The 4N35 is a versatile optocoupler or optoisolator IC that consists of an infrared emitting diode coupled to a phototransistor. It is designed to provide electrical isolation between its input and output, allowing a signal to be transferred between two isolated circuits without a direct electrical connection. This isolation helps protect sensitive electronic components from voltage spikes and surges, as well as reducing electrical noise in signal processing.
This circuit involves an Arduino UNO controlling two 4N35 optocouplers, which are used to isolate different sections of the circuit. The circuit also includes a pushbutton for user input, resistors for current limiting, and a ceramic capacitor for noise filtering.
Open Project in Cirkit Designer
This circuit appears to be a microcontroller-driven array of push-pull solenoids with flyback diodes for protection. The STM32 Nucleo F303RE microcontroller's GPIO pins are connected to the gates of several nMOS transistors, which act as switches to control the current flow to the solenoids. A pushbutton with a pull-up resistor is also interfaced with the microcontroller for user input, and the power supply is connected to the solenoids with ground return paths through the nMOS transistors.
Open Project in Cirkit Designer
This circuit is an emergency alert system that uses a NUCLEO-F072RB microcontroller to send SMS alerts and make calls via a SIM800L GSM module, while obtaining location data from a GPS NEO 6M module. The system is powered by a Li-ion battery and includes a TP4056 module for battery charging and protection, with a rocker switch to control power to the microcontroller.
Open Project in Cirkit Designer
This circuit is a multi-color LED driver powered by a 2 x AA battery pack. It uses NPN transistors to control the illumination of red, green, blue, yellow, and white LEDs, with resistors and capacitors providing current limiting and stabilization.
Open Project in Cirkit Designer| Pin Number | Name | Description |
|---|---|---|
| 1 | Anode (A) | Anode of the infrared LED. Connect to positive voltage. |
| 2 | Cathode (K) | Cathode of the infrared LED. Connect to ground. |
| 3 | NC | No connection. |
| 4 | Emitter (E) | Emitter of the phototransistor. Typically connected to ground. |
| 5 | Collector (C) | Collector of the phototransistor. Connect to the output circuit. |
| 6 | Base (B) | Base of the phototransistor. Optional use for increased sensitivity. |
Input Side (LED):
Output Side (Phototransistor):
Base Connection (Optional):
LED Not Lighting Up:
No Output Signal:
Insufficient Isolation:
Q: Can I drive the 4N35 directly from a microcontroller? A: Yes, you can drive the LED side of the 4N35 directly from a microcontroller pin through a current-limiting resistor.
Q: What is the purpose of the base pin on the 4N35? A: The base pin allows for increased sensitivity and faster switching speeds when used, but it is optional for normal operation.
Q: How do I choose the value of the current-limiting resistor for the LED? A: The value can be calculated using Ohm's law: R = (V_supply - V_forward) / I_forward, where V_supply is the voltage from the microcontroller pin, V_forward is the forward voltage of the LED (typically 1.2V), and I_forward is the desired forward current (usually around 10mA).
Q: Can the 4N35 be used to switch AC loads? A: While the 4N35 itself cannot switch AC loads, it can be used to drive a relay or triac which in turn can control an AC load.
// Example code for interfacing a 4N35 Optocoupler with an Arduino UNO
const int ledPin = 13; // LED connected to digital pin 13
const int optoPin = 2; // Optocoupler input connected to digital pin 2
void setup() {
pinMode(ledPin, OUTPUT); // Set the LED pin as output
pinMode(optoPin, OUTPUT); // Set the optocoupler pin as output
}
void loop() {
digitalWrite(optoPin, HIGH); // Turn on the optocoupler (LED on)
digitalWrite(ledPin, HIGH); // Turn on the LED
delay(1000); // Wait for a second
digitalWrite(optoPin, LOW); // Turn off the optocoupler (LED off)
digitalWrite(ledPin, LOW); // Turn off the LED
delay(1000); // Wait for a second
}
This example demonstrates how to turn on and off the LED inside the 4N35 optocoupler using an Arduino UNO. The same signal is used to turn on an LED connected to pin 13 to provide a visual indication. Remember to include a current-limiting resistor in series with the optocoupler's LED.