Look up astable multivibrator or flip flop, two transistors, four resistors and two capacitors - and keep the supply voltage below 6V or so. You can make it run fast for audio, or run slow with a couple of LED's flashing ON and OFF.
I am making a really simple cheap speaker (consisting of bluetooth amplifier ZK-502C, Dayton audio TCP115-4 and Dayton audio ND16FA-4) and i need a capcitor to cut low frequencies for tweeter. Usualy i used a electrolytic or ceramic capacitor to cap it at around 3500Hz. But today i read a guide...
www.electro-tech-online.com
WHATEVER YOU DO MAKE SURE YOU PROTECT THE SOUND CARD INPUTS PER THE LINKS IN THE ABOVE POST URL !
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Now if you want to experiment with Arduino and the like, and new to programming, consider
block programming tools to write code. If you know how to use a 4 function calculator then
in your head you already have a beginning programing basis, the idea of variables (like intermediate
value you store to memory to later recall and operate on), various operations, sequence of operations.....
As above, nothing gets things started with immediate feedback like blinky lights. Start with the 2-transistor classic, because the transistors are operating in their most simple mode, a saturated (on-off) switch. Next, a 555. Next, a 555 plus one transistor to have the LED fade up and down.
Back to the 2- transistor flipflop, attenuate the output into some powered PC speakers and scale the components for midrange audio. As you vary the timing resistor values, the character of the sound will change with the duty cycle. Next, same thing with a 555. There is an astable circuit variant with 2 diodes and one pot that lets you change the duty cycle while holding a constant frequency. Very 1980's synth.
I would start by giving them a D cell battery and a small electric motor - make sure they understand what a circuit is
Then the same with an LED and a 3v coin cell. See if they can get it to light. The internal resistance of the coin cell prevents too much current from damaging the LED
Then have them put on some safety glasses and give them two D cell or AA batteries and an LED (or you can demonstrate it). The LED will flash and go out, it may emit some magic smoke or even crack the outer lens). But have them lear that some components are sensitive. This experiment will kill the LED!
Then give them a 100ohm resistor to put in series with the two 1.5v batteries (D or AA). Have them look into the LED installed one direction, then the other (diodes only work in one direction).
Have them add a switch in series.
Have them design a circuit for 2 or 3 LEDs (let them figure out parallel). Have them work in teams to use additional batteries to make 2 or 3 light in series.
start simple and hands-on! Make sure they understand what each part does. Many kids really have aha moments with these simple exercises that seem so obvious to us. The motor seems most fascinating to most of them. You can buy handfuls of small motors for very low prices on Amazon.