Precision Digital Timer for AC Appliance Control
Compact, microcontroller-based digital timer for reliable automatic ON/OFF control
Open-Source Hardware (CERN-OHL-S v2)
⚠️ Commercial Notice: Commercial manufacturing, resale, or distribution requires permission.
Copyright (c) EmptyIdea / Sai Innovation
- Contact: rk@saiinnovation.com
- Website: emptyidea.in
Multipurpose Timer Lite-A - Professional AC Appliance Control Solution
The Multipurpose Timer Lite-A is a versatile, high-precision timing solution designed for various industrial and home automation applications. This open-source hardware project includes the complete design files, firmware, and documentation for building and customizing the timer.
The timer features a bright 4-digit LED display, intuitive two-button interface, and a robust relay output for controlling appliances. It supports dual operation modes: Manual Timer Setting and Auto Learn Mode, allowing you to either set a custom countdown time manually or "teach" the timer a specific duration by running a task once.
The device is engineered to handle wide mains voltage fluctuations and frequent power interruptions, making it particularly suitable for Indian electrical conditions, including:
- Wide mains voltage fluctuations
- Frequent power interruptions
- Inductive load environments commonly found in India
- ✅ Dual Operation Modes: Manual Timer Setting & Auto Learn Mode
- ✅ Wide Voltage Range: 100-240V AC input support
- ✅ High Reliability: Non-volatile memory preserves settings
- ✅ User-Friendly: Intuitive two-button interface
- ✅ Robust Design: Built for challenging electrical environments
Front View |
Back View |
Side View |
Display Close-up |
Transparent Case View |
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⚠️ Code Repository Notice
This repository contains testing code for the hardware.
The code provided here is not the latest version. The actual latest source code was written in Mount River Studio. If you need access to the latest source code, please contact us at rk@saiinnovation.com.
- Manual Timer Setting: Set a custom countdown time manually
- Auto Learn Mode: "Teach" the timer a specific duration by running a task once
Adjustable countdown duration from 1 minute to 48 hours, suitable for both short-cycle and long-duration applications.
4-digit, 7-segment LED display with auto-brightness for excellent readability under low-light as well as bright outdoor conditions.
Internal non-volatile memory retains the last configured timer value and system settings after power loss.
Integrated buzzer for audible feedback (clicks and alarms).
10A relay output for AC appliance control (up to 2500 VA), with PWM-assisted relay drive that improves switching efficiency, reduces contact stress, and increases overall relay service life.
Two-button control (MENU and START) with short and long press functions, designed for simple and error-free operation. Long-press button logic prevents accidental operation.
- Countdown timer duration — Set from 1 minute to 48 hours
- Display brightness adjustment — 7 levels of brightness control
- Display auto-sleep timeout — Power-saving display management
Ability to pause and resume active timer cycles, providing flexible control during operation.
- Surge-protected AC input — Protection against voltage spikes
- Snubber network — Reliable inductive load switching and EMI reduction
- Watchdog timer — System stability protection
- Non-blocking architecture — Responsive operation without delays
| Parameter | Specification |
|---|---|
| Model Number | EIMPTLA10A |
| Input Supply Voltage | 100 – 240 V AC |
| Input Current | Approx. 0.01 A |
| Output Switching Voltage | 230 – 250 V AC |
| Maximum Switching Current | 10 A |
| Maximum Continuous Current | 15 A |
| Maximum Output Power | 2500 VA |
| Relay Mechanical Life | Up to 100,000 operations |
| Microcontroller | CH32V003 |
| Display | 4-digit 7-segment (TM1650 via I2C) |
Multipurpose Timer Lite-A/
├── Code/
│ └── multiPurposeTimer_Basic_V1/
│ └── multiPurposeTimer_Basic_V1.ino # Arduino firmware (testing code)
├── PCB/
│ └── Multipurpose Timer V1.0/
│ ├── Multipurpose Timer V1.0.kicad_pcb # PCB layout
│ ├── Multipurpose Timer V1.0.kicad_sch # Schematic
│ ├── Multipurpose Timer V1.0.kicad_pro # KiCad project
│ └── shapes3D/ # 3D component models
├── Case/
│ ├── Multipurpose Timer Case V2_3D_Print.3mf # 3D printable enclosure
│ └── README.txt # MakerWorld link and license info
├── Docs/
│ ├── Product Manual.md # Complete user manual
│ └── images/ # Manual images
├── LICENSE # CERN-OHL-S v2 license
└── README.md # This file
📦 3D Enclosure Available on MakerWorld: The 3D printable enclosure is available for public use on MakerWorld. See
Case/README.txtfor the direct link and license information.
- Borewell pumps
- Overhead tank filling systems
- Domestic and agricultural irrigation pumps
- Outdoor and garden lighting
- Signboard and shop lighting
- Street and security lighting (within relay rating)
- Exhaust fans and ventilation systems
- Geysers and heaters (within relay rating)
- Decorative and seasonal lighting
- Electrical control panels
- Machine timing and process delays
- Warm-up and cool-down timing
- Equipment power cycling
- Test bench timing control
- Timed operation of tools and instruments
✅ Compatible Loads: Suitable for both resistive and inductive loads due to built-in snubber protection
⚠️ High-Power Applications: For high-power motors or heavy industrial loads, use the timer to drive an external contactor or relay
⚠️ Installation Verification: Always verify load current, voltage, and duty cycle before installation
Before you begin, ensure you have the following:
- Arduino IDE or compatible development environment
- CH32V003 development board or compatible hardware
- KiCad 9.0 or later (for PCB design files)
- 3D printer (for enclosure, optional)
- Open
Code/multiPurposeTimer_Basic_V1/multiPurposeTimer_Basic_V1.inoin Arduino IDE - Install required libraries:
- Wire (usually included with Arduino)
- CH32V003 board support package
- Select the appropriate board and port
- Upload the firmware to your device
Refer to the Product Manual for detailed wiring diagrams, terminal layouts, and installation instructions.
⚠️ WARNING – RISK OF ELECTRIC SHOCK
- Always disconnect mains power before installation or maintenance
- This product operates directly on AC mains voltage
- Installation must be performed by a qualified electrician or trained technician
- Incorrect wiring may result in electric shock, fire hazard, or permanent damage
| Operating State | Display |
|---|---|
| Idle | Set time (e.g., 20.00 = 20 minutes) |
| Running | Remaining countdown time |
| Paused | PAUS (flashing) |
| Menu Mode | MENU, TIME, AUTO, BRGT |
- Set Timer: Long-press MENU button to enter menu, navigate to TIME option, and adjust duration (1 minute to 48 hours)
- Start Timer: Long-press START button to begin countdown
- Pause/Resume: Long-press START button during operation
- Stop Timer: Short-press START button to stop and return to idle
To enter the Menu, Long Press (1s) the Menu Button while in Idle state. The display will show "MENU".
Menu Options:
- TIME (Manual): Set a custom countdown time manually (1 minute to 48 hours)
- AUTO: Enter Auto Learn Mode - "teach" the timer a specific duration by running a task once
- BRGT: Adjust display brightness (levels 1-7)
Use Menu Button (Short Press) to cycle through options. Use Start/Stop Button (Long Press) to select an option.
This feature allows you to "teach" the timer a specific duration by running a task once:
- Enter Menu (Long Press Menu) → Select "AUTO" (Long Press Start/Stop)
- The display will show "rEdY" (Ready)
- Start Learning: Long Press Start/Stop to begin
- The Relay turns ON
- The timer counts UP
- Finish Learning: Short Press Start/Stop when your task is done
- The Timer stops and Relay turns OFF
- The duration is automatically rounded to the nearest minute and saved
- Display shows "SAVE"
- The device returns to Idle with the new learned time set
| State | Button | Action | Function |
|---|---|---|---|
| Idle | M | Long Press | Enter Menu |
| Idle | S | Long Press | START TIMER |
| Running | S | Short Press | STOP Timer |
| Running | S | Long Press | PAUSE Timer |
| Paused | S | Long Press | RESUME Timer |
| Menu | M | Short Press | Next Option |
| Menu | S | Short Press | Exit Menu |
| Menu | S | Long Press | Select Option |
| Setting | S | Short Press | Increase / Next |
| Setting | M | Short Press | Decrease |
| Setting | S | Long Press | SAVE SETTINGS |
To save power, the display will automatically dim or turn off after a period of inactivity (default 5 minutes).
- Wake Up: Press ANY button to wake the device. The first press only wakes the device and does not trigger an action.
For detailed operation instructions, see the Product Manual.
⚠️ IMPORTANT SAFETY INFORMATION
- ✅ Do not exceed relay current or power ratings (10A / 2500 VA)
- ✅ Suitable for inductive loads due to snubber protection
- ✅ Install inside a proper electrical enclosure
- ✅ Always test wiring with a dummy load first
- ✅ Ensure proper grounding of the electrical system
- ❌ Do not expose to moisture, dust, or excessive heat
- ❌ Do not operate in explosive or hazardous environments
- ❌ Do not modify or disassemble the device
- ❌ Do not use with loads exceeding rated specifications
- ❌ Do not install without proper electrical protection (MCB/RCB)
- Keep the device clean and free from dust
- Periodically check terminal connections for tightness
- Inspect for any signs of damage or overheating
- Replace if any physical damage is observed
- Settings are saved to internal Flash memory: All timer settings and configurations are stored in non-volatile Flash memory
- Avoid excessive unnecessary saving operations: To prolong memory life, only save settings when you need to change them. The device automatically saves when you complete a configuration change
- Power Failure Memory: Settings are retained even after power loss
- Relay Load: Ensure the connected appliance does not exceed the relay's rated current (typically 10A/250VAC, check relay casing)
- Data Saving: Settings are saved to internal Flash memory. Avoid excessive unnecessary saving operations to prolong memory life
- Safety: Do not touch the board while powered if high voltage is connected to the relay
This project is licensed under the CERN Open Hardware Licence Version 2 - Strongly Reciprocal (CERN-OHL-S v2).
⚠️ Commercial manufacturing, resale, or distribution requires permission.
You may redistribute and modify this documentation and make products using it under the terms of the CERN-OHL-S v2. This source is distributed WITHOUT ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING OF MERCHANTABILITY, SATISFACTORY QUALITY, AND FITNESS FOR A PARTICULAR PURPOSE.
- See the LICENSE file for details
- Visit CERN Open Hardware Licence for the full license text
| Contact Method | Details |
|---|---|
| rk@saiinnovation.com | |
| Website | emptyidea.in |
For technical support, warranty claims, or access to the latest source code, please contact us via email.
- Product Manual - Complete user manual with wiring diagrams, specifications, and operation instructions
This is an open-source hardware project. Contributions, improvements, and feedback are welcome. However, please note that commercial use requires permission from the copyright holders.
- Designed and developed by: EmptyIdea / Sai Innovation
- Licensed under: CERN-OHL-S v2
Model: EIMPTLA10A - Multipurpose Timer Lite-A
Version: 2.1
Last Updated: 2025
Professional AC Appliance Control Solution