Coin haptic timer

Timrrr — pocket haptic timer

Hey! Johno the human here. This repo/project is in part a test of the state of 'vibe electronics'. The board works but requires a minor bodge, bridging pins 6&7 on the ATtiny chip. Apart from that it works exactly as hopes! The goal is to train my 'time sense' and avoid taking logner-than-expected breaks. The whole process of this (apart from debugging the wrong pin during board bring-up) was smooth and pleasant, and I'm a little in awe of the fact that I could get 5 boards ASSEMBLED for $15, albeit with the new-customer $10 discount applied and a simple little circuit. Delightful times. Anyway, feel free to ask me about the project, or ask your agent about the project, but please don't ask your agent to ask me about the project! And if you want to replicate, well, maybe wait for v2, which I will make (and maybe sell?) if it turns out to be a useful device. Cheers, J.

Timrrr is a coin-sized timer that gives one discreet vibration approximately every five minutes. This repository captures the manufactured CR2032 MVP, its electrical reference files, firmware, assembly notes, and programming workflow.

Hardware snapshot

• 32 mm round, 0.8 mm PCB
• ATtiny412 microcontroller
• CR2032 primary cell
• Vybronics VCLP1020B002L 10 mm × 2.1 mm vibration motor, hand-soldered
• AO3400A low-side motor driver with flyback diode
• One red status LED
• Hard power switch; bridge the switch pads when the switch is omitted
• Single-wire UPDI programming through TP1–TP3

The intended final behavior is a 200 ms buzz every nominal five minutes. On power-up, one short LED flash means the open-circuit battery reading is acceptable and three flashes mean low battery. Normal periodic operation remains dark.

Current status — 2026-08-04

The as-fabricated PCB contains one confirmed pinout error: TP1 was routed to U1 physical pin 7 (PA3), but the ATtiny412's PA0/UPDI signal is physical pin 6. Bridging U1 pins 6 and 7 reworks the existing boards; PA3 is otherwise unused by the firmware. The editable PCB/netlist references have been corrected for the next revision, while the archived JLC manufacturing files remain unchanged.

After the rework, a CP2102 SerialUPDI adapter received STATUSA 0x20, the 32-byte tinyAVR SIB, and device signature 1E 92 23. The 476-byte bringup_led sketch was then programmed and verified successfully at 57600 baud, and its one-second LED pattern was observed on hardware. The 1652-byte pocket_haptic_timer sketch was subsequently programmed and flash-verified. Motor operation, five-minute RTC timing, ADC calibration, battery sag, and sleep current still require bench validation.

A second reworked board was subsequently programmed and flash-verified through the patched Raspberry Pi Pico Debug Probe toolchain with demo_10s_15s, which uses RTC standby sleep between a 10-second motor output and 15-second LED event.

Earlier debugging also identified a Raspberry Pi Debug Probe compatibility issue: its UART bridge suspends while DTR is low, whereas megaTinyCore SerialUPDI normally opens with DTR low. The retained DTR patch and standalone Pico probe remain useful diagnostic tools, but neither was the cause of the target silence; the incorrect physical UPDI pin was.

Repository map

• hardware/manufacturing/jlcpcb/as-received/ — original JLC order-detail downloads, unchanged.
• hardware/manufacturing/jlcpcb/order-export/ — extracted fabrication/order snapshot from JLC.
• hardware/source/ — KiCad electrical/reference files, BOMs, placement data, and explicit net audit.
• hardware/easyeda-import/ — historical EasyEDA import archive.
• firmware/bringup_led/ — first programming test; flashes the status LED once per second.
• firmware/motor_test/ — guarded two-second motor test.
• firmware/pocket_haptic_timer/ — Arduino-buildable five-minute timer; review-ready but not bench-qualified.
• firmware/baremetal_reference/ — original avr-gcc implementation retained for comparison.
• docs/programming.md — Pico/SerialUPDI wiring and Arduino IDE configuration.
• docs/assembly.md — motor, holder, and missing-switch connections.
• docs/cost_estimate.csv — original planning estimate.
• tools/pico/debugprobe.uf2 — Raspberry Pi Debug Probe firmware used during bring-up.
• tools/pico/updi_probe/ — read-only Pico firmware that generates UPDI locally without a USB-UART bridge.
• tools/serialupdi/ — Raspberry Pi Debug Probe compatibility patch for megaTinyCore SerialUPDI.

Important source-of-truth note

The files under hardware/source/ predate the final interactive EasyEDA routing and are retained as electrical and design-reference sources. The JLC order archive under hardware/manufacturing/jlcpcb/ is the authoritative record of the PCB that was actually fabricated.

First bring-up

Follow docs/programming.md. Program firmware/bringup_led/bringup_led.ino before installing the motor. A successful test gives a 250 ms LED flash once per second.

Do not connect a CR2032 while the Pico's 3.3 V output is connected to TP2. Do not run the motor from the Pico's 3.3 V rail.

Safety

A CR2032 can cause fatal internal burns if swallowed. Any enclosure must make the cell inaccessible to children and require a tool or two independent simultaneous actions to open. These files are an experimental MVP and have not received product-safety, EMC, or regulatory certification.