Hi, I have a problem with L293D. On Vcc2 is 5V, but on JP1, JP2 is only 3V.
you will see your output will be between VCC2 - 1.4 and VCC2 - 1.8. Your 3V out is pretty close to the low side, and, therefore expected.
You will probably also loose 0.7V on the input diode.
Good catch, Geir. I didn't notice the input diode on VCC2.
That will drop about 0.7V, plus the drop of the h-bridge itself easily explains why he is only getting 3V to the motors.
Try a higher voltage for VCC2. Maybe a 7.2V NiMH battery.
And with SN754410 it will be the same? I know about the 0.7V on diode and 5V - 0.7V = 4.3V , but on out was only 3V, something what I did not expect :D .
Check the datasheet for the SN754410. I think you will find it is about the same. They are both transistor based h-bridge circuits.
The P-N junction of a diode or transistor is about 0.7V. Since the circuit drops through two transistors to run the motor, that's about 1.4V, in theory. The actual drop can be higher.
I am not positive, but, it would seem to me that with HIGH being less that VCC2, and, LOW being more than 0V. Your motors will never see full VCC2. I would guess that you will only see the swing from VOH to VOL. So, your reading was only telling half the story.