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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchTo make the documented PC817 LED flasher, use a 3.7 V battery, a PC817 optocoupler, a 1 kΩ resistor, a 5.6 kΩ resistor, a 220 µF electrolytic capacitor, and an LED. The 5.6 kΩ resistor and capacitor form the timing network; their nominal RC time constant is 1.23 seconds. That is not a measured flash period, so the actual blink rate may differ.
Parts for the 3.7 V circuit
- One PC817 optocoupler, such as the UTSource part used in the Hackster project
- One 1 kΩ resistor
- One 5.6 kΩ resistor
- One LED
- One 220 µF electrolytic capacitor rated for 10 V or 16 V
- One 3.7 V battery
The component list and build description come from the Hackster PC817 LED flasher project. Follow its circuit diagram for the complete wiring: the text instructions alone do not fully establish the LED and battery connections or replace checking the package pin orientation.
How to wire it
The PC817 has four pins: pins 1 and 2 connect to its infrared LED input, while pins 3 and 4 connect to its phototransistor output. Confirm the pin numbers against the package and the PC817C datasheet before soldering; do not infer pin orientation from the component’s appearance alone.
- Place the 1 kΩ resistor between PC817 pins 2 and 3, as specified by the project.
- Connect the 5.6 kΩ resistor to the optocoupler at the resistor-capacitor timing junction shown in the project diagram.
- Connect the 220 µF capacitor to pin 3, observing its polarity. Electrolytic capacitors are polarized.
- Wire the LED and 3.7 V battery to the resistor and optocoupler arrangement shown in the diagram, checking polarity and connections before applying power.
The Hackster build describes the battery positive as connected to the LED and 5.6 kΩ resistor. Because its prose does not specify every node as unambiguously as a schematic, use the linked diagram rather than treating the assembly steps as a complete netlist.
#1 Best Overall
- Photocoupler output type: phototransistor.
- Number of pins: 4.
- Needle distance: 2.54mm.
- Package Quantity: 50 pcs.
- Application: PC817 optocoupler is widely used in computer terminals, thyristor system equipment, measuring instruments, copiers, automatic ticketing, household appliances.
Why the LED flashes
The project describes a repeating charge-and-discharge cycle: the capacitor charges through the timing path and drives the PC817 input; once charging current falls, the input returns toward ground and the capacitor discharges; charging then begins again. The changing optocoupler state makes the LED flash while power is applied.
The PC817 separates an infrared LED input from a phototransistor output. In this build it is part of the flasher circuit, but do not assume the assembly provides a safe isolation barrier in a finished product: layout, wiring, component ratings and the surrounding circuit also matter.
Rank #2
- ALLECIN PC817 is a Single-channel dual inline package photocoupler- Perfectly suitable for variety electronic experiments.
- Number of Pin: 4; Pin Pitch: 2.54mm.
- Features: High isolation voltage between input and output & Double transfer mold package.
- Widely Application: computer terminals & SCR system equipment & measuring instruments & photocopiers & automatic ticketing & household appliances.
- Humanized packaging for easy storage and use. ### Please confirm the data before purchasing.
How to change the flash rate
The timing network follows the RC relationship: increasing resistance or capacitance generally lengthens the charge/discharge interval, while reducing either generally shortens it. For the listed 5.6 kΩ resistor and 220 µF capacitor, multiplying the nominal values gives an RC time constant of about 1.23 seconds; the project rounds this to 1.2 seconds.
An RC time constant is not the same as a measured blink period. The project does not report instrumented flash-rate testing or component-tolerance measurements, so use the calculation as a starting estimate, not a promise of a particular number of flashes per minute. Change one timing component at a time and measure the resulting cycle if the rate matters.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteRank #3
- 1-Channel PC817 optocoupler isolation module adopts 5.0 pitch screw terminals for convenient wiring.
- 1-way 817 optocoupler drive terminal input signal voltage: DC 3V-5V/12V/24V (optional); Output signal voltage: wide voltage suitable for DC1.8V-24V.
- The 1-way optocoupler isolation module is suitable for isolation when the output level of the single-chip microcomputer is used to drive inductive components such as motors, and anti-interference protects some circuits of the single-chip microcomputer.
- PC817 1 channel way optocoupler isolation board are good as the level converter(NPN-PNP, PNP-NPN), and can also be used to input a signal to MCU in isolation or MCU control another device in isolation.
- Photoelectric isolator rail holder PLC drive motor board output level of the single-chip microcomputer is low, and the driving voltage of the driven module is high for level matching.
Ratings and practical cautions
The PC817C datasheet lists absolute maximum ratings of 50 mA input forward current, 50 mA collector current, 35 V collector-emitter voltage, 5000 Vrms isolation and an operating temperature range of −30 to +100 °C. These are maximum limits, not recommended continuous operating targets. Size the resistors for the actual supply and expected current, and keep the optocoupler within its datasheet ratings.
Use the capacitor’s marked polarity and a voltage rating above the supply voltage. A 10 V or 16 V capacitor is specified for this 3.7 V example. Before powering the circuit, check the PC817 pinout, capacitor polarity, LED polarity, solder joints and supply connections.
Rank #4
- Photocoupler output type: phototransistor
- Number of pins: 4
- Needle distance: 2.54mm
- Package quantity: 50 pieces, packed in a durable and resealable plastic storage box.
- Application: PC817 photocoupler is widely used in computer terminals, SCR system equipment, measuring instruments, photocopiers, automatic ticketing, household appliances
When to choose another flasher
This PC817 circuit is a compact, low-part-count option for a simple indicator where a rough, adjustable blink is sufficient. It is not a documented choice for precise timing or substantial LED drive. A 555 timer or microcontroller is generally a better direction when timing accuracy, greater drive capability or programmable patterns matter. The cited material contains no controlled head-to-head test, so those are design trade-offs rather than measured superiority claims.
Related 12 V examples should not be wired as though they were the 3.7 V circuit. A 2025 car-alarm blinking-light article lists a 470–1000 µF capacitor, 1 kΩ input resistor and 10 kΩ pull-up; a June 2026 video listing describes a PC817 circuit with 1 kΩ, 10 kΩ, 100 µF/25 V and a 12 V LED. Those are different variants with different supplies and component values.
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Best Value
- PC817 Optocoupler Isolation Board 2/4/8 Channel 817 Voltage Isolation Module
- Each channel of PC817 Optocoupler Isolation Board is independent, can control different voltage at then same time
- The jumper cap can be used to determine whether the output terminal is high potential output or low output.
- Pack of 2 pieces, it means you will get them two SAME units in one type, not two mixed types.
The original project suggests night-indicator use and claims operation for months from a single 3.7 V lithium battery, but it reports no measured battery-life, brightness or long-term reliability results. Treat that duration as an unverified project claim, not a performance guarantee.
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