAC dimmer, circuit design help (resistive load)

Okay guys, I've been tasked with making a light-dimming control system for a 240V heat lamp dissipating around 250W. I need to adjust the heat output on the lamp by control from a microprocessor. I'm ...
9
votes
1answer
3k views

What are the differences between optoisolator output styles?

Digikey lists optoisolators with several output types: Darlington Darlington with base Photo FET Photovoltaic Photovoltaic, linearized Transistor Transistor, with base What are the differences among ...
9
votes
1answer
5k views

MIDI IN : many circuits

I'm building a MIDI IN to serial port RX cicruit (for Raspberry Pi, or Arduino, or anything else...) using a 6N138 optoisolator. But I find many different circuits, I don't know why there are so ...
9
votes
1answer
18k views

Optotriac+triac: how do I calculate the gate resistor

I am building a small circuit to turn on/off a 200W heater. I am using a MOC3023 and a BT136. At the datasheet of the the optotriac, this circuit is recommended: My question is how is the 180Ohm ...
8
votes
4answers
2k views

Buffering a Digital Microcontroller Signal for Connecting to an Optocoupler

I frequently work on projects in which I use optocouplers for isolating digital +5VDC control signals (for example, from a microcontroller) from the rest of the circuit. However, since these work by ...
8
votes
4answers
2k views

Detect 220 VAC with a Raspberry Pi

I want to build a simple device to check if the light is on or off. I found some schematics but I need to be sure that it is safe. Source : How to detect 220 VAC voltage using an opto-isolator My ...
8
votes
4answers
2k views

Why are optoisolators white?

I've noticed that most of the opto-isolators (optocouplers, opto-triacs) have a white package. Why is that?
8
votes
1answer
11k views

How do I choose my optocoupler to drive a solenoid with a MOSFET?

I need to drive a solenoid with a MOSFET. The solenoid is an 8W solenoid and it will be connected to a +12V voltage. And this drive command have to be isolated with an optocoupler but I don't know ...
8
votes
1answer
4k views

How is this 5-24V input circuit working?

Since I require some kind of wide range input (going to a microcontroller) for a new project, I looked through some designs that are already in use (or were considered at some point) for other ...
8
votes
3answers
6k views

Shift Register output to Relays

sorry for the length. This is a continuation of my recent question. I have an optocoupled 8-relay board that I’m trying to connect to my microcontroller. I have placed a 74HC595 shift register inline ...
8
votes
4answers
17k views

When should I fire the TRIAC's gate when controlling an inductive load (AC motor)?

I'm using a combination of opto-triac + TRIAC to control a 230V AC motor with a microcontroller. For detecting the zero-crossing of the voltage I'm using another optocoupler. I know that the AC motor ...
8
votes
3answers
10k views

Difference between optoisolator(optocoupler) and solid state relay?

I have been looking into relays and optoisolators. I am aware that there are different optoisolators, with some having a transistor on the detector side which allows current to flow in one direction ...
7
votes
2answers
14k views

driving a relay with transistor and Opto-isolator

I am very new in electronics. I am controlling a relay with stm32 micro controller. For the isolation I have used a 4N33 opto-isolator. As my relay coil needs around 250 mA, I used a mps222 ...
7
votes
3answers
4k views

Opto-coupled RS-232 receive circuit

I am looking into a implementing a low-cost RS-232/422 opto-coupled receive circuit. The aim is surge protection and tolerance to DC offsets. The challenge is that the inputs should be completely ...
7
votes
3answers
642 views

unclean signal at the output of an optocoupler

I use a FOD260L optocoupler and here is its datasheet and diagram below pin 2 is connected to an atmega168a (supplied by 3.3V ) via 270 ohm resistor. pin 3 is connected to ground of the MCU. On the ...
7
votes
3answers
4k views

Can LEDs or optocouplers be used without a resistor if PWM is used?

LEDs are often connected through a resistor and the purpose of this seems to be to lower the voltage across the LED to around 1.8V. Can PWM be used to lower the voltage instead of a resistor? If so, ...
7
votes
2answers
6k views

Arduino Uno with 12V pump: transistor or optocoupler+12V relay?

I'm not a real expert in electronics but I'm going to start a new project that has completely captured me. I need to drive a 12V pump with my Arduino Uno. The pump is "Dp0102" (12V, 0.7A). To power ...
7
votes
1answer
1k views

Using the VO2223A to switch a 230Vac LED lamp

I'm looking for something that can switch on and off a 230 Vac, 26mA LED lamp, under microcontroller control. Would a VO2223A, driven by (say) a PIC or Arduino, work as a low-current SSR? The load ...
7
votes
2answers
2k views

Optocoupler high side vs low side switch

I have a NPN Darlington Optocoupler that I have been using for low side switching. I was wondering if it would be okay to also use as a high side switch? Optocoupler Datasheet simulate this circuit &...
6
votes
3answers
1k views

No current through AC optocoupler

I am just testing this component MOC3021 optoisolator, its datasheet can be found here. This is my circuit in Proteus: Please forgive me for my ignorance of electronics, I have my background in ...
6
votes
2answers
5k views

Under what conditions does an optocoupler work fastest?

I want to use the optocoupler FODM452R2 in my design. I want this optocoupler to run as fast as it can (i.e.; work with minimum propagation delay and least rise/fall times). What is the optimum R1, R2 ...
6
votes
4answers
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 ...
6
votes
3answers
4k views

Isolating motor control signals from microcontroller from high voltage/current lines

We need to design an integrated DC motor controller/driver, which will be under microprocessor control. Due to space requirements, either the digital and analog circuitry will be on a single PCB (...
6
votes
4answers
2k views

Analog isolation vs Digital Isolation

I am designing an ADC front-end circuit that will accept a 230 Vrms mains connection. My goal is to measure the RMS voltage of the mains. Though not really necessary, I think it would make sense to ...
6
votes
4answers
2k views

4N35 opto-isolator for MIDI input does not work?

I have the following circuit which I would like to use to connect a MIDI enabled device. I am not getting any signal on pin 5, could it be because the resistor from the base to ground in too small? I ...
6
votes
2answers
2k views

Opto-isolator output from collector vs. emitter

I have an Isocom ISQ2X quad opto-isolator (datasheet) that I will use to drive a logic input. The opto-isolator's simplified model given by the datasheet is pictured below. The transistor base pin is ...
6
votes
1answer
1k views

Zero Cross Detection Circuit for line voltage [duplicate]

Possible Duplicate: How can I detect a power outage with a microcontroller? I'm doing some research with the goal of eventually creating a light dimmer controllable from a micro controller. I've ...
6
votes
2answers
2k views

How to eliminate Bluetooth noise in electric guitar

After learning more about this problem, I have continued this question here. I am trying to remove noise from an electric-guitar circuit that I have created called the ArduGuitar. My circuit ...
5
votes
3answers
2k views

Why does this optoisolator circuit behave like that?

I use 4n25 optoisolator IC. When the duty cycle of Arduino is close to 100%, I expect the voltage across R2 to be 18 V. This happens when R2 is 47 kΩ. I work in a group and my team found that ...
5
votes
2answers
4k views

What is the correct way to measure voltage with an optocoupler?

I'm using an optocoupler to measure a voltage, I'm making a current loop to control the current through the LED, so I'm using three op-amps: one to measure the voltage, one to set up a current offset ...
5
votes
6answers
1k views

Optoisolate two ICs sharing same power supply

I have two ICs. The former acts like an ADC, measuring the voltage in a power outlet and transmitting the result to the last. Both ICs requires 5 Volts to work. I ...
5
votes
4answers
11k views

120VAC 60Hz Zero Cross Detector

I'm designing a digital phase-controlled light dimmer, and I need a zero-crossing detector circuit. From what I've read, it's a bad idea to wire the AC main directly to the microcontroller through a ...
5
votes
2answers
3k views

Is a protection diode needed on a TRIAC optocoupler and what for?

Please refer to page nine of the Sharp S108T01 / S108T02 datasheet: Is this diode needed - why/why not? How do I choose the correct diode, if yes? UPDATE: Thank you all for your educational inputs....
5
votes
2answers
2k views

Why is this optocoupling circuit useless?

Could someone explain me why I can't use the same ground when optocoupling? How can the uC get damaged if there is a short circuit in the phototransistor side?
5
votes
3answers
4k views

Measuring voltage/current digitally on two separate power supply rails

I'm designing a dual-rail DC power supply, with the two rails completely separate (except for sharing a dual-secondary transformer). The main design should work as-is, only by adding a fuse + mains ...
5
votes
1answer
1k views

Why is there a minimum Ic for a optocoupler?

I got confused when I saw this on a HCPL-181 optocoupler datasheet. You can get the datasheet here: HCPL-181 datasheet. So what would happen if the collector current goes below 2.5mA? (In fact I ...