![]() ![]() Initially I did not connect pin 6, the base to anything. When doing research for working with the 4N25 I always saw diagrams of the base not being connected at all, or being connected to ground by a very large resistor in the 100k and above range. Pin 6 (the base of the transistor) is used to tweak the sensitivity of the optocoupler. When the LED in the 4N25 turns on, it causes the input output to go LOW because there is a direct path opened to ground.ģ. The transistor side of the 4N25(pin 4, 5, and 6) reproduces a signal by always being high except for when the LED gets turned on. In all of the configurations of the 4N25 I have always seen output tied in paralell to the transistor sides collector(pin 5). See how the output is the inverse of the input according to the diagram on the right? Test diagram that is shown in the Fairchild datasheet: This is echoed in Paul Hill's Speed Control Examples Using the 4N25 as well as the I'm not sure about other optocouplers, but the 4N25 works on the major principal of sinking current.īefore actually working with the part, I did not understand that you have to configure the optocoupler in such a way that when the signal you are trying to reproduce goes low, the optocoupler should turn ON. I think I got the pins on the optocoupler too hot while soldering them to the breakout board.Ģ. I made a breakout board for this part and after a week found out the that optocoupler was not preforming as it should have. The Fairchild 4N25SM has large enough pin spacing despite being surface mount, that you can easily solder wires directly to the pins for experimentation. This is the way I should have done it in the first place This didnt need a breakout board made for it. Dont waste your time making or purchasing a breakout board for a package size that is large enough to directly solder wires to. The following are a series of descriptions of ideas that I have learned while working with an optocoupler over the last month.ġ. I am writing this after successfully using a Fairchild 4N25 Optocoupler to deliver pulse width modulation from a USB based circuit to the 7.2V circuit in order to control a servo. The idea behind this is that I want to protect the USB based circuit(and my computer) from the large amperages, inductance, higher voltages and other things going on in the RC Car side of the circuit, but still want to be able to control it using a USB device. I want to use an optocoupler for separating a circuit powered by USB (5V) from one powered by a 7.2V RC Car battery. From what I understand, the MIDI protocol requires the use of optocouplers in all devices. Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!ĬircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.An optocouplter or optoisolator is a cool little device that allows you to completely separate sections of an electrical circuit. We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers. Search Questions & Answers Ask a Questionĭid you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.ĬircuitLab's Q&A site is a FREE questions and answers forum forĮlectronics and electrical engineering students, hobbyists, and ![]()
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