Radio science fair project for 4th grader?

[John_ITIC]

It is time again for science fair and my son has become old enough to show an interest in electronics! This year, he wanted to do something related to Radio. Can anyone recommend a very small kit that he can build himself and that is actually easy enough to understand for a 9 year old (with a good chunk of help from his EE Dad, of course)?

Essentially, this: http://www.education.com/science-fair/article/build-basic-radio/

[rdl]

Elenco has a variety of pretty good educational radio kits. They have good manuals that not only tell you how to build it, but also explain how it works.

http://www.elenco.com/product/productlist/radio_kits=MTc=

[sycho123321]

Hi, it is awesome that your son is getting interested in electronics! 
Here is a very simple 2 transistor 40m cw (morse code) transciver that you can buy as a kit. http://www.al7fs.us/AL7FS2.html that is a link talking about the circuit, and here is the link to the kit http://www.halted.com/commerce/ccp13844-enhanced-pixie2e-qrp-cw-transceiver-kit-pixie2e-kit240.htm but you can also get very inexpensive chinese knockoff kits such as this one http://www.ebay.com/itm/like/321745589972?ul_noapp=true&chn=ps&lpid=82.
I bought one of the cheap knockoffs and it is essentially the same as the genuine one.
I hope this helps!
Lukas

[Ian.M]

One can go all the way from a simple crystal set to a transistorised TRF radio capable of driving a small speaker.  Way back in the 70's Ladybird Books Ltd published a book on building a radio from scratch targeting children old enough to use simple hand tools.

See: http://www.mds975.co.uk/Content/trfradios02.html
and http://www.amazon.com/Making-Transistor-Radio-G-C-Dobbs/dp/0721403247

The baseboard should be kiln dried white pine or similar.  Rule out the layout using a Biro, not a pencil as you don't want conductive leakage paths.  Saturating the baseboard with paraffin wax using a white candle and a hot air gun after marking it out and drilling the pilot holes but before fitting any of the screws improves reliability.   The cup washers must be brass or heavily brass plated, but the screws can be ordinary steel woodscrews as they aren't in contact with the actual component leads.

The parts used are rather retro, but can still be obtained from specialist dealers, or you could modify the design and re-bias it to use silicon transistors.  Use modern AA batteries in a holder.

I've still got mine on the shelf from all those years ago. I rebuilt it in my early teens with a Vernier reduction dial on the tuning cap, and a plug-in Denco coil to tune some of the shortwave bands.  I remounted the original AM ferrite rod on a coil base so I could also use it on the MW band.  Its got a pop-riveted aluminium angle frame screwed to the corners of the baseboard holding the aluminium front and side panels, and if you dont look inside, you wouldn't realise it was built Ladybird style!  However its not currently working - I suspect due to oxidisation of some of the component leads.

For the basic crystal set, you do need a good aerial and earth, but the final reflex TRF set is sensitive enough to get local stations without an external aerial.

[vk3yedotcom]

Ideally you'd want something that can be taken to school and demonstrated.  That rules out crystal sets (and other simple receivers) due to the need for an outdoor antenna.

A simple FM bug transmitter is fun and would appeal to kids who like bugging people, hearing themselves on the radio, broadcasting funny noises or playing DJ.

 http://www.talkingelectronics.com/projects/Spy%20Circuits/SpyCircuits-1.html has some ideas.

A 2 transistor FM bug can be extremely sensitive and have a good range.  Get extra points for putting the microphone on a long lead and the transmitter on a long pole above the roof.  Add a 3.5mm plug to allow audio from a computer etc to be broadcast.

A relay connected in a latching / buzzer circuit is a very simple spark transmitter that could be heard on an AM radio.

Another possibility, and one that doesn't involve soldering, is something with 433 MHz modules and solderless breadboard.

Super regenerative FM receivers are also fun and don't need an antenna.  They don't use many parts but can be tricky to get going.  Like a bug they can interfere with other's reception.  Maybe for an older age group? 

[John_ITIC]

Thanks everyone for your responses. I have looked at some of the links/videos and I think I will look into a "Wireless telegraph" design some more. I know the 4th grade kids learned about "wired" telegraph in school this year and it should be fairly simple to create a CW transmitter and receiver built with "nails on a board" and separated by a foot or two of space. This allows the kids to operate the telegraph key on one end and hear the beeps come out magically out of a speaker on the other side! Perhaps two separate boards can be built so they can be carried away as experimentation of transmitting over some distance.

The question now is: what is the absolutely simplest CW transmitter and receiver circuits? The frequency doesn't matter and the distance transmitted only needs to be about two feet. I can imagine the transmitter simply being an oscillator and a transistor for output power. The receiver will likely be a little more complex.

I suppose any form of crude "spark-gap" design is out since it has to work with a small battery and minimal parts.

Thanks!

[vk3yedotcom]

Thanks everyone for your responses. I have looked at some of the links/videos and I think I will look into a "Wireless telegraph" design some more. I know the 4th grade kids learned about "wired" telegraph in school this year and it should be fairly simple to create a CW transmitter and receiver built with "nails on a board" and separated by a foot or two of space. This allows the kids to operate the telegraph key on one end and hear the beeps come out magically out of a speaker on the other side! Perhaps two separate boards can be built so they can be carried away as experimentation of transmitting over some distance.

The question now is: what is the absolutely simplest CW transmitter and receiver circuits? The frequency doesn't matter and the distance transmitted only needs to be about two feet. I can imagine the transmitter simply being an oscillator and a transistor for output power. The receiver will likely be a little more complex.

I suppose any form of crude "spark-gap" design is out since it has to work with a small battery and minimal parts.

A wired telegraph isn't a bad idea if that's also OK http://www.w1tp.com/perbuild.htm  Substitute a buzzer for the sounder for Morse as we know it (not just clicks).

One form of wireless which is simple is a ground communication system comprising a couple of audio amplifiers and ground stakes. 

Spark gap is actually really simple provided you don't have to build the receiver. Just a relay will do connected to oscillate.  Eg the relay part of this circuit  http://www.historywebsite.co.uk/Museum/Engineering/Electronics/history/sparktx.gif  Add a transformer for a painful electronic shocker.  Or attach it to
two ground probes to transmit through the ground.  Use a crystal earpiece (hard to obtain) or audio amplifier for the receiver.

If you don't have to build the receiver that simplifies things a lot.  You could actually have two old AM radios and use the local oscillator of one as a transmitter.
What you do is you tune one receiver to a weak station at the high end of the band.  Then tune the other radio until you hear a beat note.  Interrupt the battery
supply to transmit Morse.  Super simple - just a bit of circuit board in the battery compartment might work - almost no construction.

Two $5 Chinese Pixie kits is probably about the simplest for  tx/rx link. Otherwise a 1 transistor crystal oscillator on 3.58 MHz and another crystal oscillator used
as the local oscillator for a direct conversion receiver is very simple.  Feeding in audio could make it AM.

It's a school project, not a space shuttle.  Go for the simplest thing that works, will impress the teacher and other kids and get a good mark.  Nothing more. 

[Seekonk]

As a former science fair judge I have seen this more than once.  No one is going to be impressed by this.  A student has to show some understanding of the project and that they learned something.  I got really tired of asking a question and getting back the deer in the headlights look from 70% of the students.  I would have more confidence if he had posted on the board.  I had a couple pages of guidelines I had to follow.

I have a killer science fair project for anyone that is interested, growing plants with ultrasonic sound.  That got me honorable mention at the state science fair at MIT.  I would have done better if I studied!

[meiz2020]

4th grade for kids is a wonderful era of learning new things especially electronics. I remember myself got excited and amazed hearing a real transistor radio worked from scratch as a project though we already have entertainment system during that period.