Step 6Mounting the components

To keep the project the same size as a normal prox card, I decided to make it on a small PCB that was the same size as a business card.

I decided to use surface mount push buttons that I brought from eBay, so that meant that all of the components must be soldered onto the copper side of the PCB to allow the buttons to be mounted and labeled.

I started by soldering the push buttons, then I mounted the LEDs, resistors and capacitors.  I had to install the 16MHz crystal on the bottom of the PCB, as I did not have a surface mount crystal.  I also installed 12 jumpers on the back of the card to connect the key columns together.

The ATMega168 was mounted next.  I did not use a socket, as I wanted to reduce the board thickness. 

Next, I wound the coil - I used a piece of scrap timber, with 4 screws mounted on it, and counted 100 turns of 0.25mm diameter coil winding wire.  Before I removed the coil from the mounts, I wound a small amount of clear tape around each edge to make sure that the coil didn't unwind.

Then, I mounted the coil on the back of the PCB, along with a small battery holder.

I was pretty happy with the result of my handiwork.