A Kindernet - digital telecomms exercise using children in lieu of electronics.

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A Kindernet

A simple, low-cost, 45 minute, fun participation exercise for a group of children aged 9 to 16 (or older) which teaches them how digital images are transmitted from one device to another remote device e.g. mobile phones.  It covers all the essential stages and principles involved: digital image rendering, digital encoding, data transmission using pulsed light, data decoding, image re‑creation, and includes error correction, re-transmission, and the use of predictive decoding to improve speed and accuracy.  Optionally, redundancy.

Here’s what you need:

  • A minimum of five children aged nine or more with reasonable mental and dexterity skills for the exercise, plus audience children.

  • Two rooms adjacent to a shared corridor or hall.

  • A desk/table in each room.

  • Two or more small LED torches with on-off switches which can be used to flash the light i.e. will not latch on if pressed gently – like an Aldis lamp.

  • Black, red, and blue broad-tip felt pens.

  • Two A4 sheets of paper with a large 5 x 5 grid, with the columns and rows numbered 1 – 5 (Excel is ideal).The sheets should also include clear instructions about how to use them: colour codes, order of colour, column, and row number flash elements etc. Colour codes are Red = 1, Blue = 2, Black = 3.

  • Spares of all the above.

Here’s what you do:

Pre-prepare a digital image by filling in the appropriate pixels on a grid sheet: a smiley face works well: pixels 2,1 and 4,1 (column, row) in blue for the eyes, pixel 3,3 in black for the nose, and pixels 1,4  2,5  3,5  4,5  and 5,4 in red for the mouth.

Select three groups of volunteer children (get teacher to do this): two groups of two to be Sender, and Receiver, and at least one to be the Internet and/or mobile phone mast.

The Sender pair consists of a Coder child, and a Sender child (who has a torch) sitting in one room. The Receiver pair consists of a Receiver child (who has a torch), and a Decoder child, who sit in the other room.  The fifth child also has a torch, and stands in the corridor in a position where s/he can see and be seen by both pairs.  If this is not possible, use two children as the internet/masts, relaying the flashes on.

Spend a few minutes making sure all the children - including the audience - understand the process, especially that the Coder and Decoder understand the X and Y pixel co‑ordinates system, and the torch-users should practice sending groups of three number flashes consistently and clearly with appropriate pauses between each number.  Make sure the torch users do not point the torches directly at eyes.

Tell the Decoder child that if s/he realises what the image is before all the data has been sent, to tell the Receiver to flash a “Finished” signal – one continuous three‑second flash back to the Sender, and then complete the image.

Now begin the exercise: the Coder examines the prepared image and determines the colour, column number, and row number of each non-blank pixel in turn, telling the Sender the three numbers: e.g. “Two, Four, One” for the blue left eye at 4,1.  The Sender then flashes the three numbers of the first pixel at the Internet/Mast, who in turn relays the flashes to the Receiver, who then tells the Decoder the three numbers.  The Decoder then fills in the appropriate pixel in the correct colour.  Then the Senders process the next pixel and so on until the image is complete, which is signalled by one long flash of six seconds.

During the exercise, errors will naturally occur:  the Ambassador should monitor the accuracy of each transmission with help from another adult if needed, and when an error is made, the Ambassador should stop the Decoder filling in a wrong pixel, and tell the Receiver to flash an “Error” code – six flashes – back through the network to the Sender, who then re-sends the numbers.  When this happens, explain that all this also happens in a real network.  When – inevitably – the Decoder is able to complete the image before all data has been sent, explain that real systems also do this using prediction algorithms and stored library images.

Audience children not in the teams should circulate between the Sender room and Receiver room to see what they are doing (needs management by teacher for young children).  When finished, all children should assemble in one room, and the STEM Ambassador should hold up the sent and received images: hopefully the same!

Finally, explain to the children how what each child did replicates the actual process of sending a real image from one phone to another, and how the differences between the exercise and real life are only ones of scale: image resolution, pixel colours and luminance, coding and error-correction complexity, and transmission speed.  Explain how the same process can transmit sound, streaming video and other baseband data where only the transponders at each end are different.


  • You can shorten and simplify by using a black and white only and/or fewer-pixels image: choose one which is very familiar even when only partly complete.

  • The pixels can be sent in any order, and more than once, demonstrating redundancy, perhaps instead of re-transmission.

  • Rather than just producing the prepared image, put it in a dummy “camera” made from a breakfast cereal box painted black with a small transparent food container bottom as a “lens”: at the beginning of the exercise, tell the children you are going to secretly photograph something to create the image, leave the room with a volunteer child to “help”, then return and remove the image – unrevealed – from the camera, and pass it discreetly to the Encoder.  At the end, claim the image was a photo of the “helper” child’s face, albeit very low-res.

  • Could be elaborated for older children or adults by increasing image resolution, more colours, variable luminance.

  • To illustrate fibre optics in the Internet, use a length of glass fibre strand and torch, or clear plastic pipe filled with water, for one leg of the network.

  • Can be done in one room, but need to position things and people so the Receivers can’t see the image.

  • One leg of the “Internet” could be as long as the torch is visible.

  • Instead of torches, could use fingers held up, but palm outwards, so the number two is a Churchillian Victory sign, not the other two-finger sign!

Nick Davies

STEM Ambassador

20 March 2018

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