[ Log In ]
[ Register ]
Step 21: Driver Caps, Resistor Networks and Mosfets
This tutorial is dated, if you are considering a CNC for your personal use, we would highly recommend purchasing a kit that is very stable from our wide range of machines available. The resistors are in, right? Ah, I know, you want to see the complete assembly before you dig in. Ok, on to this part of the assembly. Please don't ask me what Mosfets are, but the word sound cool! I can tell you that they stand for Metal Oxide Semiconductor Field Effect Transistor. I have personally read about fifty descriptions of this electronic animal and I still can't figure it out. It doesn't say much for a Berkeley grad! Well, I'm open to some plain English interpretations without the word "drain" in them. Are you still with me?


Thanks to David K. A much more understandable description is provided:

        A                     B                     C

      ____|___    _______|______   ____|____

------------| |------------------| |------------

          | N |_________P________| N |

Two N-type semiconductor regions are sunk into a P-type substrate. If a voltage is applied in either direction between A and C, the PN junctions will act as diodes, one forward biased and one reverse biased. Therefore, no current will flow. Applying a positive voltage to the B contact will drive the positive charge down and out of the region between the A and C contacts, temporarily making it N-type. The electric field of the B contact is what causes the charge to move, thus Field Effect. So in effect, you have a single continuous N-type region, and current can flow. The higher the voltage on B, the more P-charge moves, the thicker the resulting N region, and the more current can flow. The A contact is called the Source, where you connect the signal you want to control, the B contact is called the Gate, which is probably pretty obvious, and the C contact? Well, I can't tell you what it's called, because you don't want to hear the word.

David is an avid viewer that is taking on this project successfully, you will see his creation on the upcoming "Creations Gallery" page.

Ok, first we will install the tiny capacitors. I do know what these suckers do. Suckers.. get it? Capacitors stores electricity much like a battery. When the electricity reaches a certain level, it passes through. This component is usually used to filter electricity flowing through a circuit, or flattens out ripples in a circuit, usually to provide a nice direct current or (DC for short) (along with diodes, of course). Diodes and rectifiers will be discussed when we get into the power supply. Oh, yeah, I just received my transformer, and I gotta tell you, IT'S HEAVY. I got killed on shipping! Someone tell me if there is a source for 24v 10a transformers in Houston, TX.

Also, resistor networks and the mysterious mosfets are installed. These, unlike the previous components installed (caps and resistors) need to be installed with a specific orientation. The PCB (printed circuit board) guides this orientation with it's silkscreen layer. A printed circuit board is a material that has traces (lines) of conductive material (copper) that allow the transmission of electricity. A silkscreen is an old fashioned method of putting snazzy ink on a surface with, you guessed it, a screen of silk that also has a layer of material through which ink cannot pass. Silk-screening is not usually used in the PCB manufacturing process anymore, but the naming convention stuck. The silkscreen layer is the helpful text and symbols on the PCB.

I used the solder wick on this video to remove a solder bridge. A bridge is solder that connected to two leads. Removal is easy with the wick. Since we're talking about things that went wrong, something went horribly wrong! I installed and soldered the last RN (Resistor Network) in RN4, even though the instructions point out clearly not to do it. I guess I was caught up in the moment. Well, in a later video, I will show you how I made amends to that situation. I will tell you this, all but one of the leads got forced off, but I still got it to work perfectly. Can't wait to show you!