Hi,
This may be a tricky one and confusing. Well, I'm confused.
I have a UNO which I used to make a simple data-logger, but it's a terrible waste of a whole Arduino.
Now I have aquired an ATTINY 45. I need 4 channels of A/D and the Tiny45 looks like a workable solution.
Now, stricly speaking, this may not be an Arduino problem; more AVR, but here goes.
I can program the Tiny45 to collect the data using the UNO as an ISP,
but then I have to send the data to the pc ( I've been using Bray-hyperterminal and I reckon it's
brilliant ).
The Tinys dont have a USB UART, so you have to do it another way and that is where I'm stumbling.
The '45 does have USI, but I havnt found explanatioins of how to implement it terribly easy to follow.
However, there is a website called 'V-USB'. Are you familiar with it? It looks promising.
One of the projects on V-USB is a datalogger using a '45 ( EasyLogger )
The USB port connects to INT0 and INT1 ( whatever they are ). I notice that these are also MOSI and MISO.
So, can you actually program this chip using the USB port? Using Atmel Studio I suppose.
The software routine presumably just implements the USB port, but I still need to load it with my own data-logging program.
If you really need INT0 and INT1, the ATtiny45 is not enough as it has only one external interrupt (INT0).
You seem to have a strange definition of data logger. Usually this defines a device that gets data serially or by any other means (analog input, sensors or the like) and write it to an SD card. You seem to get data from the analog inputs and simply transmit them to the PC, is that right?
USI is an implementation of high speed serial buses as I2C and SPI but not UART (to my knowledge). V-USB does implement a USB device in software but the minimal clock speed is 12 MHz. Are you running your ATtiny at least at that rate? If you really get 4 analog inputs and you wanna connect the two USB lines, where do you put your crystal on the ATtiny? It has only 8 pins.
You maybe right, that an UNO is a bit much for a simple logger but in your case it seems more appropriate than a ATtiny45.