Electronic – K150 PIC Programmer on linux with usbpicprog

Compared to AVRs, PICs have a variety of twisty little variations in programming algorithms and interfaces, which require careful study of each "programming interface" document. Been there, done that (up to a limit). Unless you are in it for the thrill I would not recommend it. Get yourself a kit or a pre-built programmer. I sell one, Olin sells a few, and there are the PICkit2 and PICkit3, and the various clones of these two. Take your pic(k). I would recommend a type that is at least capable of in-circuit programming. Unless you are into selling programmed PICs, ex-circuit programming is almost useless.

You can begin by looking at this Texas Instrument application note: MSP430F42x Single Chip Weigh Scale or those design note from Analog Devices: Precision Weigh Scale Design Using the AD7192 24-Bit Sigma-Delta ADC with Internal PGA and Weigh Scale Design. This, also, is a block diagram for a weigh scale.

Basically, you use a load cell, an amplifier and an A/D converter, which feeds the data into the microcontroller.

Then, after this is working, you can work on interfacing it with the computer (some models of the MSP430 have USB support on-chip; other microcontrollers might have this feature too).

As for USB host (needed to store data in an USB thumbdrive), you can use (e.g.) the MAX3421E to add support if your microcontroller don't supports this function.