isolating two blocks from eachother

my problem is that i'm using two voltage dividers in a circuit ..... both r getting effected by each other.... is there any way that i could isolate them from each other..... i've explained the matter in a better way in the image.....


the frequency of the square wave is 300bps.....

plz help....and keep it as simple as possible and briefly explain the solution too..... thanks

problem 2:
at some other place i've a 300bps square wave which has 2.5V as lo and 3V as hi..... i want to change it to a 0-5 square wave..... how would i achieve this???? i thought of achieving it in two steps... first bring the lo voltage back to 0V, like remove the DC component and then amplify it to 5V using a single supply op amp...... plz comment if there is a better solution.....

someone plz reply i need to solve this

use transistor as switching and you can achieve all your need by controlling base biasing (its recommended you to know potential dividing biasing ) OP-AMP can Also help in Best way for 2nd prob
also refer this link
http://www.zen22142.zen.co.uk/Design/bjtbias.htm
:-)

kazim,
always note that when u generate a voltage source,the internal impedance of the source carries a significant part in the design and it should be very low compared to the load connected to it ( an ideal case would be zero impedance which is practically impossible). So in ur case, when u used a voltage divider, the internal impedance is significantly high. Try using a adjustable zener circuit ( a TL431 would suffice) instead of the 1k resistor in the voltage divider to generate the 4V source.
:-)