Lazy Sunday afternoon project, a simple *PC817 OptoCoupler tester.
Two very simple ~5V circuits:
1) Quick check — push the button, LED on = works.
2) Test Circuit as mentioned in the datasheet for frequency / pulse behavior test.
Nothing fancy, but handy for sorting out good vs questionable parts.
Blog:
https://togo-lab.io/?p=153
Gitea:
https://gitea.togo-lab.io/tgohle/0002-PC817-Series-PhotoCoupler-Tester
Finally got around to editing video of my experiments in improving response times of slow low-cost #optocoupler #optoisolator ICs such as the #PC817
https://youtu.be/s1l86nTIWEE
The improved speed was sufficient to pass #MIDI data (31250 bits/s) through it
@mike805
I tried the #cascode #amplifier trick with the PC817 #optocoupler. IMSAI Guy only showed how the voltage of the transistor base affects the speed of the falling edge. But notice how the rising edge remains largely unaffected.
By comparison, the common mode NPN #transistor amplifier with 150 ohm resistor across base-emitter, yielded noticeably sharper rising/falling edges
#electronics #oscilloscope
@mike805
[IMSAI Guy] explains the cascode amplifier trick
https://youtu.be/APUhm2tsCiE
See Figure 13 High bandwidth optocoupler configuration
https://www.onsemi.com/pub/Collateral/AND8273-D.PDF
I might need to try that for comparison
Testing the switching characteristics of cheapo PC817 optocouplers from Ebay.
555 timer astable is generating a 37kHz square wave test input.
Rise/fall time is way out of spec for use in #MIDI. But the recommended component, 6N138, is much more expensive.
Instead have the #optocoupler drive the base of an NPN #transistor and by adding appropriate resistors, I get much improved switching speeds. Is this good enough for a MIDI input circuit? #electronics #oscilloscope #breadboard
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