Initial commit: Piezoelectric circuits guide and backlog tasks

Add comprehensive guide covering:
- Zero-power crystal telephone (two piezos, no batteries)
- Amplified version with LM386
- Full-duplex intercom
- One-crystal walkie-talkie with PTT switching
- Rochelle salt crystal growing instructions
- Physics explanations and demonstration scripts

Backlog tasks created:
- task-1: Build Unpowered Crystal Telephone (high priority)
- task-2: Build One-Crystal Walkie-Talkie (medium priority)
- task-3: Grow Rochelle Salt Piezoelectric Crystals (medium priority)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backlog/config.yml

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+project_name: "Crystal Radio Project"
+default_status: "To Do"
+statuses: ["To Do", "In Progress", "Done"]
+labels: []
+milestones: []
+date_format: yyyy-mm-dd
+max_column_width: 20
+default_editor: "nvim"
+auto_open_browser: true
+default_port: 6420
+remote_operations: true
+auto_commit: false
+bypass_git_hooks: false
+check_active_branches: true
+active_branch_days: 30

backlog/tasks/task-1 - Build-Unpowered-Crystal-Telephone.md

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+---
+id: task-1
+title: Build Unpowered Crystal Telephone
+status: To Do
+assignee: []
+created_date: '2026-01-05 23:02'
+labels:
+  - hardware
+  - piezoelectric
+dependencies: []
+priority: high
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Build the zero-power piezoelectric crystal telephone that demonstrates the reversibility of the piezoelectric effect. Two crystals connected by wire - no batteries needed\!
+
+This project demonstrates:
+- Direct piezoelectric effect (sound → electricity)
+- Inverse piezoelectric effect (electricity → sound)
+- Energy flows both directions through the same crystal
+
+Refer to piezoelectric-circuits-guide.md for full instructions.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [ ] #1 Acquire 2x piezo discs (27mm or 35mm)
+- [ ] #2 Build acoustic couplers (funnels or cups)
+- [ ] #3 Solder wires between the two piezos
+- [ ] #4 Test communication at 1-3 meters
+- [ ] #5 Test maximum distance achievable
+- [ ] #6 Document results with photos/video
+<!-- AC:END -->

backlog/tasks/task-2 - Build-One-Crystal-Walkie-Talkie.md

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+---
+id: task-2
+title: Build One-Crystal Walkie-Talkie
+status: To Do
+assignee: []
+created_date: '2026-01-05 23:03'
+labels:
+  - hardware
+  - piezoelectric
+  - electronics
+dependencies: []
+priority: medium
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Build the half-duplex walkie-talkie that uses a SINGLE piezo crystal as both microphone AND speaker. Press PTT to talk, release to listen - demonstrating the ultimate reversibility of piezoelectricity.
+
+Key components:
+- LM386 amplifier
+- DPDT momentary switch (PTT)
+- Single piezo disc per unit
+- 9V battery power
+
+Refer to piezoelectric-circuits-guide.md Build 4 section.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [ ] #1 Source LM386 chips and support components
+- [ ] #2 Acquire DPDT momentary switches for PTT
+- [ ] #3 Build amplifier circuit on breadboard/perfboard
+- [ ] #4 Wire PTT switching logic
+- [ ] #5 Build enclosures (Altoids tins work great)
+- [ ] #6 Test two-unit communication
+- [ ] #7 Add TX indicator LED
+<!-- AC:END -->

backlog/tasks/task-3 - Grow-Rochelle-Salt-Piezoelectric-Crystals.md

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+---
+id: task-3
+title: Grow Rochelle Salt Piezoelectric Crystals
+status: To Do
+assignee: []
+created_date: '2026-01-05 23:03'
+labels:
+  - chemistry
+  - piezoelectric
+  - crystals
+dependencies: []
+priority: medium
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Grow piezoelectric crystals from kitchen ingredients (cream of tartar + baking soda). Rochelle salt has one of the strongest piezoelectric effects known\!
+
+This adds a "made from scratch" dimension to the crystal radio project - demonstrating that the piezoelectric property comes from the crystal structure itself, not manufacturing.
+
+Refer to piezoelectric-circuits-guide.md crystal growing section.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [ ] #1 Acquire cream of tartar (200g) and baking soda
+- [ ] #2 Make saturated Rochelle salt solution
+- [ ] #3 Grow seed crystals (3-7 days)
+- [ ] #4 Grow main crystal from seed (1-4 weeks)
+- [ ] #5 Apply electrodes (conductive paint or foil)
+- [ ] #6 Test piezoelectric response with LED/multimeter
+- [ ] #7 Compare to commercial ceramic piezo
+<!-- AC:END -->