203 lines
11 KiB
Markdown
203 lines
11 KiB
Markdown
# kttl — Analog Control Prototype Wiring (LM35 sensor)
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Fully-analog temperature controller for a kettle, styled after a Soviet
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radiometer panel. No MCU: a comparator loop reaches/holds a rotary-selected
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target, a moving-coil meter shows live temperature on a **linear 0–100 °C
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dial**, and a solenoid-struck keyswitch clicks (Geiger-style) on each heater
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cycle.
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Sensor is an **LM35** (10 mV/°C, linear) — chosen so the dial is truly linear
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and the setpoint ladder is evenly spaced.
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> **Status:** prototype / paper design. A few values depend on measuring the
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> actual meter movement and solenoid — see *Open Unknowns*.
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---
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## 1. Panel controls
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| Ref | Control | Type | Function | Domain |
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|-----|--------------------|----------------------|-------------------------------------------|-------------|
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| SW1 | Rotary selector | 6-position, 1 wafer | Target temp tap (60/70/80/85/90/100 °C) | low-voltage |
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| SW2 | Rocker (on/off) | SPST | **Heater enable only** (not master power) | low-voltage |
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| SW3 | Hold toggle | SPDT | After target: HOLD (cycle) vs ONE-SHOT | low-voltage |
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| M1 | Moving-coil meter | µA/mA movement (М205)| Live temperature, linear 0–100 °C | always-on |
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Mains is live whenever plugged in. Electronics + meter sit on an **always-on
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rail**; the heater is gated downstream and switched only by the relay/SSR
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(mains-last). The rocker just **stops heating** — it is not a master cut-off.
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---
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## 2. Power tree
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```
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MAINS (live when plugged in)
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├─────────► PSU (mains→5V, always on) ──► +5V rail ─┬─► LM35, comparator, latch,
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│ │ meter driver, clicker logic
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│ └─► VREF_PRECISE (LM4040-2.5)
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│ → setpoint ladder
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│
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└─► HEATER PATH (mains): F1 fuse ─► TC1 thermal cutoff ─► K1/SSR1 ─► ELEMENT
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▲
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enable = SW2(rocker) AND logic-heat
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```
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**Note:** the ladder reference is now a **precision reference (not ratiometric)**
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because the LM35 output is an absolute voltage (10 mV/°C). The 5 V rail no longer
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needs to be accurate, but VREF_PRECISE does.
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---
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## 3. Schematic (block + signal level)
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```
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+5V (always on) VREF_PRECISE = 2.500V (LM4040-2.5)
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│ │
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┌──────┴──────┐ ┌────────┴────────┐
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│ LM35 │ OUT = 10mV/°C │ SETPOINT LADDER │
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│ Vs OUT GND│ (0°C=0V, 100°C=1.00V) │ R1..R7 (taps=°C)│
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└───┬───┬───┬──┘ └────────┬────────┘
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│ │ └─GND │ taps: 0.60/0.70/0.80/
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│ │ │ 0.85/0.90/1.00 V
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│ ├─────────────┬──────────────┐ ┌───────┴───────┐
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│ │ │ │ │ SW1 rotary 6-pos│
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[Rpd 18k │ │ └───────┬───────┘
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to GND] (to meter (to comparator −) │ common = selected Vref
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│ driver U3) │ R_in 10k │
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GND │ │ │
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▼ ▼ │
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┌──────────────────────┐ │
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│ U1 COMPARATOR LM393 │ │ Rf 2.4M
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│ (−) LM35 (+) tap │◄─┴──── hysteresis
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│ OUT ├──┬──── (to +) ~±1°C
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└──────────────────────┘ │
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OUT HIGH = cold │ on→off edge = "reached"
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(pull-up 10k to +5V) │
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┌──────────────────────────────┴──┐
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│ │
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▼ ▼
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┌──────────────┐ ┌────────────────┐
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│ U2 CD4013 │ │ CLICKER one-shot│
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│ D-FF latch │ │ → Q1 MOSFET │
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│ D=Hi │ │ → L1 solenoid │
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│ CLK=reached │ │ (+ D1 flyback)│
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│ CLR=POR + SW1│ │ strikes keyswitch│
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│ Q' ───┼──┐ └────────────────┘
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└──────────────┘ │
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▼
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SW3 HOLD ──────► ┌───────────────┐
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(HOLD: force Hi; │ ENABLE gate │
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1-SHOT: use Q') │ (AND) │
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└──────┬────────┘
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│ heater-want
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SW2 rocker (series)
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│
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▼
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┌──────────────┐
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│ Q2 ─► K1/SSR1│ switches MAINS to ELEMENT
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└──────┬───────┘ (via F1 + TC1, mains-last)
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▼
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ELEMENT
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METER BRANCH:
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LM35 OUT ─► U3 (op-amp + transistor current sink, Re) ─► M1
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I_meter = V_LM35 / Re (no offset: 0°C = 0V)
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linear 0–100 °C dial
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```
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---
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## 4. Component values
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### 4.1 Sensor — LM35
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- **U_LM35:** LM35 (or LM35DZ), Vs = +5 V, OUT = 10 mV/°C.
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- 0 °C → 0.000 V, 60 °C → 0.600 V, 100 °C → 1.000 V.
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- **Rpd:** ~18 kΩ from OUT to GND (lets the output pull down toward 0 V; basic
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LM35 only *sources* current). True 0 °C reading needs a negative rail; with a
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GND pull-down it reads reliably from ~+2 °C up — fine for a kettle.
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- Seal the sensor against water/steam (it's a 3-pin active part, not a bead).
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### 4.2 Precision reference + setpoint ladder
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- **VREF_PRECISE:** LM4040-2.5 (2.500 V shunt reference) + bias resistor from
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+5 V (e.g. ~2.7 kΩ). Absolute accuracy now matters (not ratiometric).
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- Ladder GND → 2.500 V; SW1 taps land on the LM35 setpoint voltages:
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| Ref | Segment | Calc. | Use (E96/std) |
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|-----|----------------------|---------|---------------|
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| R1 | GND → 60 °C (0.60 V) | 6.00 kΩ | 6.04 kΩ |
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| R2 | 60 → 70 °C | 1.00 kΩ | 1.00 kΩ |
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| R3 | 70 → 80 °C | 1.00 kΩ | 1.00 kΩ |
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| R4 | 80 → 85 °C | 0.50 kΩ | 499 Ω |
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| R5 | 85 → 90 °C | 0.50 kΩ | 499 Ω |
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| R6 | 90 → 100 °C | 1.00 kΩ | 1.00 kΩ |
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| R7 | 100 °C (1.00 V) → ref| 15.0 kΩ | 15.0 kΩ |
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| RT | master cal trim | — | 500 Ω 10-turn (series w/ R7) |
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Ladder current ≈ 100 µA. Setpoint voltages = temp × 10 mV/°C — clean and even.
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### 4.3 Comparator + hysteresis
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- **U1:** LM393. LM35 OUT → (−); SW1 tap → (+) via **R_in = 10 kΩ**.
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OUT HIGH = cold = heater wanted. Pull-up 10 kΩ on OUT to +5 V.
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- **Rf:** 2.4 MΩ from OUT to (+) → maintain band ≈ ±1 °C (R_in/Rf · Vout_swing).
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Band varies slightly with selected tap impedance.
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### 4.4 Mode latch (one-shot vs hold)
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- **U2:** CD4013 D flip-flop. D = HIGH. CLK = comparator on→off ("reached") edge
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(RC-debounce if it chatters). CLR = power-on-reset cap **and** SW1 common
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(changing temp re-arms). Q′ → enable gate.
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- **SW3 (Hold):**
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- HOLD → forces enable gate's 2nd input HIGH (latch bypassed → cycles forever).
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- ONE-SHOT → enable uses Q′ (heater latches OFF after first reach).
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- Wire SW3 to also pulse CLR so flipping to HOLD resumes cycling.
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### 4.5 Heater drive
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- Enable gate (heater-want) AND **SW2 rocker** (series) → **Q2** (small MOSFET) →
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relay coil **K1** (with flyback diode) *or* **SSR1** control input.
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- K1/SSR1 switches mains to the element, downstream of **F1 (fuse)** and **TC1
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(independent thermal cutoff)**.
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### 4.6 Clicker
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- Comparator on→off edge → one-shot pulse → **Q1** (logic-level MOSFET) → **L1**
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mini push-pull solenoid (5 V, ~3.5 mm stroke, Adafruit 2776 class) + **D1**
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flyback diode. Plunger strikes a tactile keyswitch (switch gives the click +
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bump; pick the strike target/resonator for pitch).
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- HOLD → ticks each maintain cycle; ONE-SHOT → single tick. Add jitter to the
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pulse for Geiger-style randomness instead of metronomic ticking.
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### 4.7 Meter driver
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- **U3:** op-amp + transistor current sink. LM35 OUT → op-amp (+); meter in the
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collector/drain; Re in emitter/source. `I_meter = V_LM35 / Re`, independent of
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coil resistance. **No offset stage** (0 °C already = 0 V).
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- Re by movement: **1 mA → Re = 1.00 kΩ**; **100 µA → Re = 10.0 kΩ**.
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- Dial is **linear 0–100 °C** — re-letter the М205 face 0→100.
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---
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## 5. Safety notes
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- **SW1/SW2/SW3 are all low-voltage.** No panel switch carries element current;
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mains is switched only by K1/SSR1 (mains-last).
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- **F1 fuse + TC1 thermal cutoff in series with the element are mandatory.** The
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comparator/latch is *control*, not *protection* — it can't save you from a
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welded relay or a failed/detached sensor.
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- **Always-on rail = always-live internals.** True off is unplugging; the rocker
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only stops heating.
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- Keep the meter/logic rail decoupled from heater switching transients, or the
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needle twitches and the latch can glitch each cycle.
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---
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## 6. Open unknowns (measure before committing values)
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1. **М205 movement:** full-scale current and coil resistance — sets Re. Measure
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first; guess wrong and the needle pins or barely moves.
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2. **Solenoid force/stroke** vs the chosen keyswitch (~0.5 N, ~2 mm): confirm
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force *at* the working stroke (not headline force) and intermittent duty at
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the fastest click rate (near boil).
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3. **LM35 low-end:** reads down to ~+2 °C with a GND pull-down; true 0 °C needs a
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negative supply. Decide if that matters for the dial's bottom mark.
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4. **Sensor sealing/placement:** the LM35 must be waterproofed; element-mounted
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(fast, overshoots) vs water-immersed (accurate, laggy) changes hysteresis feel.
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5. **VREF_PRECISE accuracy** now sets setpoint accuracy directly (no ratiometric
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cancellation) — use a ≤0.5% reference and the master trim RT to null offset.
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```
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