This blog post is about determining the value of the base resistor of a MMBT3904L, which is ON Semiconductor's variant of the general purpose 2N3904 NPN Bipolar Junction Transistor (BJT), when used as a switch. The value is determined when the transistor is in the common emitter configuration. Sounds like a simple task and so it should be too. However, as we have commented many a time in our blog posts tasks that appear to be easy never are. Hence, while undertaking this task we decided to follow Lao Tzu's (Who? - Ed) advice, which he elegantly formulated in the following quote:
Do the difficult things while they are easy and do the great things while they are small. A journey of a thousand miles must begin with a single step - Lao Tzu.
So, as he has suggested the sensible approach in determining the value of the resistance of the base resistor of a BJT is to perform the calculation a step at a time, as we demonstrate below.
To me all similarly priced servo motors look the same and promise the same performance and maybe they ought to, too. So amongst all the servos out there how do you choose that perfect one for your application? Well, I suppose that is the question that needs answering! Quite fortunately when I had to answer that question, of which set of motors to choose for the 17 Degree-of-Freedom (DOF) robot project, the Tower Pro MG996R motors came recommended, as part of the 17 DOF robot kit. Hence, these motors were thrust upon me.
The predecessor to this motor, the MG996, did not receive the most glowing of reviews and was particularly noted for its lack of accuracy and centering. However this version is meant to be a worthy successor with a redesigned PCB and Integrated Circuit (IC) control system, which makes it more accurate. We provide an insider's view of this servo in this blog post.