[sdiy] Protecting microcontroller inputs from - voltage?

[Bret Truchan]

Hello!


I took quite a break from designing my analog synth modules, but here I am 
again! I'm still working on a module that uses a microcontroller as it's 
basis. I've successfully used a zener clamp style circuit to limit the 
inputs of the microcontroller to +5 volts. However, I haven't added any 
circuitry to keep the voltage from going negative.


Question #1: I'm assuming that it is _bad_ to allow negative voltage on the 
inputs of a microcontroller. Is this a fair assuption?


Question #2: What's the easiest way to clip out negative voltages?


Question #3: "stupid question": If I have some of the lines of the 
microcontroller defined as outputs, I don't need to protect them from input 
voltage, do I? If someone hooks up voltage to an output line, nothing will 
happen, right?!?


Question #4: Ok, this is a tangent. Wouldn't it be cool if there were an 
online java/flash based web page that you could create schematics with. Once 
you're done, you would be given a long string of printable text like: 
"alb150gja02n50g72ogfoswl". The text would represent the schematic in 
compressed form. You could then post to a forum or e-mail list,


Hey guys, here's the solution! <a href = 
"www.instashematic.com/show?data=alb150gja02n50g72ogfoswl">See Schematic</a>


The website wouldn't need to store your schematic info, so the overhead 
would be very small. :-) Just an idea.

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