Before beginning these modifications please consider the following:

1. If you have a ASC_REV_0 kit and you have already constructed it according to the original schematic and you wish to modify it you will have to remove and replace the microprocessor U2. It might be painful, but the easiest and safest way to remove the chip is to cut the leads off immediately next to the body of the chip and then unsolder the individual pins. Clean off the remaining solder with solder wick. You can order the USB chip, with the bootloader pre-programmed into it by pressing this button: 
2. If you have not assembled your ASC_REV_0 kit please set the microprocessor chip to the side (most likely PIC16F873, there were some options) and order the chip as outlined in paragraph 1, above.
3. There is a way for those who have the programming equipment to program the bootloader into their own chip (PIC18F2550), use these instructions for that circumstance.
   

The ASC (Analog Serial Controller) board can be re-targeted to provide the USB interface instead of the serial interface for which it was originally designed. The process is actually quite straight forward and the modifications are outlined below with pictures to assist. This is a switch in mid stream and I will try to accommodate any of you who have purchased Foundation Kits or Serial Controller Kit to make it as painless as possible.

There are several advantages of using the USB bus. First and most important is that it is compatible with modern computers and should continue to be compatible for many years in the future. It is faster than the serial and parallel ports that have largely been eliminated (relegated to legacy status) from most computers being shipped today and especially on laptop computers, perhaps the most likely to be used with this project.

The USB bus does come with some complication and mystique which can be largely ignored these days with the advent of single chip microprocessors with the USB peripheral interface incorporated into the chip.

So, without further ado, lets take an ASC board and preform a little surgery and turn it into an ASC_USB board. The first step is to remove three traces on the top of the board and three traces on the bottom of the board. If you have any doubt about which is the top and bottom of the board, the top of board looks like this:

The normal copper pattern is shown above, you need to remove traces highlighted in red. I recommend using a sharp Exacto knife to cut the traces at each end of a red line and then I suggest that you work your knife under one end or the other and lift and strip the trace off of the board.

The same is done for three traces on the bottom of the board and again if you have any doubt about which is the bottom match it to the picture below and make the modifications shown in red.

I now recommend that you assemble the board by applying paste to the top side of the board and placing the components according to the schematic below. Lines in red on the schematic are to be added with fine guage (30 AWG Kynar) wire to be supplied in future kit shipments. Some parts are not required after the USB modifications are made. In particular the board is powered by the USB bus and therefore the power supply regulator and input filtering is not provided.

Shown in the pictures below are instructions for modifying the PIC microprocessor to fit the foot print of the U2 postion on the board. The pictures depict a chip from a previous revision and you should be modifying and installing a PIC18F2550 instead of the one shown in these pictures.

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Modification of the microprocessor used on the Analog Serial Controller (ASC_USB_Rev0).

	The foot print for the microprocessor on the Analog Serial Controller board is designed for a package for which there is no compatible PIC micropressors. This is the microprocessor as you have received it in your kit. It must be modified to fit into the available footprint, U2.
	First, make sure that you are working at a anti-static workspace. Second, using a pair of needle nose pliers, carefully straighten out each pin. The pins are made of soft material, so be careful not to squeeze the pin very hard.
	The next process is to form all of the pins into what is similiar to a J-Lead (another style of surface mount chip). I have found that this can be done by placing the package along one long side, perpendicular to the worksurface. Using a reasonable amount of force, roll the chip so that the  pins are curled under the package. Flip the chip over and repeat the processos on the second row of pins.
	The bottom of the package should look similiar to this picture. Take a moment to make sure that all pins are squeesed so that they are close to the package. Also check each pin so that it points to the pin directly across the package from it. This completes the modification. The modified package will now fit on the available footprint. It's not pertty but it works.
	In a different light I discovered something that could cause problems. Please check to make sure that you do not have any whiskers of metal like the one between the third and fourth pins from the right in the foreground. It can be removed by a small pick like tool.

Download Schematic

Now comes perhaps the most demanding part of the procedure, adding the wires to complete the conversion. In the picture below you will see five white wires (contrasted against the blue board they should be quite visible). There are two additional wires not shown in this photo graph that also should be added from U2 pin 18 to P1 pin 3 and from U2 pin 17 to P1 pin 4.

Take a look at the board, in almost the exact center on the right hand extreme margin notice that there is a capacitor. The capacitor is connected from U2 pin 14 and is connected to ground by soldering it between the chip pin and the exposed ground around the periphery of the board. If the perspective of the board looks a little funny it's because I've rotated it to match the diagrams above and so it reads right side up.

Your kit should have a 20.0000 MHz crystal with it and the board above has the original crystal mounted in it, they both work and I have included the 20.0000 MHz crystal for consistency. The original crystal provided an exact multiple of the baud rate selected but since the serial interface is not used in this application that is no longer a requirement.