Re: 555 timer question: how to calculate required resistors and capacitor to achieve desired frequency?
- From: Ross Herbert <rherber1@xxxxxxxxxxxxxx>
- Date: Mon, 27 Nov 2006 15:32:02 GMT
On Mon, 27 Nov 2006 02:57:24 GMT, Impmon <impmon@xxxxxxxx> wrote:
I tried Googling but all the formula for finding 555 timer frequency
is based on known capacitor and resistor values to find frequency.
I need to build a monostable timer to get 140Hz. I could throw in a
random capacitor and one resistor but my algebra skill is rusty (no
complex math formula in over 10 years!!)
The system will be running on 5v DC as it contains a few TTL chips.
You sure you aren't wanting an "astable" at 140Hz?
Using the 555 tool at
https://wwws.ee.ucl.ac.uk/facilities/teachlab/inter
You will still need to "select" a component to start with. Cap Ct is
easiest and experience suggests that for 140Hz a good starting value
is 470nF. Plug in the supply voltage and then experiment with Ra and
Rb values making sure they are equal if you want 50:50 duty cycle.
Just so you get a bit of practice start of with Ra = Rb = 8.2K and go
from there....
You can select another Ct value and experiment with Ra, Rb again.
.
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