[sdiy] Protecting microcontroller inputs from - voltage?

[Ken Stone]

>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.

If you have the zener clamp wired with its anode to zero volts and its
cathode to the input line, you already have protection for negative input
voltages, as the zener will be forward biased if the voltage goes negative.
As mentioned in the other replies, some sort of current limiting resistor is
needed in line.

>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?!?

It's still the same circuitry connected to the pin - just operating in a
different mode, so the requirements are the same.


Ken
_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au  
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
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