Initial Purchasing - Microchip Sampling

Well I have to admit, I am bored today...  We finished the last show last week, and this is now the first day in a while that I've had completely free.  I sat watching TV this morning, rather bored at the lack of anything worth watching and also bored of wasting my life doing nothing, and then started digging through my drawers to find all the old items I purchased, and so I'm now trying to remember back to all the items I wanted to say when I was last doing this project.

Lacking anywhere in particular to start, I'll try and talk a little about Microprocessors, they are afterall integral to the whole project!

So what is a Microprocessor?  Well I guess I could go to the Wikipedia page about them and copy out information, but instead I'll describe what I know about them...

The Microprocessor is going to be a Microchip which acts as the main CPU, (that's Central Processing Unit) for the device we want to create.  This is the main chip which will hold the computer program, control all of the electronics.

When I started with this, about the only thing I knew about various Microchips was the word "PIC".  During my time at university, a number of friends in the Engineering department kept praising this type of Microprocessor, along with talk about various 'programmers' and 'samples'.

In fact when I first decided to look into this project, the idea of people at uni receiving a number of free sample Microprocessors resulted in me getting a little ahead of myself.  Some scanning through google and various web sites led me to the Microchip Samples website.  Being a little ahead of myself, and eager to quickly get into programming something, I made the mistake of randomly selecting four Microchips for free samples.

In hind-sight I really should have thought better for my selection of microchips.  While I can't remember the exact reasoning behind each choice for the chips, I do remember it being a little random, and really full of confusion.  I looked through the list of chips having no clue what-so-ever which chips I wanted to play with.

Surprisingly quickly after ordering my four random chips, I found a nice small box drop through my post containing the four chips, each in their own small tube.  I don't have the box any more but the chips in their tubes are displayed below:

Sadly, once I got programming, (more of that later hopefully), I found that the only chip I found usable was the PIC16F874A chip.  That chip is actually the large 40-pin chip closest to the camera above, and it provided basic process stuff which I managed to get working, although I can't exactly remember why.

Similarly, I can't actually remember what the problem was with the other chips.  I think the 18 pin one may have had an issue with the programmer I got as I needed a certain programming interface, however I'm not sure.  The following were the other three chips I got just in case your interested (yeah right).

 * PIC16F648A - I/P - 18 pin
 * PIC16F873A - I/SP - 28 pin
 * PIC18F2580 - I/SP - 28 pin

Really I should have looked for a chip which included a USB interface as one of my samples.  Once I started investigating more, and thinking more about what I would need for the DMX interface I realised that I would want one Microchip which could handle the USB connection as well as running the DMX signal itself.

Well at the moment that is what I am thinking anyway... Considering I'm currently not certain that I can have one singal chip controlling the output signal as well as reading in the USB buffer signal as well as reading in any input devices and outputting anything to any output devices.  However that being said, only time will tell if one chip will be enough.

After some of my initial investigations, I found the PIC18F2455 chip.  This family of chips include the ability to link to a USB2.0 interface, and (I believe) includes special code within the chip to read in and respond to USB requests using a shared memory buffer.  As a result of this, I decided to buy a few of these chips in the hope that they will be able to do what I want.

Since I was a little worried about blowing any of the chips I bought, and I guess also because each chip is only £2-£3, I settled on buying two of each of the family of chips.  Of course once I'd decided that, I came across another unfamiliarity with technical terms...  What type of chip I should buy, considering there seemed to be a number of options, (PDIP, TQFP, SOIC and QFN)...

After a little investigation, PDIP appeared to be the standard chip I had come to expect.  TQFP was a tiny 44-pin version of the chip containing legs which could be soldered onto a circuit board, (it is tiny, like 1cm square).  SOIC is the 28 pin version of the chip for soldering to a circuit board.

Since I'm just attempting to start programming, I was going to be using breadboard to create circuits on, so the chips I needed were most definitely the PDIP versions of the chips which would actually fit into the breadboard, and require no soldering, (not to mention that the TQFP chips have such small legs that it is probably almost impossible to manually solder them to circuit boards).

I put in an order for two each of all the chips, (there are two 28 pin versions, and two 40 pin versions, for each of the types the difference between the chips is the Program memory size being 32K for one chip and 24K for the other chip).  After finding out that I was only a few quid short of the price required to not pay Postage and Packing, I also added on one 28 pin SOIC version, and one 44-pin TQFP just so I can see how the chips look, for effectively no extra cost, (as without them the P&P cost their price [ish]).

When the chips arrived, I was surprised to find them in one huge box which was much longer than required.  Inside, each chip type came in a long tube containing the two chips in each of them, but it was a nice christmas-like day opening the air-tight packet containing the 44-pin chip.

The picture above shows the box the 10 microchips came in, along with a standard pen so you can get an idea of the size of the box!  Opening the box, (see below), showed there were 4 clear see-through bags containing one tube with 2 chips in it per bag, (one per chip type ordered).  There was one silver bag (which may have been air tight I can't remember) which contained a tube with the 28-pin SOIC chip, and another (definitely air-tight) silver bag containing the 44-pin TQFP chip.

Overall it really felt like a waste of packing space, especially as the original samples came in a nice and small box of the size I was actually expecting!