The classic "Winky Blink" as used in British Columbia school shops for decades. Want to make the Grade 9's giggle? Tell them it's an "astable multivibrator".

R1, R2: 470 ohm (roughly... higher value is dimmer LED)

R3, R4: 56k (roughly... higher value is a slower blink)

C1,C2: 10u (roughly... higher value is slower blink)

Q1,Q2: NPN Transistor (Typically 2n3904, but a 2n2222 will work great, too... just get the pins in the right holes)

D1: Any standard rectifier diode... mostly there so you can talk about what diodes are

LED1, LED2: Standard 5mm LEDs, of the colour of your choice

S1: Can be omitted and just solder over the two pads, but if you want a way to turn it off, a small SPDT switch with 0.100" pin pitch works great

The extra, larger, holes are for a strain relief for the 9V battery clip. Thread the wire through these two holes before soldering it and it will stay attached much longer.

There are MANY good designs for this board. On this one I maximized pad-pad spacing to prevent solder bridges. The down side is that the capacitors and transistors will not sit perfectly flush to the board.

For a video on how this circuit works and how to breadboard it, check out my Youtube Playlist at https://www.youtube.com/playlist?list=PLeAD1slKyItZr_ESeVVBkxTOFCXKUX6hh