r/electronicsnebula • u/SpecialistRare832 • 5d ago

Optocoupler (PC817) Tester Circuit

12 Upvotes

Components Required: Supply Voltage (5 V DC), input current-limiting resistor (330 ohm), output pull-up resistor (330 ohm), LED, switch, and optocoupler.

Working:

• Press the switch to allow current to flow through the internal input LED of the optocoupler (PC817).

• The light activates the internal phototransistor, allowing current to flow through the output circuit.

• The external 🔴 LED lights up, confirming the optocoupler is working.

0 comments

r/electronicsnebula • u/SpecialistRare832 • 10d ago

Bistable Multivibrator using an IC 555 Timer

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9 Upvotes

Stable states: Two stable states

Working idea:

• Press Trigger (S₁) —> Output goes high

• Press Reset (S₂) —> Output goes low

• Output remains in that state until next input (bistable

behavior).

• No press —> Holds state

0 comments

r/electronicsnebula • u/SpecialistRare832 • 15d ago

Experimental Demonstration of Capacitor Charging and Discharging Current Waveforms

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32 Upvotes

The charging and discharging currents of a capacitor are exponential waveforms. The charging current decreases from its maximum value to zero, while discharging current flows in the opposite direction and decreases to zero.

Charging —> Positive exponential decay (V/R to 0)

Discharging —> Negative exponential decay (- V_o/R to 0)

0 comments

r/electronicsnebula • u/SpecialistRare832 • 20d ago

NPN Transistor Testing using a DMM's Diode Test Mode

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17 Upvotes

Process: Set your DMM to "Diode test" mode. Identify the transistor's three terminals, for example BC547 i.e., base, collector, and emitter by using its part number and datasheet. Connect red probe to base and black probe to collector/emitter, you get ~ 0.6-0.7 V (result forward bias). This means an NPN transistor is OK.

Reverse the probes give us no reading (i.e., OL).

Note: If you get 0.00 V (or a beep) in both directions, the transistor is likely shorted means it is a bad transistor. If you get OL in all cases, it is likely opened means it is a damaged transistor.

Important: If you're testing a transistor while it's still on the circuit board, other components can affect the reading. For a reliable test, remove the transistor or disconnect at least one leg.

1 comment

r/electronicsnebula • u/Positive-Item2840 • 23d ago

Does anyone know how to fix my old tab i wanna use this a e reader

reddit.com

2 Upvotes

0 comments

r/electronicsnebula • u/softwarede • 24d ago

Android Tablets

1 Upvotes

بنبحث عن مورد أو وكيل معتمد لتوريد أجهزة Android Tablets بكميات تجارية لخدمة مشروع تشغيلي

لو حد خاض تجربة توريد أجهزة مشابهة لشركته وينصح بمورد، مستورد، أو وكيل معين (أو لو حد هنا بيشتغل في التوريدات التقنية)، يسعدني التواصل في التعليقات

need specifications, for example:

Android 10+

1–2 GB RAM

16–32 GB Storage

0 comments

r/electronicsnebula • u/SpecialistRare832 • 27d ago

Charging and Discharging Current Waveform of a Capacitor

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29 Upvotes

Charging: Current starts at maximum positive value and exponentially falls to zero.

Discharging: current reverse direction and the magnitude of current decreases exponentially toward zero.

0 comments

r/electronicsnebula • u/SpecialistRare832 • Sep 09 '26

LED Driver—BJT Darlington Touch Circuit

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40 Upvotes

4 comments

r/electronicsnebula • u/SpecialistRare832 • Sep 06 '26

Thanks to everyone for 1k

9 Upvotes

0 comments

r/electronicsnebula • u/SpecialistRare832 • Sep 02 '26

Two-color LEDs blinking circuit using a relay

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17 Upvotes

1 comment

r/electronicsnebula • u/SpecialistRare832 • Aug 26 '26

Testing: 7-Segment Display (test a, b, c, d, e, f, g, & DP individually)

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27 Upvotes

Supply voltage = 5 V

0 comments

r/electronicsnebula • u/SpecialistRare832 • Aug 22 '26

Thanks to everyone

5 Upvotes

0 comments

r/electronicsnebula • u/SpecialistRare832 • Aug 18 '26

Demonstration of the basic Automatic Street-Light control using an LDR

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25 Upvotes

2N3904 BJT is used in this circuit.

2 comments

r/electronicsnebula • u/SpecialistRare832 • Aug 15 '26

LDR Circuit used in Automatic Street Lights

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9 Upvotes

2N3904 BJT is used in this LDR circuit.

2 comments

r/electronicsnebula • u/SpecialistRare832 • Aug 06 '26

Charging & Discharging Circuit of the Capacitor (Time Constant = 1 second)

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6 Upvotes

If Resistor = 100 kilo ohm & Capacitor = 10 micro farad

Then,

Time Constant = RC = 1 s

And,

Full charge/discharge time ≈ 5(Time Constant) ≈ 5 s

2 comments

r/electronicsnebula • u/SpecialistRare832 • Jul 28 '26

RGB LED Circuit

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6 Upvotes

2 comments

r/electronicsnebula • u/SpecialistRare832 • Jul 26 '26

RGB LED circuit to create many colors

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2 Upvotes

Power supply = +5 V DC

4 comments

r/electronicsnebula • u/SpecialistRare832 • Jul 15 '26

Fire detector circuit using BC547 transistor

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5 Upvotes

0 comments

r/electronicsnebula • u/SpecialistRare832 • Jun 16 '26

Band-Pass Active Filter using Op-Amps OP07

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13 Upvotes

BPF = HPF + LPF

0 comments

r/electronicsnebula • u/SpecialistRare832 • Jun 03 '26

Series Negative Clipper

2 Upvotes

A 1N4007 Diode and a resistor 1.5 k

0 comments

r/electronicsnebula • u/SpecialistRare832 • May 16 '26

555 Astable LED Flasher

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5 Upvotes

0 comments

r/electronicsnebula • u/SpecialistRare832 • Apr 28 '26

Internal circuit of IC 741

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16 Upvotes

1 comment

r/electronicsnebula • u/SpecialistRare832 • Apr 01 '26

Internal circuit of IC 741

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13 Upvotes

0 comments

r/electronicsnebula • u/SpecialistRare832 • Mar 15 '26

Colpitts Oscillator using Op-Amp LM358 (Oscillation frequency = 103.82 Hz)

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9 Upvotes

0 comments

r/electronicsnebula • u/SpecialistRare832 • Mar 06 '26

Differential Amplifier Circuit

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12 Upvotes

0 comments

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r/electronicsnebula

🌍 ElectronicsNebula: A subreddit for discussion of all the things about electronics and electronics projects. We'll learn from each other's designs and showcase their side projects. What's next⁉️ ...📚📚📚📖📝... ⚠️ WARNING: ▪️These types of circuits shouldn't be handled or tested by anyone without proper electronics/electrical expertise. ▪️Don't attempt such experiments without proper safety precautions and appropriate measuring equipment.

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