How do I use voltage divider?

Other Hardware General Electronics
1

I bought HiTec HS 322HD servo motor. It requires 4.5 to 6V to operate. I want to use 9V battery. Iknow , I could use 3 - 1.5 volt batteries, but I am stubborn
and stupid as well, so I want to use two resistors (with 9v battery) say 330 and 220 ohms and divide voltage into 3.2 and 4.8 volts. But when I connect the
motor then the motor resistance works in parallel with 4.8 volts and the voltage division will change. If motor internal resistance is close to zero (which I
suspect may be the case) than my divider no longer works. If this is true then how do you use current divider to split the voltage? And if the resistance
is not close to zero, should I simply recalculate and adjust values based on the actual resistance?

Then I got clever and tried to measure servo resistance. The ohmmeter reading went from 41MOhm down to about 21MOhms and started slowly to climb
back. I was shocked (not really).

I am trying to learn electronics, robotics and arduino at the same time, and having a tough time to make sense of all of it. Can somebody enlighten
me a bit? Pleeese.

2

Voltage dividers are only good as a reference and not a source.

Either use a lower-rated battery or an appropriately large voltage regulator.

3

Like you said... the motor has a very low resistance. So it's the path of least resistance.

If you want to use a resistance to drop the voltage you need to have a steady current (which you can't guarantee unless the motor spins empty all the time) and calculate how many Ohms would be required to create a 3V drop at the current that the motor takes to spin.

However, I do not think you should even try this. Get a voltage regulator and use it before the motor.

4

id just use a simple 6v regulator :slight_smile:

5

A typical 5V regulator like 7805 should be easy to find. If you are trying to make servo run as fast and as strong as possible then use LM317 and pick resistors for 6 Volts.

Voltage regulators are a basic component you should have if you continue to do projects.

DISCLAIMER: Mentioning stuff from my own shop...

To have "Stuff" to work with you might get the assortment of 30 voltage regulators here: http://arduino-direct.com/sunshop/index.php?l=product_list&c=36

6

Thanks to all who responded. I went to Radio Shack and bought 7805
5V voltage regulator (les than $2). Having already capacitors at home
I built voltage regulator gizmo on the protoboard. I connected battery
(8.4 V dc as measured) and checked the output. It was 4.85 V dc.
Les