I've spent a lot of time learning about microcontrollers and very little time working with analog electronics. Wanting to change that, the first circuit I've been exploring is the Astable Multivibrator. It's a set of RC time constants connected to each other, as one charges, it triggers a transistor that discharges the other. The system is never stable so the result is lights tha flash in an alternating pattern.
Note: This project has been submitted to the 2017 Hackaday Prize but it is not eligible for judging since it was built by a member of the Hackaday staff. The project was submitted as a way to test out and make tutorials for other people to use as a guide when working on their Prize entries.
This project uses very few components to build a clever little analog blinker.
And you might find it interesting to see the circuit simulation:
The oscilloscope output clearly shows the ramp of the base of one of the transistor and the square wave that results on one of the LEDs:
If you're powering a project from a 9V battery, you can salvage a suitable connector from a dead 9V.
Grab your bucked of dead batteries and search through it for 9V
Choose one that doesn't have a buildup of blue corrosion on it
Remove the sheet metal case being careful not to cut yourself. This battery has flat cells in it, but occasionally you'll find six cylindrical cells. There will always be six of them because each cell adds 1.5V to the overall output.
Liberate the connector for your own purposes. Soldering wires to these can be a challenge. I recommend roughing up the surface first with a dremel or coarse sand paper and adding a blob of solder before trying to connect a wire or component lead.