💎 Radio Treasure Hunt

What is a radio treasure hunt?

It is hide-and-seek, except the thing you hide gives itself away by radio instead of by being visible. One small computer — the Treasure — is hidden somewhere and quietly transmits. Everyone else carries a Hound, which cannot see the Treasure and cannot point at it, but can tell how strong the signal is. Players work out where the Treasure must be by moving around and watching that strength change.

Real radio amateurs do this as a sport, on foot and over several kilometres; it is called amateur radio direction finding, and you will also see it called a “fox hunt”, after the hidden transmitter. This is a small version for a playground, a park or a school field.

The Treasure sends out three signals, not one

That is the trick that makes it playable. The Treasure transmits a loud signal, a medium one and a quiet one, over and over. The loud one carries a long way; the quiet one only reaches a few metres. So which of them a Hound can hear tells you roughly how close you are, and the Hound turns that into a beep rate.

Closer in, the display fills up and stops being useful — every bar lit looks the same at five metres as at one. Button A turns the Hound's sensitivity down a notch so the bars start responding again, which is how players close the last few metres.

What you need

• Two or more BBC micro:bit V2 boards. A micro:bit is a small programmable computer, about the size of a credit card, widely used in UK schools. V2 only — the game needs the speaker that the older V1 does not have. Two quick ways to tell them apart: on a V2 the micro:bit logo on the front is gold (it is a touch button), where a V1's is yellow and does nothing; and a V2's gold edge connector along the bottom has notches cut into it. The back of a V2 is also labelled MICROPHONE and SPEAKER, with the version printed in the bottom right corner. How to identify your micro:bit.
• A battery pack for each, usually 2×AAA. The Treasure has to run unattended for the whole session.
• A USB data cable to set the boards up from this page. Charge-only cables will not work — a very common stumbling block.
• Somewhere to play — ideally outdoors, 20–30 m across. A hall or a hut works for a quick game, but indoors the readings jump about because the signal bounces off the walls and floor. Outdoors is where the hunt works best.

How a game goes

1. Set the boards up from this page — one Treasure, as many Hounds as you have.
2. Hide the Treasure with its battery. It keeps its display switched off so it cannot be spotted.
3. Players sweep the area listening to their Hound. Slow beep means far, fast alarm means close.
4. There is no arrow to follow. The micro:bit's aerial is omnidirectional — it hears equally well from every direction — so the Hound can report strength but never bearing. Players get a direction from their own bodies instead: a person absorbs this kind of radio wave, so turning slowly on the spot until the reading dips puts the Treasure behind them. (Directional aerials do exist, and competitors in real events carry one that points straight at the transmitter. A micro:bit has the all-round kind built in.)
5. The first to find it wins. Ten to twenty minutes is typical for a school field.

First, each board needs the game copied onto it. The three steps below do that over USB — nothing to install, no account, and no programming required. Once a board is set up it needs only its battery. Allow about half a minute for the first board and a few seconds for each one after that, so a class set takes a few minutes. You need one Treasure, and one Hound per group of children.

Running this with a group? There is a teacher's lesson plan, a full investigation worksheet for a 90-minute science lesson, and a one-page 20-minute hunt card if you just want to play.

1. Choose a radio group

Most people should leave this alone. Change it only if another hunt might be running nearby at the same time — a second class, or another group in the same park.

The group is how the boards find each other. Every board in one game must be on the same one. If two boards differ, the Hound simply never hears anything and there is no error to see, so write the number on a sticker and put it on every board you set up.

The Treasure will also tell you. Press either button on it and it shows its group number on the LEDs for a second, then goes dark again — so a board whose sticker has come off can still be asked, out in the field, with no computer. The Hounds have no such button: theirs are the attenuator.

Running two hunts side by side? Give each one its own group so they do not chase each other's Treasure. Pick a group, set up that hunt's Treasure and Hounds, then change the number and do the next hunt. The running total below keeps each group separate.

Radio group

2. Connect a board

Plug one micro:bit in with a USB cable that carries data — a charge-only cable is the commonest reason nothing appears. Connect one board at a time.

Connect a micro:bit

3. Set it up

Set up as Treasure Set up as Hound Check the Treasure is working…

Check the Treasure is working

This turns the connected board into a listener so you can see what the Treasure is transmitting — useful before a session, or if a hunt is not working. It replaces the game on this board while it runs; put it back with the button below when you have finished. Leave the Treasure switched on somewhere nearby.

Put the game back (Hound) Stop watching

Boards you have set up

Sheets to print

Whether this is a science lesson or a Wednesday evening activity, there is a sheet for the players and a plan for whoever is running it. All three are written to be printed, and each has a print button at the top.

20-minute hunt card Full worksheet Plan for the leader

The hunt card is one side of A4 for a 20-minute game where the goal is simply to find the Treasure — the one to use for a club, a party, or a first go. The full worksheet is a 90-minute investigation with measurements and graphs, using this project's own field measurements. The plan is written for a Year 5–6 science lesson and is mapped to the national curriculum, but its 20-minute running order and its safety and kit notes work just as well for a pack or a troop.

Running a hunt

No Chrome? Download a .hex

These work in any browser: download, then drag the file onto the MICROBIT drive that appears when you plug the board in. micro:bit V2 only — on a V1 the board will simply not run, with nothing on screen to say why.

Download Treasure .hex Download Hound .hex