Gavin DeGuire

Electronics Skill Tree — Gavin

SKILL TREE

ROADMAP

Project Roadmap

Current and near-term builds ordered by dependency and impact. Each phase represents a coherent batch of work that unlocks the next. Skipped or collapsed tiers from the skill tree are noted.

Active now

Next up — unblocked

Soon — 1 blocker

Later

PHASE 0Anchor — Complete ✓

DS1052E repair done. Running continuously on both channels at 50MHz. Staying at 50MHz — no unlock needed for current work.

Rigol DS1052E — working ✓

Both channels confirmed stable. 50MHz sufficient for all synth, PSU, and audio-band work. Anchor is live and validating downstream builds.

Complete — unblocks all downstream calibration

PHASE 1PSU — Unlock Split Rail

Parts list shows 19.5V laptop bricks on hand. That's your LM317/337 input — no purchase needed. This unblocks all op-amp work.

LM317/337 ±15V linear PSU

Use 19.5V Dell/HP brick (owned). Bridge rectifier → 4700µF 35V filter caps → LM317/337. Dual-rail ±15V out. All ICs in hand.

19.5V bricks in hand — $0 input cost

CC/CV error amp loop

TL072 error amp around pass transistor. 0–1.5A current limit. Unlocks safe prototyping of synth modules. Skip tier: ICL7660 split supply already working for op-amp breadboard.

PHASE 2Synth — Fix Current Build + 555 VCO

HC14 drone is breadboarded. Two fixes needed before moving on. 555 VCO is unblocked as a parallel track.

HC14 drone: replace coupling caps

22µF → 1000µF output coupling caps across all 5 channels. Fix broken speaker lead. Verify AC coupling bias on all channels (gate → 1kΩ → 10µF → pin3, 100kΩ to GND).

555 VCO (CV-controlled)

NE555 astable with CV input resistor. Not V/oct accurate but teaches V-to-F fundamentals directly. NE555 in transit.

PHASE 3WF Gen — Debug + Output Stage

AD9833 + amplitude/offset stages breadboarded and powered. Signal chain fault somewhere after AD9833 output — under active debug. Most likely cause: TL072 single-rail biasing. Fix: add ICL7660 split supply to breadboard first.

Debug signal chain fault

Probe each stage with Rigol in sequence: AD9833 VOUT → filter output → after pot → final TL072 output. First railed or dead node is the fault. Root cause likely missing 2.5V bias on TL072 non-inverting inputs (single-rail operation).

Fix: add ICL7660+MT3608 split supply to breadboard — all owned

Sallen-Key reconstruction filter

2nd-order LPF at ~100kHz (TL072 + passives, all in hand). Removes DAC staircase artifacts. THD: ~−40dBc → ~−65dBc. Most impactful single upgrade.

Encoder UI (Pico + ST7789V)

KY-040 encoder (owned) + ST7789V (in transit). Coarse/fine frequency. Waveform toggle. Feels like an instrument.

PHASE 4Scope — Build + Audio FFT

Pico audio scope + Pi FFT is the highest-ratio DIY instrumentation available to you. MCP3202 + ST7789V already on the way.

Pico dual-core scope (80–100ksps)

Core 0 samples MCP3202, core 1 drives ST7789V. 40kHz usable BW, 12-bit. Full audio band. Level trigger + pre-trigger buffer. Waiting on MCP3202 + ST7789V arrival.

Waiting: MCP3202 + ST7789V in transit

Pi 3 FFT spectrum analyzer

NumPy FFT on incoming Pico sample buffers → HDMI display. Real-time spectrum to 40kHz. Invaluable for synth harmonic analysis. $0 marginal cost. Skip: serial plotter tier is a waste of time given you have an Uno already confirming ADC wiring.

$0 — Pi 3 already owned

Input protection + buffered front end

Resistor divider, 1N4148 clamping, AC/DC coupling. OPA2134 or AD8065 unity-gain buffer. BNC jack. Makes the scope safe to probe real circuits.

Gap: OPA2134/AD8065, BNC jack

PHASE 5LCR Meter — High DIY Ratio

Underrated build. AD9833 excitation + bridge + TL072 detector hits 1% accuracy for ~$20 and competes with $80–200 commercial units. Directly useful for synth component selection.

AD9833 excitation bridge

Reuse WF gen AD9833 as excitation source. Known-value reference arm. TL072 differential detector. Sweeps frequency to find L and C from phase/magnitude response.

Auto-ranging LCR + display

CD4051 mux for range switching. MCP3202 ADC for measurement. ST7789V display. Measures L, C, R, Q factor, ESR. All ICs in hand except precision references.

Gap: 0.1% references, LM4040

PHASE 6Frequency Counter

Best DIY ratio of any instrument. TCXO-referenced Pico PIO counter hits 7–8 digit accuracy for ~$10–15 and competes with $200–400 commercial units.

Pico PIO gate counter

LM393 squarer (owned) + Pico PIO frequency counter. 1Hz–50MHz. 7-digit display on ST7789V. Gate time from 10ms (fast) to 1s (accurate). All hardware in hand.

$0 marginal — all parts owned

TCXO reference upgrade

Replace Pico crystal with external TCXO (±2ppm, ~$3 AliExpress). Pushes accuracy to 7–8 digits reliably. Essential for V/oct VCO calibration verification.

PHASE 7Synth — Expo VCO + Filter

Requires Phase 1 PSU + Phase 0 scope. The main signal chain build. Expo converter → VCO → VCF → VCA.

Expo converter (matched NPNs)

Hand-matched 2N3904 pair (200 on hand) or THAT340. 0.1% precision resistor ladder. TL072 buffer. Foundation of V/oct tracking. Skip: 555 VCO is sufficient to learn V-to-F before needing true expo.

Gap: 0.1% resistors (Mouser)

TL072 integrator VCO

Integrator driven by expo converter current. Triangle + square outputs. 3296W 25-turn trimmers for V/oct calibration. Calibrate against WF gen + DS1052E simultaneously.

LM13700 OTA VCF + VCA

OTA as voltage-controlled filter and VCA. CV-controlled cutoff. Resonance via feedback. AR envelope generator. Complete gated voice.

PHASE 8PCB Consolidation — KiCad → JLCPCB

After breadboard validation of each instrument, consolidate to fabricated PCBs. Scope PCB unlocks the high-frequency ADC path. Synth PCB is the final deliverable.

Scope PCB v1

Tier 4 circuit on 2-layer KiCad with GND plane. 10–20Msps vs 5Msps on breadboard. Unlocks AD9288 FPGA path.

WF Gen PCB v1

AD9833 + filter bank + amplitude on 2-layer KiCad. SMD 0402/0603. SMA output. Clean above 5MHz.

Full Voice PCB (VCO+VCF+VCA)

Complete synth voice on fabricated PCB. LEGO enclosure. Panel jacks for CV, gate, audio out.

TIERS INTENTIONALLY SKIPPED / COLLAPSED

Scope T0 (serial plotter): You already have Uno + breadboard confirming ADC wiring. Skip to Pico dual-core directly.
PSU T0 (USB only) + T1 (ICL7660): ICL7660 split supply already working. Collapse into: go straight to LM317/337 with owned 19.5V bricks.
MM T0–T1 (Uno ADC, LM4040 basic): DT-926 covers basic DC voltage. Skip to the 12-bit MCP3202 DVM once MCP3202 arrives.
WF Gen T0 (raw AD9833 only): You've already proven the DDS concept. The output stage is the next real step.
Synth T0 → T1 (HC14 → 555): Keep HC14 drone as a parallel exploration but don't treat it as a prerequisite gate for 555 VCO work.