Let's Make Robots!

transistors

Light following robot

Hey there guys. Well I found this project here on this site and i wanted help since it doesn't work. I already tried it 4 times and yet nothing happens. Since I'm new to this, I don't really know how to read robot schematics. Maybe I did something wrong with the circuit and since I do not know how to use a transistor. Please please please help T^T

Plays Naughts and Crosses (Tic Tac Toe)
This robot was created as an entry for Oddbot's challenge: http://letsmakerobots.com/node/35296 I learned a lot with this project: just check out the Reflection … Read more
Infrared diodes and detectors make things fun and magical. We are use to touching or flipping a switch to turn on lights. A simple transistor circuit with an … Read more

Choosing a transistor

I've used two types of NPN transistors in the projects I've done so far and I've tried to investigate why, but my conclusion just doesn't seem to make sense (actually, I'm not sure if I've reached one...).

For use with an Arduino, I've used a PN2222 transistor:

 

Whereas, for BEAM solar bots, I've used the 2N3904:

 

Transistors -[Page 3] Switches, common or uncommon

[Added note: while I had intended to add more to this series of pages, to explain FETs (jfet, mosfet, etc.) and so on, I have decided at least for now to not do so. I realised I would just be "reinventing the wheel" as the saying goes, when there are already so many good books on the subject.

hello i want to know if my circuit would work in real life

hello
im building a flashing heart for my girlfriend, im using a 555 chip and 7 LEDs

i have a circuit lay out from multisim it says it will work but i have my doubts 

 i wanted the potentiometer to change how fast the LEDS flash on  multisim  its always the same soo im not sure why 


im using 10 mm LEDs  

Help with H-Bridge

 Hello, I need some help to reduce the chances of burning my precious Arduino/apartment.
 
I managed to build and test this H-bridge