So I was asked to make a signal mixer (using resistors only) that combines the signals V1, V2 where
V1 is a 1 kHz square wave that varies between 0V and +1V, and
V2 is a 5 kHz sine wave that varies between -1V and +1V
and produce a singal Vout where
Vout= (1/2)*V1 + (1/6)*V2

First of all I have a question
Does it matter what kind of source do we have?
I mean if we had for example a dc source or a square wave with different frequency would we do something different to solve the problem?

I started thinking that my circuit would be something like this
http://i1152.photobucket.com/albums/p495/jimgeor/my_circuit_zpsb14c0033.jpg
and then using the superposition theorem I would get two equations Vout=...*V1 and Vout=...*V2 where ... is two functions of R1 and R2
then I would take the first one equal to 1/2 and the second equal to 1/6
and then I would have a system of two equations
BUT my system has no solutions...
what am I doing wrong?
Can you give me a tip on how I should get start?

ps Congrats for your forum
It's amazing!!

 

The type of source could matter if it's output impedance isn't significantly less than the resistors being used.

It may look like you have two free parameters, R1 and R2, but what happens if you simply multiply R1 and R2 by the same amount? Nothing changes! The only real parameter you have to work with is the ratio of R1/R2.

Try putting a third resistor between your Vout and ground.