Connecting the hardware
If you haven't yet configured your coin acceptor, please visit this page for instructions on how to do so before continuing on with the project.
Note that there is no configuration required for the printer; we're going to use that as it comes from the factory.
You'll need to put headers on the Arduino Pro Mini before moving forward. I usually insert the headers in the breadboard, then place the Pro Mini on them, then solder the header in place. That way, they're nice and straight.
For the programming end, you can solder them on perpendicular to the board, or parallel to the board. Your choice.
There are three wiring harnesses for this project: two for the printer and one for the coin acceptor. We'll need to prepare these wires to be inserted into the breadboard. While you can simply strip the end and cram it into the breadboard, the result is unreliable and can cause problems down the line as strands of the wire break free and move around inside the breadboard.
My standard method is to place a row of header pins into a "third hand" type of tool and "tin" the short side of the header pins by touching the soldering iron to the pin, then touching a bit of solder to the pin. This will cause a bit of solder to flow onto the pin.
Then, put about 1/2" (12mm) of small diameter heat shrink over each wire and strip about 1/4" (6mm) of the insulation off each wire. Place the wires, one at a time, in the third hand, then tin the ends of the wire. By tinning the ends of the pins and wires, you eliminate the need to hold wire, solder, and iron all at once.
With the header pins still in the third hand, touch the tinned pins with the soldering iron until the solder melts, then touch the tinned end of the wire to the pin. The solder on the pin and the solder on the wire will flow together; remove the iron and let the solder cool before releasing the wire.
Once all the wires are soldered on, slide the heat shrink tubing (you did put that on the wire before soldering it to the pins, right?) down to the solder joint and shrink it with your choice of heat source. Once the heat shrink is in place, pull the pins free of the plastic holder that keeps them in line, and you've got wires that can easily be inserted in a breadboard.
I've include some crimp connectors in the wish list for this project; you can certainly avoid using them and simply solder the ends of the jumper wires directly to the tabs on the button. Tin the pin on the end of the jumper wire, the tab on the button, and connect them the way you did the header pins on the wiring harnesses.
To use the crimp connectors, I cut one of the pins off of a jumper wire, stripped about 1/2" (12mm) of insulation off the end of the wire, folded that back on itself and put a big glob of solder on the bare wire. That will give the crimp something firm to hold onto.
Slide the bare end of the wire into the crimp connector from the open end. Slide it in until it protrudes slightly from the narrowed side, closer to the spade end than the open end. Pinch the narrow part of the connector down tightly; it takes some real effort to be sure the crimp is secure. A couple of tugs on the wire will show whether it's tight enough.
Assemble the parts according to the diagram above. Note that a couple of the wires from the coin acceptor and printer are left floating; you can either cut those wires short, plug them into an unused row on the breadboard (but not all in the same row!), or cap them with more heat shrink.