daGenie, that is a solution, but not a great one (however it is your first genuinely helpful post). [EDIT: No, that's a bit harsh]
There are a couple of problems:
1) the duty cycle varies with frequency
2) the problem is less that you may need to buffer the output than the output if shorted could destroy the 555.
3) using a voltage regulator to limit the voltage is probably not a great idea, but at low frequencies probably not that bad either. It may not be cost effective though
To get a 50% duty cycle you either need to use steering diodes or stop using pin 7 as the discharge pin.
This is the steering diode solution:
This requires 2 resistors to set the frequency (since charge and discharge go through separate resistors. It is possible to add a single pot to control frequency, using the 2 fixed resistors to set the maximum frequency.
Pins 6 and 2 connect to the top of the capacitor and a pot is connected between the junction of R2 and the cathode of the diode and the top of C1. R1 and R2 need to be chosen both to limit the max frequency and also to limit the current through the discharge transistor (see the normal limitations on R1).
And this is the pin 3 solution:
In the latter case, if you don't want variable duty cycle, you can remove R1 and the 2 diodes (replacing them with a link).
The 555 is drawn as a schmitt trigger inverter, because in this circuit that is the function it is performing.
As mentioned earlier, the output of this curcuit should be connected to pin 3 via a resistor to limit fault current and (in the second case) to ensure correct timing under load. This can be connected to a 12V zener with a 5V zener switched in parallel to give the 12V or 5V signal.
The rise and fall times won't be perfect, but they'll be pretty good considering the low frequency.
The power supply should be around 14 or 15 volts (16V absolute max) to ensure a good 12V output.
