This instructable is a simple and cheap way to make a machine that will automatically stamp papers or whatever you need for either classroom or home use. The total cost of this will be around 70 dollars, the main cost coming from the solenoid which will be around 15-20 and the arduino which is 30-40. The cost of the other materials willl be about 10 dollars total depending on where you get it.
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Step 1: Materials
The main materials you'll need are jumper cables for an arduino or 22mm wires to use for connecting everything. To go along wiith this you'll need the actual arduino which will control the outputs to the solenoid, an uno rev 3 works great but just about any arduino will work as it only acts as a conductor. The solenoid is a push pull type that runs on 12-24V of power, this is a greater amount of power than the arduino can handle so a resistor will be required to limit the amount of current as well as a diode that can handle the voltage to prevent back flow desatroying the circuit. The gates for all these signals is gonna be a TIP 120 transistor which has 3 prongs to input and output signals. Finally solder and a power supply for the arduino are also gonna be usefull, any solder works whichever is easiest for you to use and a plug-in 9V was used for our arduino. Having a bread board to plug everything into will make the wiring significantly easier and require less soldering. The power for the solenoid will be 2 9V batteries in series either by solderig them together or using some sort of clip that you can plug them both into.
Step 2: The Casing
The container of this can be built out of one piece of wood if you wanna cut it or just get each individual part but that will be considerable harder. If you wanna skip all of this just getting a box that will fit the arduino batteries and a small bread board. The dimensions for the toip and bottom are 6"x6" with the sides being two 6"x0.5"x2" and two 5"x0.5"x2". This would be a good time to drill a hole into the top side of one of the smaller side pieces as this is where the plug for the arduino will feed through. This hole size will depend on how you plan on powering the arduino. Drill one more small hole on either the top or bottom wood piece to feed the wires from the solenoid into. Glue 3 of the sides leaving one open as well as the top open to put all the circuitry inside.
Step 3: The Circuit
This is a pretty simple circuit especially when using a bread board. Before anything program the arduino to run the blink command and edit the timing between each activation to whatever feels best for you to properly move papers in and out of the stamper. The arduino has the GND connection going to the blue minus side of the board and the pin 13 to a hole on the row right above that. Connect a 1K ohm resistor to the hole in the row above that one as well and then the other end to another whole further down the same row. This needs to connect to the collector of the transistor while the emitter will go to the ground on the board. The ground of the transistor connects to the ground of the solenoid and the power of the solenoid goes to the power on the board. RIght below the connection of the solenoid to the transistor you must have a diode that connects to the ground of the board to prevent back flow of the current. Finally the batteries that were soldered into a series curcuit will simply be connected into the red plus line for power and the blue negative line for ground to make a complete loop.
Step 4: Final Steps
Gle the breadboard into the box using hot glue or another option of your choosing making sure it's secure. Glue the arduino next to that making sure to line up the power connector with the hole that you drilled earlier. Set the batteries inside and secure them down in anyway that you see fit. Next set the solenoid half an inch above the base of the case to make sure it has enough room to extend and stamp properly and glue it into place. Feed the wires through the hole and plug it into the arduino. Finally you can put the last top piece of wood on leaving a small area to access the batteries for when they need to be changed. Then all you need to do is glue whatever stamp you want on the bottom of the solenoid and plug in the arduino.