Physics · Electronics
Build a crystal radio receiver
Receive AM radio with no battery using a coil, a diode and a long wire aerial.
- DifficultyAdvanced
- Estimated time1–2 weeks
- Budget₹250–₹500
- ClassClass 11 to college
- TeamSolo or up to 2
- You needBasic electronics
Prerequisites: None beyond your class work
Original · by TechnifyedHardware ProjectWorking ModelLow costHardware
Overview
Receive AM radio with no battery using a coil, a diode and a long wire aerial.
Skills you will use
Safety
- Hot surfaces and liquids can burn. Use tongs or oven gloves and let things cool before touching them.
Materials and tools
- Enamelled wire
- Card tube
- Germanium diode (1N34A)
- Variable capacitor or sliding contact
- High-impedance earphone
- 15 m aerial wire
- Earth connection
Tools and software
Step-by-step roadmap
Start
You will finish with: a working receiver and an explanation of tuning and detection.
- 1
Prerequisites
Nothing special to know first. Then collect the 7 items in the materials list.
- 2
Learn
Read up on electronics: diode detector, radio waves, resonance. Your textbook chapter and one short video are enough.
- 3
Plan
Sketch the design, list every part with its price and decide how you will know it works.
- 4
Build
- Wind about 80 turns on the tube and bare a strip for a sliding contact.
- Connect the aerial to one end and earth to the other.
- Connect the diode and earphone across the tuned part.
- Slide the contact slowly until a station is heard.
- Record which coil positions give which stations.
- 5
Test
Run it ten times in a row. Note every failure, fix the cause and test again.
- 6
Document
Photograph each build stage, keep the circuit or drawing, and note what failed and how you fixed it. Report structure
- 7
Present
Demonstrate it working first, then explain how it works and what you would improve. Presentation structure
- 8
Publish
Share a short video, the parts list and the drawing or code so someone else can build it.
Expected outcome
A working receiver and an explanation of tuning and detection.
Other versions of this project
Advanced version
Calculate the resonant frequency for each coil setting and compare with station frequencies.
Ways to do this project
Text marked "You write this" is a prompt for your own work; everything else is specific to this project.
- Problem
- You write thisWrite your question as: How does [what you change] affect [what you measure]?
- Hypothesis
- You write thisWrite it as: If [I change this], then [this will happen], because [reason].
- Variables
- You write thisName the one thing you change (independent), the thing you measure (dependent) and what you keep the same (controlled).
Materials and procedure are in Materials and the Roadmap.
Observation table
You write thisDraw a table with one column for what you change, one for each repeat reading and one for the average.
- Graph
- You write thisPlot what you changed along the bottom and what you measured up the side; use a bar chart for categories and a line graph for numbers.
- Results
- You write thisState what the graph shows in one or two sentences, with numbers.
- Conclusion
- You write thisSay whether the result supports your hypothesis and why you think so.
Display board
- Title and your name
- Question
- Hypothesis
- Materials
- Procedure (with photos)
- Data table and graph
- Conclusion
- What you would do next
Questions judges ask
- What would you change if you did this again?
- What was your biggest source of error, and how did you reduce it?
- Where is this idea used in real life?
- Research question
- You write thisOne question you can answer with data, narrow enough to finish in the time you have.
- Hypothesis
- You write thisWhat you expect to find, and why.
- Variables
- You write thisWhat you change or compare, what you measure, and what you hold constant.
- Methodology
- You write thisDescribe the method in enough detail that someone else could repeat it: sample, tools, procedure.
- Data collection
- You write thisSay what you will record, how many times, and how you will keep the records safe.
- Analysis
- You write thisChoose the table, chart or test that answers the question; report averages with their spread.
- Limitations
- You write thisList what could have affected the result: small sample, instrument limits, things you could not control.
Literature review
Find five to eight sources (your textbook, review articles, reports) and note what each says about your question. Group them by idea, not one after another, and end with what is still not known.
References
List every source you used in one style throughout (author, year, title, where it was published, link and the date you opened it).
Working as a team
Solo or up to 2. Suggested roles:
Report and presentation
Report structure
- Title and aim
- The problem it solves
- How it works (principle)
- Parts list with cost
- Design: drawing, circuit or block diagram
- Build steps
- Testing and results
- Problems faced and fixes
- Limitations
- Future improvements
- References
Presentation structure
- The problem
- The idea
- How it works (one diagram)
- Parts and cost
- The build (photos)
- Live demo or video
- Test results
- What did not work
- Next version
Viva questions
Prepare your own answers to these before you present.
- What is the aim of your project, in one sentence?
- What is the principle behind it?
- Why did you choose these materials or tools?
- What result did you get, and was it what you expected?
- What went wrong and how did you fix it?
- How could this be improved or used in real life?
Resources
Source and attribution
Original
Written by Technifyed. Free to use for your own school or college project; write the report in your own words. Added 1 Oct 2026.
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