if you look at how the standard circuit works, you will see that, whilst
it discharges the timing capacitor through a single resistor, it charges
it through that resistor plus a further one. Hence the time to charge is
greater than the time to discharge.
Just alter the circuit so that it charges and discharges through the
same total resistance. Hint: This will require an additional resistor.
However, if you want an accurate 50% duty cycle, you really need to add
a divide by two to the output.
There are different ways to do it:
. Connect the charging resistor not to Vcc but to the output
. Use diodes to have different paths for charging and discharging
The circuits are available on the Net. Just google for it.
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