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initial README

README.md

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+# PC817 Series PhotoCoupler Tester
+
+Simple test setup for the **PC817 optocoupler family**.  
+Goal: quick validation of parts and basic frequency response.
+
+## Project Scope
+- **Part check**: Verify if a single PC817 is functional (on/off behavior).
+- **Frequency response**: Measure switching speed with an external signal source (Siglent arbitrary generator) and scope.
+
+## Notes
+- Two independent circuits:  
+  1. **Basic LED–Transistor test** for functionality.  
+  2. **Frequency response test** for rise/fall times and cutoff.
+- This repo contains only the **blueprints and notes**.  
+  No final PCB or kit planned.
+
+## Status
+Planned as a short **8h project** → quick results only.  
+A detailed write-up may follow on the Tōgō-Lab blog.
+