add reference files for new skill legacy-circuit-mockups

skills/legacy-circuit-mockups/references/breadboard.md

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+# Solderless Breadboard
+
+A practical Markdown specification and reference for **common solderless breadboards**, intended for electronics prototyping, education, and hobbyist development.
+
+---
+
+## 1. Overview
+
+A **solderless breadboard** is a reusable prototyping platform that allows electronic components to be interconnected without soldering. Connections are made via internal spring clips.
+
+### Typical Uses
+
+* Rapid circuit prototyping
+* Educational labs
+* Logic and microcontroller experiments
+* Low-power analog and digital circuits
+
+### Not Suitable For
+
+* High current (>1A)
+* High voltage (>36V)
+* RF / high-frequency designs
+* Vibration-prone or permanent installations
+
+---
+
+## 2. Physical Construction
+
+### Materials
+
+* ABS or polystyrene body
+* Phosphor bronze or nickel-plated spring contacts
+* Adhesive backing (optional)
+
+### Standard Hole Pitch
+
+* **2.54 mm (0.1 in)** - compatible with DIP ICs and standard headers
+
+### Contact Characteristics
+
+| Parameter          | Typical Value |
+| ------------------ | ------------- |
+| Contact resistance | 10-50 mΩ      |
+| Insertion cycles   | ~5,000        |
+| Wire gauge         | 20-28 AWG     |
+
+---
+
+## 3. Internal Electrical Connections
+
+### Terminal Strips (Main Area)
+
+* Rows of **5 interconnected holes**
+* Horizontal connectivity
+* Center trench isolates left and right halves
+
+```
+A B C D E | F G H I J
+──────────┼──────────
+Connected | Connected
+```
+
+### Power Rails
+
+* Vertical buses on each side
+* Often **split in the middle** (not always continuous)
+* Usually marked **red (+)** and **blue (-)**
+
+```
++  +  +  +  +   (may be split)
+-  -  -  -  -
+```
+
+> ? Always verify continuity with a multimeter
+
+---
+
+## 4. Common Breadboard Sizes
+
+| Type      | Tie Points | Typical Use              |
+| --------- | ---------- | ------------------------ |
+| Mini      | 170        | Small test circuits      |
+| Half-size | 400        | Microcontroller projects |
+| Full-size | 830        | Complex prototypes       |
+| Modular   | Variable   | Expandable systems       |
+
+---
+
+## 5. Component Compatibility
+
+### Compatible Components
+
+* DIP ICs (300 mil, 600 mil)
+* Axial resistors and diodes
+* LEDs
+* Tactile switches
+* Jumper wires
+* Pin headers
+
+### Problematic Components
+
+| Component            | Issue                      |
+| -------------------- | -------------------------- |
+| TO-220               | Too wide / stress contacts |
+| SMD                  | Requires adapter           |
+| Large electrolytics  | Mechanical strain          |
+| High-power resistors | Heat                       |
+
+---
+
+## 6. Electrical Characteristics
+
+### Typical Limits
+
+| Parameter           | Recommended Max    |
+| ------------------- | ------------------ |
+| Voltage             | 30-36 V            |
+| Current per contact | 500-1000 mA        |
+| Frequency           | <1 MHz (practical) |
+
+### Parasitics (Approximate)
+
+| Type        | Value               |
+| ----------- | ------------------- |
+| Capacitance | 1-5 pF per node     |
+| Inductance  | 10-20 nH per jumper |
+
+---
+
+## 7. Best Practices
+
+### Power Distribution
+
+* Run **ground and Vcc** to both sides
+* Bridge split power rails if needed
+* Decouple ICs with **0.1µF ceramic capacitors**
+
+### Wiring
+
+* Keep wires short and tidy
+* Use color coding:
+
+  * Red: Vcc
+  * Black/Blue: GND
+  * Yellow/White: Signals
+
+### IC Placement
+
+* Place DIP ICs **straddling the center trench**
+* Avoid forcing pins
+
+---
+
+## 8. Common Mistakes
+
+| Mistake                       | Result             |
+| ----------------------------- | ------------------ |
+| Assuming rails are continuous | Power loss         |
+| Long jumper wires             | Noise, instability |
+| No decoupling capacitors      | Erratic behavior   |
+| Exceeding current limits      | Melted contacts    |
+
+---
+
+## 9. Testing & Debugging
+
+### Continuity Check
+
+* Verify rails and rows using a multimeter
+
+### Signal Integrity Tips
+
+* Avoid breadboards for:
+
+  * High-speed clocks
+  * ADC precision circuits
+
+---
+
+## 10. Typical Breadboard Layout Example
+
+```
+[ + ] [ - ]   Power Rails
+[ + ] [ - ]
+
+ A B C D E | F G H I J
+ A B C D E | F G H I J
+ A B C D E | F G H I J
+```
+
+---
+
+## 11. Accessories
+
+| Item                    | Purpose           |
+| ----------------------- | ----------------- |
+| Jumper wire kits        | Connections       |
+| Breadboard power module | 5V / 3.3V supply  |
+| Adhesive base           | Mounting          |
+| Logic probe             | Digital debugging |
+
+---
+
+## 12. Reference Links
+
+* [https://en.wikipedia.org/wiki/Breadboard](https://en.wikipedia.org/wiki/Breadboard)
+* [https://learn.sparkfun.com/tutorials/how-to-use-a-breadboard](https://learn.sparkfun.com/tutorials/how-to-use-a-breadboard)
+* [https://www.allaboutcircuits.com/technical-articles/using-a-breadboard/](https://www.allaboutcircuits.com/technical-articles/using-a-breadboard/)
+
+---
+
+**Document Scope:** Solderless breadboard reference
+**Audience:** Hobbyist, student, engineer
+**Status:** Stable reference