I want to take an Arduino and after programming it on the PC like normal via USB, push a button or something and change its mode so that the behaves differently. Is this possible? I'd like to interface with this:
Pins are +1.5V, clock, data, ground. Blue box on top is what I'd like to replace with the arduino. They're using a mini USB connector for the serial connection. Looks like a mutant form of SPI as the clock is from the box (with readout) to the slide and the MISO data comes in reply with clock pulses from the slide. (update: it uses a 21 bit protocol with 9kHz clock and the code from Yuriystoys is almost plug and play)
I'm working on reading the info while in parallel to the connection via wires I soldered to the board's pads.
Update: I ended up soldering a through-hole USB A socket onto a Prototyping board and using that. I routed +3.3V to pin 1, set up a voltage divider for the clock (D6) 330/470Ω on pin 2, routed pin 3 to MISO (D7), and connected ground to pin 4. I'm sure this is physically/electrically impossible to implement using the existing USB port on the board.
While I did get the results I was looking for, the capacitance based scale's reading technology would slowly drift, rendering results inaccurate over time. I need repeatability and drifting .002" in 10 minutes won't cut it. I am reworking this using a 1 micron glass slider scale from DroPros.com and will maintain fixed position in EEPROM between calibrations.
TFT display is Adafruit 1.8" TFT with SD card and 5-way joystick input. An indispensable i/o shield in my opinion; easy to program, easy for user input, and quite versatile.