1
Why can't I use a potentiometer to get a different voltage?
2
===========================================================
4
Suppose that you have 12V and you need 6V. Why can't you use an
5
arrangement like this to get your 6Vs?
17
You *do* get 6V, but it isn't actually practical to do this. The
18
problem is that, when R is suitably high, you've limited the current
19
so much that it isn't really useful.
21
And when R is suitably low, there isn't enough resistance between the
22
+12V and 0V rails to prevent a lot of current flowing. Lets work this
23
out (lets suppose that R is 1 ohm).
25
V = IR, therefor I = V/R
26
P = VI = V(V/R) = RV^2 = 1 * 12 ^ 2 = 144W
27
P = VI, therefor I = P/V = 144/12 = 12A
29
That's a lot of current and a lot of power, flowing continuously, just
32
Also, fluctuations in resistance and current drawn on the 6V pin would
33
actually change the ratio of the potentiometer, so you wouldn't get 6V
36
The solution is to use a voltage regulator. The 7805 will give out 5V
37
(so long as you can supply it with at least 7V). But the arduinos
38
already have something similar on-board and so can take an input
39
voltage in the range 6-20V (although 7-12V is recommended).
added
removed
electronics-information
