Tangible design interaction study
Food Charm
Share food, build a community with food.
Context
University Project
Team
5 Designers
Supervised by
Wendy E. Mackay
Timeline
Nov - Dec 2025
Overview
A community keychain plus shared food lockers for giving away surplus food and finding food nearby. Concept and video prototype; not built.
Students who can’t afford food, students who overbuy, and nearby restaurants with unsold food.
Designer in Group 2. Co-authored every worksheet shown here; ran my own story interviews (2 rounds × 2 participants).
This project explores how tangible interactions can make food sharing more accessible, immediate and socially comfortable. Through a community-based keychain and shared food lockers, the concept connects people with surplus food to people who need it, while reducing unnecessary food waste.
How we worked
Three phases, one shared set of worksheets
Wendy E. Mackay’s DO IT method: every artefact built as a group, critiqued, then fed into the next.
01
Discover users
Story interviews: how people actually handled food they couldn’t finish
User profile: who the system is for
Breakdown analysis: breakdowns and workarounds in today’s food habits
Current scenario: a realistic evening that exposes the gaps
12 to 13 Nov 2025
02
Design prototypes
Design concept: audience, behaviour, core idea
Design alternatives: three combinations, compared
Radar diagram: keychain vs fridge on six dimensions
Future scenario & storyboard: the concept acted out frame by frame
Object & operations tables: objects, commands, feedback, responses
18 to 25 Nov 2025
03
Evaluate systems
Design experiment: single screen vs covered screen
Walkthrough review: where the flow breaks
Improvements & redesign: fixes, then a simpler system
Revised storyboard & video: the keychain-and-locker version
2 to 9 Dec 2025
The problem
Edible food is thrown away a few doors from someone skipping meals
Both sides often live in the same residence. What separates them is effort, timing and awkwardness.
Too much
Food that won’t get eaten
Students who buy more than they can eat, often on promotions, then run out of time to cook.
Restaurants and supermarkets with edible food left at closing time.
Givers feel guilty throwing it away.
What gets in the way
Posting, replying and arranging a handover takes more time than binning it.
Food spoils before anyone replies; restaurants can’t wait around after closing.
Pickup is too far, unclear, or depends on meeting a stranger.
Vegan, vegetarian, halal: a free offer is useless if you can’t eat it.
Asking for free food feels embarrassing, so people skip meals instead.
Not enough
Food people can’t afford
Students without enough family or scholarship support struggle to afford groceries.
Prepared food is out of reach even after a long, tiring day.
Affordable stores can be far from campus.
So, how might we make giving and receiving nearby food fast, low-effort and comfortable for both sides?
Research
Story interviews
Two rounds, two participants each, about one specific recent moment. I redid round 1 to meet the brief.
Research insights
Breakdowns and workarounds
Coded as a group from interviews and scenarios.
12 Nov 2025
Breakdown
Users can’t easily find food that matches their dietary preferences (vegan, gluten-free, halal).
Breakdown
Users don’t get notified when nearby stores have surplus food at times that fit their schedule.
Breakdown
With very little money, prepared food from restaurants is out of reach, even when exhausted.
Workaround
Leftovers were about to be thrown away; the user gave them to neighbours instead.
Workaround
Before leaving the country, a user cooked as many unused ingredients as possible and threw a farewell party.
Workaround
Users search for cheaper brands or quantities to stay within a tight budget.
Research
User personas
Richie
Giver
Financially stable student who always buys too much food and is waste-conscious.
Brooke
Receiver
Financially needy student who struggles all month to buy groceries; her parents don’t support her for food. She is our extreme character that will push us to think…
Luc
Restaurant owner
Runs an Italian restaurant near Brooke’s university and regularly gives leftovers to students who need them.
Scenarios
One evening in a student residence…
Current scenario: three neighbours, one evening.
Richie
Student with too many groceries
His fridge holds 3 kg of wilting spinach, 3 bottles of milk and 2 packs of chicken, all expiring in 3 days. Deadlines mean he won’t cook. A group-chat offer gets no replies, so he carries it to the bin.
Breakdown
No fast, trusted way to give leftovers away nearby.
Brooke
Student skipping meals
She has been rationing bread for weeks. She spots Richie at the bin and, embarrassed but desperate, asks if she can take the food. They joke about a “broke-student club”.
User innovation
Spontaneous, informal sharing between neighbours.
Luc
Restaurant owner
Next evening he posts “two portions of soup, 10 minutes” in the dorm WhatsApp. Three students reply at once, nobody knows who gets what, and he still has to wait. He wishes he could just drop the food somewhere safe.
Breakdown
Chaotic coordination; owners stuck waiting.
Opportunity: a system that allows fast, safe and embarrassment-free exchanges of surplus food between students and local businesses.
Future scenario
First storyboard: the smart fridge does the heavy lifting
Early concept. A smart fridge spots expiring food; the keychain only says yes/no and shows a map. Early concept, not final.
25 Nov 2025
01 Title card
02 Richie in his kitchen hears the fridge chime
03 Spinach expires in 1 day: Recipe or Give away
04 He confirms the item and uploads the offer
05 Brooke walks home from uni, hungry; her keychain sounds
06 She taps Yes to claim the food
07 Flips the keychain: the pickup point is a 4-min walk
08 Pickup point at the student residence
09 Luc types his leftover burgers on the fridge screen
10 “Offer successfully posted”
11 Brooke’s keychain shows Luc’s Burgers: Yes / No
12 She collects a burger at the counter
Scroll sideways for all 12 frames →
Final storyboard & user journey
Richie gives, Brooke collects, Luc says hello
No fridge: Richie posts at a locker, Brooke accepts with a flick, and the keychains introduce her to Luc.
9 Dec 2025
01 Richie turns the dial to zoom the map and find the nearest locker
02 At the lockers he scans the QR code; the screen assigns a locker
03 Brooke gets a nearby-food alert and flicks right to accept
04 She heads to the lockers a short walk from her residence
05 Near the lockers, two keychains vibrate
06 “New friend nearby. Common liking: Italian food”
07 Brooke and Luc notice each other’s keychains
08 They tap keychains: a chime confirms they’re food friends
Stage
1. Offer
Richie
2. Match
System → Brooke
3. Collect
Brooke
4. Connect
Brooke & Luc
Action
Spots spinach he won’t eat. At the community locker, photographs it with his keychain and confirms label, category and quantity.
Nothing. The offer goes to the closest active keychains first, within about a 10-minute walk.
Flicks right to accept, follows the map to the locker, scans the QR code.
Near the lockers, both keychains vibrate: they share a liking for Italian food. They tap keychains together.
Feedback
Keychain assigns a locker number and a QR code. A safe default best-before is set by category; he can adjust freshness with the dial.
Brooke’s keychain vibrates. She sees the food photo, category, quantity and the pickup address together.
The locker opens. She can cancel the reservation at any time, or extend the time limit by 10 minutes.
A chime confirms they’re “food friends”; Brooke gets priority when Luc gives food away.
Watch-out
Typing on a tiny screen was a breakdown, so posting became photo + two choices.
If she rejects, the offer moves to the next closest person.
Rigid time limits and unloved pickup spots were walkthrough issues.
Still open: unwanted encounters from proximity, and FOMO about posts.
Design exploration
From a smart fridge to a keychain
Our first concept split the work between a smart fridge and a small keychain.
18 Nov 2025
Smart fridge (embedded)
A display on the fridge door with an expiry-date scanner and notification, suggests recipes, and lets you post an offer, all connected to the sharing community.
Keychain (worn)
Vibrates when surplus food is available within the wearer’s radius. The back of the keychain shows a map to the pickup point.
Three alternatives on two dimensions
Two dimensions, urgency and locating, combined into three alternatives.
Urgency
Keychain sound
Fridge alert: new surplus
Fridge alert: expiry
Locating
Restaurant poster
Text address
Map
Alternative 1
Keychain sound + restaurant poster
The keychain beeps when you enter a zone with surplus food; the fridge later shows poster-like summaries.
Better: Low cognitive load, ambient awareness, light to carry.
Worse: No specific info; you only see details at home, so it’s slow and you can miss food.
Alternative 2
Fridge alert (new surplus) + text address
The fridge chimes when a new offer appears and shows its address as text.
Better: Precise, actionable, immediate.
Worse: Addresses take effort to interpret; only helps takers, not givers with expiring food.
Alternative 3
Fridge alert (expiry) + map
The fridge flags near-expiry food and suggests sharing it; takers navigate with a map.
Better: Supports urgent action; fastest navigation; best at preventing waste.
Worse: More complex interaction and needs a large display across devices.
What we kept
Keychain for low- and medium-urgency alerts (1 + 2), fridge for expiry alerts (3), map for takers (3). Still two devices; the redesign later removed the fridge.
20 Nov 2025
Other questions we argued about
?
Giver-centred or receiver-centred?
?
Typing, scanning or AI recognition for food input?
?
Embedded in a fridge or worn as a keychain?
?
System-triggered or user-triggered?
?
Keychain or app? Debated in our workshop
?
Central pickup points or peer-to-peer? Debated in our workshop
Comparing the devices
Keychain vs fridge, on six dimensions
Qualitative: each tick is a category from our discussion, not a score. Toggle a device to compare.
What it showed us
Keychain: system-triggered, urgent, map-based, minimal input.
Fridge: the giver-centric work of detecting, displaying and typing.
Once posting moved to the keychain and storage to lockers, the fridge had no job left.
Original sketch, click to zoom.
Participatory design
We ran a participatory design workshop
In Wendy Mackay’s DOIT method, a participatory design workshop brings users into the design process. The team moderates, records and debriefs, while participants generate and critique ideas with the prototype in hand. We used it to test our two biggest open questions with other students.
Activity 1
Customise your own keychain
Personalise your Food Charm and build a micro-community through keychain connections.
1
Pick a paper keychain.
2
Draw your preferences on its screen: colours, design, food preferences (vegan, spicy food, desserts).
3
Meet another keychain holder. Compare how you get groceries and what you do when food goes bad.
4
Would you share food with this person?
Activity 2
Debate on design
Debate two proposed design alternatives in teams of four.
1
Debate both topics within your team: Keychain vs App (8 min), then Centralised pickup points vs Peer-to-peer exchanges (8 min).
2
Form two mixed groups, with members from both teams, and compare your conclusions.
Tangible interaction
The keychain is the interface
Small and always with you, so every input is something your hand does.
01 Connect with friends
Proximity-based notification when someone nearby shares your food preferences. Hold keychains together to add each other.
02 Rotate the outer rim
Adjust the map view, or select the freshness level of the food you’re donating.
03 Turn left & right
Left for back or reject. Right for next or accept.
04 Go to food lockers
Nearest lockers to grab or give food. A QR code secures each locker; a built-in camera shows the food’s current status.
Mockups
Clips on to whatever you carry
The idea is to eliminate any frcition of use to the user. IT should be easy to carry anywhere.
On a backpack
On a belt loop
Defining the interaction
Objects, operations and feedback
For each object, its operations; for each operation, the command, feedback and system response.
Our object and operations tables (click to zoom). They predate the redesign, so the fridge’s food list and recipes still appear.
Accept food
Command: Press the accept button
Feedback: Keychain vibrates
Response: Map to the pickup point appears
Start journey
Command: Long-press the map
Feedback: Arrow points in the moving direction
Response: Detects the user’s movement
View food image
Command: Tap “view food image”
Feedback: The image appears
Response: Food image is shown
Design experiment
One screen, or a screen under a cover?
Snippet: a nearby-food alert arrives; accept or decline, then find the location.
2 Dec 2025
A
Single screen
Notification, accept/decline and map all on one exposed screen. Nothing to open.
Trade-off for: Fastest and simplest; act immediately, with less effort.
Trade-off against: Easier to scratch; can feel overwhelming if too much shows at once.
B
Covered screen
Like a hunter-case pocket watch: an LED text display and accept/decline buttons on the cover, the detailed screen and map inside.
Trade-off for: Clear split between quick actions and details; protects the screen; more physical and intentional.
Trade-off against: Opening the cover is an extra step for the map; the hinge may wear or feel slow in a hurry.
This is what we chose ↓
Null hypothesis
There will be no significant difference in user performance between the single-screen design and the covered-screen design.
Independent variables
Input type: physical buttons vs touch
Number of screens: one vs two
Notification type: vibration vs LED
Familiarity with food sharing
Dependent variables (what we’d measure)
01
Error rate
02
Cognitive load
03
Number of interaction steps
04
Task completion time
05
User satisfaction
06
Perceived trust or confidence
07
Physical effort or comfort
08
Notification response time
09
How often extra info is opened
10
Interaction-flow interruptions
Iterations & improvements
What the walkthrough broke, and what we changed
We stepped through the flow and logged where it broke.
2 Dec 2025
You may not go, and the giver never knows
→
Cancel the reservation at any time
You miss food you wanted
→
Reserve more offers at the same pickup point
The system isn’t updated when food is taken
→
Validation with a QR code
Food a little farther away becomes unreachable
→
Extend the time limit by 10 minutes
Confusion over who collects what
→
Each offer gets its own locker and QR code (from the redesign)
You accept, then dislike the pickup point
→
Show the food and the address together
Then, a broader redesign
Simpler technology, lower cost: no more smart fridge
Rebuilt around a portable keychain and community lockers. Food is collected quickly, so most lockers need no refrigeration.
Post. Take a photo with the keychain, confirm label, category and quantity.
Match. The closest active keychain is notified first, within about 10 minutes’ walk (editable up to 20). If they decline, it moves on.
Collect. Reach the locker within 20 minutes or the reservation is released to someone else.
Compost. Once the best-before passes, composting organisations are notified for food that’s safe to compost.
Safe default best-before
Fresh produce
2 days
Dairy and eggs
1 week
Dry goods / packaged
1 month
Cooked meals
2 to 3 hours
Addressed by the final concept
✓ Expanding the search area on the map (dial zoom)
✓ A screen too small to type on, and a fridge that was overkill
✓ Freshness as an adjustable parameter
Still open
○ Food can look perfect in a post but still be bad or expired
○ Unwanted encounters caused by proximity connect
○ FOMO about posts: anxiety and competition
Final concept · video prototype
Video walkthrough of the final concept
Our video prototype: paper keychains, a real kitchen and a cabinet standing in for the lockers. Richie posts, Brooke collects, and the keychains introduce her to Luc.
9 Dec 2025
What I learned
Designing an object, not just a screen
01
The physical interaction matters as much as the information
Deciding that a flick means accept shaped the device more than any screen layout did.
02
Urgency and hierarchy decide how fast people can act
Our alternatives traded ambient beeps against precise addresses. What you show first changes what people do next.
03
Physical controls give a small device purpose, but every step costs
The covered screen is more intentional and protects the display, but it adds a step before the map.
04
Where and when you collect is part of the interaction
Pickup spots, time limits and reservations caused most of our walkthrough issues. They aren’t just logistics.
05
Stigma and trust are design problems
A peer gesture, a locker instead of a handover, and validation by QR code all aim at comfort, not just communication.
06
Iteration can mean taking technology away
The concept got clearer when we removed the smart fridge, not when we added features.
The team
Taught by Wendy E. Mackay
Every method on this page, from story interviews and breakdown analysis to storyboards, walkthroughs and video prototyping, comes from the DOIT (Design of Interactive Things) course taught by Wendy E. Mackay, on the left in the photo.
Explore the DOIT design guidelines
Wendy is a Research Director at Inria and leads the ExSitu human-computer interaction group at Université Paris-Saclay.
From building the first interactive video system at Digital Equipment and her work at Xerox EuroPARC, she has helped shape participatory design, video prototyping, interactive paper and tangible computing. She chaired CHI 2013 and received the ACM SIGCHI Lifetime Achievement Service Award.
Food Charm was designed for University project. It’s a concept with storyboards and a paper video prototype. It was not built nor deployed.
Fun fact!
Shared food points already exist in Europe. In Germany, foodsharing.de runs public “Fairteiler” shelves and fridges where anyone can drop off or pick up food; its volunteer network has saved over 100 million kilograms of food. In Stockholm, Karma and Electrolux trialled a smart fridge you unlock with a QR code. Food Charm builds on the same idea and adds the missing piece: a keychain that tells you when there’s food nearby.
Visit foodsharing.de ↗