MECHATRONICS / SMART HOME

Power Saving Smart Door Lock System

A differential door-lock design that uses outside locking to trigger shutdown of nonessential household loads.

Student survey responses: 30
Compared design concepts: 3
Selected concept’s weighted score: 3.15

Concept illustration linking a door lock to household lighting and electrical loads — Concept illustration of the power saving door-lock idea. The supplied resources document the design study rather than the illustrated hardware.

Design brief & team

Group 17 developed the Home Power Saving Door Lock System for ME 3201: Engineering Design Methodology at the University of Ruhuna’s Department of Mechanical and Manufacturing Engineering.

The aim was to reduce electricity wasted by appliances left on when everyone leaves home. The design links a door-lock action to the power saving system so that nonessential loads can be switched off automatically.

The presentation lists N. A. A. Dhananjaya (EG/2021/4476), W. S. R. K. Perera (EG/2021/4717), H. S. D. Rodrigo (EG/2021/4763) and R. P. J. Rukshan (EG/2021/4766). It documents a group design effort without allocating individual subsystem responsibilities.

Design presentation · PDF page 1

User research

The team surveyed university students about electricity costs, forgetting powered devices when leaving home, and interest in an automatic solution. Each displayed chart records 30 responses.

The largest electricity-bill group, 43.3%, selected Rs. 1,000–5,000 per month; 33.3% selected Rs. 5,000–10,000. On the question about leaving devices powered, 26 of 30 respondents gave a nonzero rating on the 0–5 scale. All 30 expressed interest in the proposed door-lock addition.

These responses informed the design brief. They describe this student sample’s preferences and habits, rather than measured savings from the system.

Survey chart showing ratings for leaving devices powered, with 30 responses — Student survey · ratings 0–5: 4, 12, 8, 4, 2 and 0 responses respectively. Source: slide 6.

Survey pie chart showing all 30 respondents interested in the proposed automatic shutoff feature — All 30 respondents expressed interest in the proposed feature. Source: slide 7.

Design presentation · PDF page 5 Design presentation · PDF page 6 Design presentation · PDF page 7

Objectives & functional analysis

The objective tree groups requirements around power and energy saving, safety and durability. It calls for interrupting loads that do not need continuous power while maintaining supply to refrigerators, CCTV, security alarms and other equipment that must remain active.

The functional analysis separates user-state recognition, identification of essential and nonessential loads, activation and deactivation from door-lock events, and a user-accessible manual override. These are design requirements; the presentation does not provide an installed switching circuit or test record.

Objective tree from the design presentation covering power saving, safety and durability — Objective tree · source: slide 9.

Functional analysis linking user recognition, load identification, system activation and manual override — Functional analysis · source: slide 10.

Design presentation · PDF page 9 Design presentation · PDF page 10

Concept generation

A morphological analysis compared alternatives for the deadbolt arrangement, handle, differential locking mechanism, body material and outside-lock recognition. Options included a shared deadbolt or separate deadbolts, key or adjustable hand-latch operation, stainless steel/brass/copper bodies, and a switch, sensor or deadbolt-completed circuit for recognition.

The team combined these alternatives into three candidate designs before comparing their weighted scores.

Morphological analysis table comparing three alternatives for five door-lock functions — Original morphological analysis table. Source: slide 11; candidate combinations appear in the full PDF.

Design presentation · PDF page 11

Weighted concept selection

The decision matrix gave the greatest weights to protection by the lock (25%) and durability (20%). Ease of manufacture, low cost and user safety each received 15%; ease of handling received 10%.

Design 02 ranked first with a weighted score of 3.15, ahead of Design 01 at 2.60 and Design 03 at 2.45. The presentation selects Design 02 for further development.

The candidate combination shown for Design 02 is A3B3C2D3E1: separate deadbolts, a metal handle with a rubber grip, an outside key with an inside adjustable hand latch, a copper body, and switch recognition. These are the documented concept selections.

Weighted decision matrix ranking Design 02 first at 3.15, Design 01 second at 2.6 and Design 03 third at 2.45 — Original weighted decision matrix · concept comparison scores, not measured operating performance. Source: slide 12.

Design presentation · PDF page 11 Design presentation · PDF page 12

Differential locking principle

The proposed lock distinguishes locking from inside and outside through separate deadbolts. Locking from outside sends a signal to the power saving system to indicate that the household has left; the system can then disconnect the nonessential loads while preserving essential supply.

This approach uses the locking action as a proxy for occupancy. Its operating assumption is that outside locking means everyone has left. It does not independently count occupants or verify that the house is empty.

Design presentation · PDF page 14

Design outcome & available evidence

The study presents a survey-informed brief, functional requirements, three candidate concepts and a documented selection of a differential lock. The anticipated benefit is reduced waste from forgotten electrical loads.

The supplied PDF and PowerPoint contain the same 16-slide presentation. They do not include a detailed CAD assembly, fabricated prototype photographs, a switching schematic, or measured energy savings. The cover remains a labelled concept illustration; the original analysis figures and both source files are provided below.

Design presentation · PDF page 15 Design presentation · PDF page 16