Introduction: Trash Coil Driver
This is a generic MOSFET drive circuit, intended to aid building motors from found parts that can be controlled by digital electronics, and powered off of USB LiPo batteries. It is intended, as are all circuits found here, to be a blend of art and technology that contains information about itself that allows it to self-replicate using electronics enthusiasts as a vector for transmission.
What you need are:
A MOSFET that can handle at least an amp of current
a big burly diode
a 10k axial resistor
a soldering iron
paper, pen, or pencil markers or crayons or colored pencils or paint, cardboard
a broken USB cable with the USB A end still connected
broken electronics with a button, the kind with metal and plastic
Step 1: Connect Positive Channel Lead(drain) of MOSFET to Anode of Diode
I am using the IRF7862, a popular MOSFET used in some Sparkfun projects. I have a ton of old circuit boards from a company I had that used these in a product so I salvage those with a heat gun but you can also buy them from any online electronics retailer. Pin one is marked with a little white circle on the black background of the "top" of the device. The cathode of the diode is marked with a white line, and we want the anode connected to the transistor, so the white stripe should be on the opposite end of the diode from the transistor. Since all pins on the side opposite the white circle on the FET are connected to drain, what we want to do is connect all those to the diode lead opposite the white line, all of which is shown in the images here. Lay these out on a non metallic non flammable, or at least not very flammable, as I use a wood door for all of this. Then with the solder in one hand and the soldering iron in the other, make a giant blob of solder over all four leads on the FET package and the diode lead that you're connecting to it.
Step 2: Add Pull-down Resistor From Gate to Source
This is what will keep the thing from going high randomly as the super high impedance input floats around in voltage. Now it won't float. Connect a 10k axial resistor as shown. This takes some practice, examine the images here very closely, try it, repeat, play with using the bend of the resistor to make your life easier. Double and triple check for shorts between the gate connection and the source leads. It's very easy to blob the solder across that gap by accident and that makes the digital input into a dead short! Don't do that.
Step 3: Harvest the Buttons
I like to use an old VCR or tape recorder, they have tons of weird buttons all over. I rip it all apart with a pliers until I can see that the button leads are connected to nothing but the button, and solder leads clipped off of random resistors to make leads on this button.
Step 4: Connect Button and USB Power Cable
With the button in hand, you want to solder those leads to the cathode(white stripe end) of the diode and to the input side of the resistor, which should go to the gate of the transistor, the corner on the same side as the white circle but farthest away from it on that side(pin 4). Add the USB cable as shown, soldering the red wire to the cathode of the diode and the black wire to the side of the resistor that goes to pins 1,2, and 3 of the FET. Remove the unused wires for the USB signal.
Step 5: Add Art and Documentation
Draw a schematic on paper, color code with crayon or marker or colored pencil or paint, add URL to further information on how to duplicate, add paper documentation and art to cardboard backing for support and strain relief
Step 6: Punch Holes in Cardboard, Attach Circuit to Board
An xacto knife is ideal but scissors will do or a pocket knife. Cut some holes, and wrap all around with some scrap wire(with insulation!) or skip the holes and use strips of duct tape at strategic locations, until it's all secure and strain relieved.
Step 7: Connect to Trash Coil Documented Elsewhere
This is a coil intended for use with 5 volt USB batteries, so it's at least 10 Ohms to keep current at 500 mA or below. Solder the ends of the coil to the two leads of the diode.
Step 8: Test, Grow
To test, connect to USB battery, place a small rare earth magnet inside the coil, and hit the button a few times. You should be able to make the magnet jump and move around. If not go back and check all connections and repeat. Then make tons of them, document them and spread and we will have a feedstock that can go into robotic systems made from trash scaleably.
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