Monitors speaker power LED via LDR + comparator. When LED goes OFF → wake from sleep → servo presses Fingerbot → wait for boot → sleep.
- PC2 (pin 19): Trigger input (comparator OUT + manual button, shared via R8 10K)
- PA5 (pin 6): Servo PWM (TCA0 WO5)
- PB2 (pin 14): TX (debug serial, TX-only)
| LDR based comparator | Microcontroller | Board Top (Combined) | Board Bottom (Combined) | 3D Render of PCB |
|---|---|---|---|---|
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Note
SCHEMATIC (V-1.0)
Tip
Check below, towards the end, for a better version with more current saving (aka improved battery life)
| Board bottom view | Board top view | Side view | Angled view |
|---|---|---|---|
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- megaTinyCore: https://github.com/SpenceKonde/megaTinyCore
- Servo library:
#include <Servo_megaTinyCore.h>(NOT<Servo.h>) Reason: As Described here
- IDE: Arduino IDE 2.3.8
- UPDI programmer: Could your homebrewed one, but I used and followed instructions from this one
┌───────────────────────────────────────────────────────────────────┐
│ SETUP │
│ ───── │
│ 1. disableSerialPins() // TX/RX driven LOW │
│ 2. disableUnusedPins() // unused pins → INPUT_PULLUP │
│ 3. ADC0.CTRLA &= ~ADC_ENABLE_bm // disable ADC │
│ 4. SPI0.CTRLA &= ~SPI_ENABLE_bm // disable SPI │
│ 5. setupTriggerPin() // PC2 edge interrupt │
│ 6. servo.attach(PA5) │
│ 7. servo.write(SERVO_REST) │
│ 8. delay(500) // let servo settle │
│ 9. servo.detach() // stop PWM, save power │
│ 10. sei() // enable global interrupts │
│ 11. set_sleep_mode(SLEEP_MODE_PWR_DOWN) │
│ 12. sleep_enable() │
└──────────────────────────────┬────────────────────────────────────┘
│
▼
ENTER LOOP
┌─────────────────────────────────────────────────────────────────┐
│ LOOP START │
│ ────────── │
│ - Clear any pending interrupt flags │
│ - sleep_cpu() │
│ - ... MCU stops here, draws ~1-5µA ... │
└──────────────────────────────┬──────────────────────────────────┘
│
Speaker turns OFF (LED OFF)
OR manual button pressed
→ Edge on PC2 triggers ISR
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ ISR(PORTC_PORT_vect) │
│ ──────────────────── │
│ - flags = VPORTC.INTFLAGS // fast read │
│ - PORTC.INTFLAGS = flags // clear flags │
│ - triggered = 1 // set flag for main loop │
│ - (ISR exits, loop resumes after sleep_cpu) │
└──────────────────────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ 1. WAKE CHECK │
│ - if (!triggered) → back to sleep (spurious wake) │
│ - triggered = 0 │
│ - #ifdef DEBUG_ENABLED: Serial.begin(115200) │
└──────────────────────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ 2. DEBOUNCE │
│ - delay(50ms) │
│ - Re-read PC2 actual state │
│ - isValidTrigger(): │
│ Current module: valid if PC2 == HIGH (LED OFF) │
│ Our PCB: valid if PC2 == LOW (LED OFF) │
│ - If NOT valid → false trigger → skip to step 6 (sleep) │
└──────────────────────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ 3. DISABLE INTERRUPT │
│ - PORTC.PIN2CTRL &= ~PORT_ISC_gm │
│ - PC2 edges now ignored │
│ - Prevents re-trigger during speaker boot LED dance │
└──────────────────────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ 4. SERVO PRESS │
│ - servo.attach(SERVO_PIN) │
│ - servo.write(SERVO_PRESS) // press position │
│ - delay(200ms) // hold press │
│ - servo.write(SERVO_REST) // release │
│ - delay(200ms) // settle │
│ - servo.detach() // stop PWM, save power │
└──────────────────────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ 5. FIXED WAIT │
│ - delay(8000) // 8 seconds │
│ - Speaker boots, LED does dance, we ignore it all │
│ - Interrupt is disabled so no re-triggers │
└──────────────────────────────┬──────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ 6. RE-ENABLE + CLEANUP + SLEEP │
│ - PORTC.PIN2CTRL = PORT_ISC_xxxx_gc // re-enable edge │
│ - PORTC.INTFLAGS = PIN2_bm // clear pending │
│ - #ifdef DEBUG_ENABLED: │
│ Serial.flush() │
│ Serial.end() │
│ disableSerialPins() │
│ - (loop restarts → sleep_cpu) │
└──────────────────────────────┬──────────────────────────────────┘
│
▼
BACK TO LOOP START
(sleep)
| Case | What Happens |
|---|---|
| Power-on with speaker already OFF | No edge = no ISR. User presses button to trigger manually. |
| False trigger (noise) | Wake → debounce → re-read shows LED ON → skip action → sleep |
| LED blinks during boot | Interrupt disabled during wait, no re-triggers |
| Button pressed during wait | Interrupt disabled, ignored |
| Speaker fails to turn on | We waited 8s anyway, go to sleep. Next OFF event retries. |
// Debug output over serial (TX-only, 115200 baud)
// Comment out for production to save power
#define DEBUG_ENABLED
// Trigger polarity - depends on which LDR module you're using:
// true = off-shelf test module (PC2 HIGH when LED OFF)
// false = our custom PCB (PC2 LOW when LED OFF)
#define INVERT_TRIGGER true
// Servo positions in degrees - calibrate for your Fingerbot setup
#define SERVO_REST 90 // Resting position (not touching button)
#define SERVO_PRESS 45 // Press position (pushing Fingerbot button)
// Timing in milliseconds
#define DEBOUNCE_MS 50 // Wait after wake before validating trigger
#define PRESS_HOLD_MS 1000 // How long servo holds the press position
#define PRESS_SETTLE_MS 1000 // Wait for servo to return to rest before detach
#define SERVO_INIT_MS 1000 // Initial servo settle time at boot
#define BOOT_WAIT_MS 8000 // Wait for speaker boot (covers LED dance)| Module | LED ON | LED OFF | Trigger Edge |
|---|---|---|---|
| off-shelf (Test Module) | PC2 LOW | PC2 HIGH | RISING |
| Our PCB | PC2 HIGH | PC2 LOW | FALLING |
Use
#define INVERT_TRIGGER truefor Test module.
Test sketches live in tests/ folder. Use these before running the main firmware.
attiny1607_speaker_led_behaviour_test.ino
Purpose: Observe and analyze the speaker LED behavior (the "dance" pattern during boot).
Use this to:
- Verify your LDR/comparator circuit is detecting LED state changes
- Measure the speaker's startup LED timing
- Determine the correct
BOOT_WAIT_MSvalue
Hardware:
- PC2 (pin 19) → Comparator OUT
- PB2 (pin 14) → TX to serial adapter RX
Usage:
- Upload the sketch
- Open serial monitor at 115200 baud
- Turn speaker ON/OFF and observe output
Example output:
LED Analyzer started
Initial: ON
[1523] OFF (was ON 1523ms)
[1842] ON (was OFF 319ms)
[2105] OFF (was ON 263ms)
[2389] ON (was OFF 284ms)
[8245] OFF (was ON 5856ms) ← longest ON = solid period
Reading the output:
[elapsed_ms]= time since sketch startedON/OFF= current LED state (as seen by comparator)(was STATE duration)= previous state and how long it lasted
The longest ON duration before a final OFF tells you how long the LED stays solid after the boot dance. Set BOOT_WAIT_MS to be longer than this.
So. after assembly of the board adn uploading the program, found out that the idle current consumption of the system is around 2.5 mA and the peak, when the servo is active, is around 12 mA. So, even though we picked low current comparator, put our micro to deep sleep and all that, we will have an av. battery life of a month (if we are lucky) based on the following ...
| State | Current | Duration/day |
|---|---|---|
| Sleep (servo connected) | ~2.5 mA | ~23.9 hrs |
| Wake + servo active | ~12 mA | ~0.1 hrs (5 triggers × ~1.2 min each) |
(2.5 mA × 23.9 hr) + (12 mA × 0.1 hr) = 59.75 + 1.2 ≈ 61 mAh/day
1500 mAh / 61 mAh/day ≈ 24-25 days
But with the servo disconnected, we found out that the current consumption is very low, in deep-sleep.
- Deep Sleep state: 0.1 mA (100µA) (Of-course, there's room for improvement there too)
Add a low power MOSFET to control servo's power lines ...
WIP
VCC (3V) ───┬─────────── Servo VCC (red)
│
[SOURCE]
│
MCU ──┬──[GATE] SI2301 (P-FET)
(PA6) │ │
R1 [DRAIN]
10k │
│ └─────────── Servo VCC
GND
Servo GND ──────────────── GND
Servo SIG ──────────────── PA5 (existing)
Tip
👉🏻 attiny1607_speaker_fingerbot_v2 (NEW)
