555 timer question...

[Impmon]

I wanted to build an astable timer with variable frequency, duty cycle don't
matter. What I would like is to use variable resistor to obtain frequency
of between 1 Hz and 100 Hz (not exact, just close)

I've tried a few online calculator but with 3 variables, one being variable,
makes computation tricky. The few I've tried doesn't really offer linear
frequency change but rather ramps from low to high in just a touch of
variable resistor knob. I have 100ohms, 10k, and 1 mega variable resistor,
and assortment of fixed from 1 to 100 mega and several common value
capacitors.

TIA for any information that would help me.

 

[David Eather]

Impmon wrote:

I wanted to build an astable timer with variable frequency, duty cycle
don't matter. What I would like is to use variable resistor to obtain
frequency of between 1 Hz and 100 Hz (not exact, just close)

I've tried a few online calculator but with 3 variables, one being
variable, makes computation tricky. The few I've tried doesn't really
offer linear frequency change but rather ramps from low to high in just
a touch of variable resistor knob. I have 100ohms, 10k, and 1 mega
variable resistor, and assortment of fixed from 1 to 100 mega and
several common value capacitors.

TIA for any information that would help me.

Goto:

http://www.fairchildsemi.com/ds/LM/LM555.pdf

set Ra = 1k
set C1 = 1uF
set C2 = .01 - .1uf
for Rb use a 4.7k resistor in series with your 1M pot (wired as a rheostat)

frequency range will be approx. 1 - 100 Hz. The data sheet has all the
details you need to understand this device.

 

[David Eather]

David Eather wrote:

Impmon wrote:
I wanted to build an astable timer with variable frequency, duty cycle
don't matter. What I would like is to use variable resistor to obtain
frequency of between 1 Hz and 100 Hz (not exact, just close)

I've tried a few online calculator but with 3 variables, one being
variable, makes computation tricky. The few I've tried doesn't really
offer linear frequency change but rather ramps from low to high in
just a touch of variable resistor knob. I have 100ohms, 10k, and 1
mega variable resistor, and assortment of fixed from 1 to 100 mega and
several common value capacitors.

TIA for any information that would help me.


Goto:

http://www.fairchildsemi.com/ds/LM/LM555.pdf

set Ra = 1k
set C1 = 1uF
set C2 = .01 - .1uf
for Rb use a 4.7k resistor in series with your 1M pot (wired as a rheostat)

frequency range will be approx. 1 - 100 Hz. The data sheet has all the
details you need to understand this device.

forgot to add that you should be looking at figure 5 on page 5

 

[petrus bitbyter]

"Impmon" <impmon2@tds.net> schreef in bericht
news:_Iq5m.2027$cW.1647@newsreading01.news.tds.net...

I wanted to build an astable timer with variable frequency, duty cycle
don't matter. What I would like is to use variable resistor to obtain
frequency of between 1 Hz and 100 Hz (not exact, just close)

I've tried a few online calculator but with 3 variables, one being
variable, makes computation tricky. The few I've tried doesn't really
offer linear frequency change but rather ramps from low to high in just a
touch of variable resistor knob. I have 100ohms, 10k, and 1 mega variable
resistor, and assortment of fixed from 1 to 100 mega and several common
value capacitors.

TIA for any information that would help me.

First the standard answer: Use a PIC

Using a 555 you can achieve your frequency range in the standard a-stable
configuration using a 0.47uF capacitor, a 470R resistor for R1 (often called
Ra) and a 1M5 pot in series with a 15k resistor for R2 (Rb). However, the
frequency will be highly nonlinear in relation to the turned angle of the
pot.

petrus bitbyter