Understanding Transistors

So what does electronics have to do with Laminar flow fountain nozzles? EVERYTHING! I think I have the nozzle design pretty much nailed down. There are still a few question that I need to answer but those will come in time. I have to wait on some manufacturers to give me some quotes on making my brass nozzle orfice before I can make more progress on the nozzle. So my attention has been turned to the cutter valve. I've been doing a lot of research on this and I've found out that they don't cut the water before the nozzle they cut it after it leaves the nozzle. Why? My suspisions are that they have to in order to make it look clean and cut. If you have a valve that shuts off the water before hand then it won't have a clean cut to it and most likely will slowly die down. Likewise, when you open the valve it would take a second for it to start back up again.

So I've been researching motors, solenoids, and servos (which I guess technically they fit under the motor category, but it sounds more impressive if I have more categories). I started with solenoids because solenoids are CHEAP. I found some on a website for $0.99. WOW! I never knew that, but I guess that makes sense. It's just a couple of windings around an iron core. I have 8 on their way, and I should have ordered more since they were so cheap.

So a solenoid is just a push/pull type of motor. Actually it just pushes or pulls but not both. There is a spring that helps the shaft return back to its orginal position. My microcontroller that I am going to use to open and close the cutter valves can only output 5V and 40mA. So I need a way to get the voltage and the current up so that I can actuate the solenoid.

That's were the Transistor comes in. I read about them in the past, but never understood them. This time had to be different. So I went to radio shack and picked up a couple of different transistor based on my research. Since I don't have my solenoids I subsituted a DC motor that operates at 12V. I put everything together like I read. And it WORKED, kind of.....it worked but slowly. This wasn't good enough because I knew that the solenoid would need to draw more current than was being supplied to the DC motor. So it was back to the drawing boards. I looked over and over again trying to figure out what was wrong. As it turns out I'm not exactly sure what I was doing wrong, but I must have been hooking it up wrong or something. What I ended up doing was ripping everything out of my breadboard and started hooking things back up. When I turned it on everything was working just fine! I don't get it. I SWEAR I was hooking it up properly before! Oh well, at least now I have a working example to work from. I made sure to document everything I did so I can reproduce it in the future.

I ended up still using the TIP31 or TIP31A (I can't remember which one). I hooked the 12V to the motor and then the motor to the collector. The emitter was hooked directly to ground. The uC was hooked to the base via a 2K resistor. I made sure that the ground used for the uC was connected to the 12V ground so that I had a common ground.