where i am going is to now if i am doing this well or not
and ok,later i will upload the pictures that i took,but i can´t do it now
the results that i got are these:
when i will say in this post that the square wave has values between two numbers,the higher number is when the wave is in high state, and the low number is when the wave is in low state.
frequencies will be 50hz
i have 2 possibles ways to do this:
1)WITH A POWER OPERATIONAL AMPLIFIER
http://imageshack.us/photo/my-images/401/dudaq.jpg/
first that i did was put a R=10ohm(because motor has max current no load=0.3A and max voltage 3V) instead of the motor, and the results with the oscilloscope at the output of the AO are a square wave with voltages between 0.4 and 3.2V(same wave at the input)
``It look work weel because with these values the average voltage across the motor will be 1.5V for 50% and 2.3V for 75%``
but when i set the motor instead that resistor,i saw with the oscilloscope at the output of the AO a wave with values between 3.2V and 1V(at the input this wave has values between 3V and 0V)
then, here is the problem that: if we calculate the average voltage across the motor,it will be 2V for 50% and almost 3V for 75%, and this is caused about the inductance of the motor,which increases the voltage at the output because now i have 1V when the signal is in low state
so i need to reduce this current consumed for the motor,which is 0.4A for this case,but it can be only 0.3A!! so the only way that i find to do this is put a power resistor in series with the motor
2)WITH 2 TRANSISTORS
http://imageshack.us/photo/my-images/717/darl2.jpg/
i did the same,i put the oscilloscope at the catode of the diode parallel with the motor,becase the value at the anode will be always between 3V or 2.8V
first set a resistor and measure the voltage, the square wave has values between 0.2V and 2.8V
``It look work weel because with these values the average voltage across the motor will be 1.5V for 50% and 2.3V for 75%``
but when i set the motor instead of the resistor,i saw the next squares waves at the catode of the diode:
for duty cycle 50% i see a square wave with values between 1V and 0.2V
for duty cycle 75% i see a square wave with values between 0.8V and 0.2V
for duty cycle 25% i see a square wave with values between 1.4 and 0.2V
then if i subtract the value at the anodo and at the catode,i will have 3-1=2V 3-0.8=2.2 3-1.4=1.6V across the motor
so again the values changed,and they are similar that i saw for the case of the amplifier
i hope that all is clear now,so as you can see with a resistor instead of the motor i have the results which i should have,but when i set the motor, the average voltage in the motor is higher than in the case where i have only the resistor
i think that is normal because of the inductance of the motor,but i thought that it shouldn´t change alot,but it does!! and i don´t know if it is correct