Computer and micro-controller communication

After my digital thermometer, I thought it is worthwhile to integrate my micro controller (uC) projects to my computer. There are tonnes of advantages that I see by doing this. While working uCs, specially as being a computer programmer, I found it difficult to achieve a number of stuff. Most basic things like input / output aren't readily available (note that I'm not blaming the uCs here; after all we are not writing software here, but building hardware) -- this makes it very difficult to debug or build prototypes. These days I use LEDs (and different blink rates) to debug various scenarios. But imagine how I would have debugged my first LED blink project :) -- there was simply no way. Not just debugging, allowing uC to talk to the computer (when required) opens up a whole new world of communication. There are so many features that become readily available, like

• keyboard - I can configure my uC parameters at runtime from my keyboard?
• monitor - I can send some debug output or runtime logs to my comp and record it?, you know much work I did to show just 2 digits in hardware.
• processing power - not sure how useful it is but if I need I can make use of the huge processing power a comp has.
• internet - this is very interesting. maybe my uC doesn't need internet but how about controlling my uC from the internet ?? maybe, controlling my room's lights from office ? office -> internet -> webserver on my home comp -> uC -> light; I think this opens up a lot of new opportunities.

Let's see how it evolves :) I have no idea about how I'm going to utilize, but I'm convinced that given my programming knowledge on computers, it is quite a useful thing to have. Technologies becomes more and more powerful only when they interact.

Now that we are convinced that a computer interface is useful, it is time think about the choices. The possible options are serial port, parallel port, USB, bluetooth, infra-red. Bluetooth and infra-red need hardware counterpart on both sides (on the computer and uC hardware), so that isn't practical for me now. USB seems a option, but that also requires a USB protocol handler on the uC side (there are some free open source USB drivers available for AVR uC's but they would occupy considerable code space -- and with just 8KB available for programming, I would rethink). Serial and parallel ports are the simplest options. Over these two I prefer serial port for two reasons.

1. Serial port requires fewer number of lines for transmission/reception (technically only 2 lines for data(tx/rx), but additional lines for vcc,gnd etc., add up to 4-5 lines, still much better than parallel port).
2. ATMega8 has builtin support for handling USART - the standard serial transmission protocol. This makes it handy for us to talk over serial port between the computer and the uC.

So I chose serial port as the preferred communication interface. This does not mean that I can just connect a few wires from serial port of the computer to my uC -- because the logic levels are different between the serial port and the uC. I need a convertor for these logic levels before I can communicate. How? stay tuned.