# Voltage divider help

Discussion in 'Homework Help' started by brianmay27, Oct 7, 2011.

1. ### brianmay27 Thread Starter New Member

Oct 7, 2011
7
0
The project for the class is to design a "voltmeter" using op-amps. We need to have 9 segments (>0V, 1V, 2V, 3V ...) so I need to setup a voltage divider to each op-amp to give it a base voltage.

For simplicity I would like to create it so I can setup a series of resistors that would drop the voltage by 1V each segment. My source voltage is 9V.
How would I go about this. I know how to setup voltage division but I dont know how to do it when I need it to drop 1V each time. If someone could help get me off the floor with this it would be much help.

TIA

2. ### BillO Distinguished Member

Nov 24, 2008
985
136
I hate to say this, but this should be easy (trivial) for anyone that knows Ohm's law. Can you least take a stab at it and post your solution so we can see where you are going wrong in your thinking?

3. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,436
1,626
If you string n equal resistors in series and drive them with voltage V, each resistors will have a drop of V/n volts.

Thus, if you string 9 1K resistors and drive with 9V you will get voltages of 0V, 1V, 2V,... 7V, 8V out.

If you use this to drive op amps as comparators the 0V output will always be tripped.

You'll need a good modern rail-to-rail op amp for this. No 741's need apply.

4. ### brianmay27 Thread Starter New Member

Oct 7, 2011
7
0
Great, I was thinking on the bus ride back of how to do this and what you said about summed up what I was thinking.

Thanks again!