Volts and Amps... For Dummies
October 14, 2008
It seems that I might be turning into the lay-person lingo translator around here so I thought I would use my new-found position to start posting some basic concepts...
I have noticed a lot of posts about running motors, motor drivers and the like so I thought I would do a post about one simple thing, there may be more to come.
Today's lesson is volts, amps and logic signals.
Here we go...
Volts are water-pressure and amps are the diameter of the pipe.
Volts are guys walking down a hallway and amps are how much each has in his back-pack.
Volts are horsepower and amps are torque.
Volts are PSI and amps are CFM.
High voltage is a light-weight bullet going wicked fast.
High amps is a huge ship at 2 MPH (KPH) slamming into a dock and not stopping
Volts and Amps (Pratical Crap)
You can stuff a crap-load of volts through a tiny wire
Amps need big wires (Jumper-cables for your car, yo)
A lot of amps make things hot.
Volts zap you, amps kill you. (Static electricity is wicked high volts, low amps)
There are lots of math things to calculate in terms of how volts relate to amps but forget that for now. As a basic idea, if you double the volts, you half the amps. For example: I have a tablesaw that I can wire for 110V or 220V. At 110V it sucks 15 amps, at 220V it sucks 7.5 amps.
Volts, Amps and Logic (For your robot brain)
Your robot brain talks to all the other electronic doo-dads using a logic-level signal. This signal is usally 5 volts but very, very low amps. A sonar sensor talks to your brain using a logic-level signal, for example. Seeing that you need some-sorta amperage to run really anything (a motor, light etc.) you will need a driver. A transistor is just a little switch that can talk to your "brain" (using a logic-level signal) and switch bigger things on. A darlington driver is just a bunch of transistors stuck into a neat little chip. A L293D motor driver is a bunch of transistors (stuck in a neat little chip) that are set-up in a way to run 2 motors forward and reverse. Both can take a signal from the brain and turn things on. In terms of servos, you will notice they have 3 wires. 2 wires are power (good power, with some amps -straight from the batteries) but the third is a logic-level signal to tell it what to do.
In a nutshell:
A darlington driver will run (usally) 8 things on or off (and fits on the picaxe 28 board)
A L293D Motordriver will run 2 motors forward AND reverse (Also on the 28 board)
Servos (at least the signal wire) can run directly off the brain (add a 330R resistor on the signal wire) -For more info see the "start here" post -Good stuff
LED's are super tiny, draw tiny amounts of power and you CAN run them directly off the brain.
O.K. That's all you get, and now you know... And knowing is half the battle!