What it shows
The strength of a radio signal, measured as RSSI in dBm, falls with distance and with obstacles like walls. Measuring it at grid points shows dead spots and where a router should be placed.
The science
The received power of a radio wave falls roughly with the square of the distance, and walls, people and metal absorb and reflect it. RSSI is reported in dBm: 0 dBm is 1 milliwatt, and each step of minus 3 dBm halves the power. Typical values are minus 40 dBm very close to the router, minus 70 dBm for a weak connection and minus 90 dBm for hardly any. Averaging many readings smooths out the fluctuations caused by reflections.
Materials
Cost: under Rs 1,500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An ESP32 development board
- A power bank and USB cable
- A 0.96 inch OLED display (optional)
- A tape measure and chalk or masking tape
- Squared paper or a spreadsheet
- Your own home or school Wi-Fi router (with permission)
Safety
For this project: USB power only. Only measure your own network or one you have permission to use. Do not try to connect to other people’s Wi-Fi.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Mark a grid on the floor of the room using tape, with points every 1 metre.
Write a sketch that calls WiFi.scanNetworks() and finds the entry for your router’s name, printing its RSSI.
Take ten scans at each grid point, hold the ESP32 at a fixed height and average the values.
Write each average in the matching cell of a grid on squared paper.
Colour each cell from green (strong) through yellow to red (weak) to make the heat map.
Find the weakest spot and move your body or a metal object to see the effect.
Move the router 2 metres and measure again; compare the two maps.
Plot RSSI against distance in a straight line and see if it follows the expected curve.
What you should see
The heat map shows strong signal near the router and weak patches behind walls and large metal objects, and moving the router changes the map.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What does RSSI measure?
The strength of the received radio signal, in dBm.
2What does a drop of 3 dBm mean?
The power falls to half.
3Why average several scans?
The signal fluctuates because of reflections, so one scan is not reliable.
4What materials block Wi-Fi most?
Metal, water (including people) and thick concrete walls.
Take it further
Add a distance-travelled estimate with an MPU6050 and walk the ESP32 around to draw the map automatically.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Hardware & repair
Computer Networking Study Book
The complete study notes, practice questions and glossary for Computer Networking