Voltage Regulator IC 7805

Voltage Regulator IC 7805




Let's say you want to play with your Microcontroller today. 

With any IC, you need to power the thing. 

There are two power connections on basic micros : VCC and GND. What the heck is VCC? This is the label for the positive voltage. Don't worry, after a few days of this, seeing 'VCC' will become very normal. GND is short for ground. All electrical current needs a way to flow back to ground. This can be called 'common' but is often just labeled GND.

There are thousands of different micros out there, but 5V (five volts) is the typical VCC. 3.3V is also typical but you'll also see 2.8V and 1.8V VCCs on more exotic micros. For now, just worry about 5V and GND.

Where do I find this 5V?

You need to hook up 5V and GND to your micro. 

Quick note: If you reverse the connection on your micro - bad things happen. Always make sure your 5V power supply is connected to the VCC pins and GND to GND. If you reverse this and connect 5V to GND on the micro and GND to VCC on the micro, things won't explode, probably no smoke, but things will probably heat up like crazy, and you'll probably damage your 250 bucks micro. You probably will. I did. Many times. Try not to do it.

Ok! You need 5V. Time to build a simple voltage regulator circuit!

The most common regulator is called the LM7805. Why? I dunno. I've never actually touched a component with LM7805 stamped on the outside. There's always other letters stamped on the outside like 'LM78X05' or 'LV78X05' or some such crazyiness. Just know that there are many many manufacturers out there and they are all producing the same basic part, with small tweaks to each one. What you need is one of these generic parts that is designated as a '5V linear regulator'.

LM7805

Here you can see the 'pin-out' of the LM7805. Say 'IGO' in your head and commit this to memory (input, ground, output). You'll probably hook up a lot of these. When in doubt, always check the datasheet before hooking up a new part - or else be close to the on/off switch! Input is the input voltage of anything greater than about 7V. GND is ground. Output is the 5V output pin. All grounds need to be connected together for current to flow across the system. One more time - connect all grounds. This is the main reason why a novii can't get a system to work. 

Schematic

Schematic note: The two ground pins are not shown connected. We assume that nets (the green wires) of the same name are connected together. Schematics can get big and complex, so you won't see all the wires together, but in your breadboard you need to connect all the GND pins together. In this case it's the GND wire from your 9V battery (power source) connected to the GND pin on the regulator.

Now, just wire it all up on a breadboard.

Congratulations! You've built up your very first voltage regulator! Now leave this 5V power supply wired in your breadboard! You are going to use it many times...