#1849 Linear Optocoupler (part 1 of 3)

Comments · 106

• JX

  @JxH · 2 years ago

  A wise man once advised, "Never use a 1k resistor; people will assume that you just guessed."

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• RI

  @rickeymh · 8 months ago

  Wow!  This is provoking a lot of memories for me.  I was working for a now defunct company called 'circuit processing apparatuses' back in 1980.   We were trying to use a HP photo-Interrupter to detect movement of a product in a vacuum.  To ensure no false triggering, we gated the signal at a couple hundred KHz.  However, we quickly realized that the bandwidths of these HP devices were not up to the challenge.  My lead Engineer, pointed out this same system that you were explaining.  Through a lot of trial and error we were able to get this circuit to work.  Great memories.

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• JX

  @JxH · 2 years ago

  Been there, done that. <br>Used a bulkhead (bolt-shaped) optocoupler to couple audio into a system where we had to ensure that absolutely nothing went the other way.<br>The LED and Phototransistor were given the old Y=mX+b treatment to linearize and center them within the available dynamic range.<br>We didn&apos;t even spend much time analyzing it, but very simply employed trimmer pots, with very generous range, to set the bias (offset) and gain on both sides of the bulkhead.<br>Twiddled four trimmer pots, while viewing with a &apos;scope. It worked like an absolute champ.

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• CM

  @cmuller1441 · 2 years ago

  For the first simple schematic you should use a current source not a voltage buffer with a resistor. It&apos;s easy: just connect the feedback to in- to the point between the diode and the resistor.<br>This should already improve linearity.

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• MA

  @Manf-ft6zk · 2 years ago

  This is a good compensation circuit which reminds also of how to work with thermocouples to measure rf power by comparing it with dc power. It depends on finding matching couplers or the special matched dual coupler. &nbsp;<br>An alternative to transmit an analog signal with optocouples is to convert the analog signal with analog means to analog pwm, which can be in fact analog but looks of course very much digital and is not quite as fast as with the optocouples.

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• DI

  @Dieseleux · 2 years ago

  HCPL-7800 &nbsp;work well!

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• SA

  @Savan_Trivena · 2 years ago

  Your movies are thrilling like a crime. 😬

  1

• CN

  @cnvogel · 2 years ago

  Burr Brown ISO100 was a very fancy version of that scheme, in one huge ceramic package.

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• JA

  @JacquesMartini · 2 years ago

  &quot;Pro tips&quot; from the stone age! OMG! The two separate optocouplers are obsolete for decades! IL300 is friend if you REALLY wanne do it plain analog, which is still OK in many situations. Modern isolation amplifiers all work digital using a delta sigma converter on the input, transmitting digital (optical, inductive or capacitive) and converting back to analog using a filter. Works like a charm! If you REALLY learn something usefull, get an IL300 and play with it!

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• DA

  @darrylgodfrey9604 · 2 years ago

  Thank-you for this video - you unlocked something that was a mystery to me for some time.

• 4D

  @4DRC_ · 2 years ago

  Perfect timing! I was just pondering about isolated analog inputs the other day :D

• Y_

  @y_x2 · 2 years ago

  A IC like that IL300 was used in many telephone modem.