# 555 astable unsual wired

#### ikuus111

Joined Dec 17, 2021
28

Hello, so I found this circuit and it should output square waveform as in astable type.
Does anybody know if this design works the same or different? input is 12v

#### ericgibbs

Joined Jan 29, 2010
15,549
hi,
Astable as the current version, but enables variation in Frequency and Mark/Space ratio [within limits]
E

#### ikuus111

Joined Dec 17, 2021
28
hi,
Astable as the current version, but enables variation in Frequency and Mark/Space ratio [within limits]
E
ok, can you tell me which pin to connect the input of each resistor? I want to use variable resistors

#### ericgibbs

Joined Jan 29, 2010
15,549
hi,
E

#### ikuus111

Joined Dec 17, 2021
28
that means output pin b is wired on the wire of c to pin 7?

#### Alec_t

Joined Sep 17, 2013
12,824
Yes.

#### ericgibbs

Joined Jan 29, 2010
15,549
Hi,
Look at this.
E

#### ikuus111

Joined Dec 17, 2021
28
so b can be wired to either a or c? can use either a or c as input?

#### ericgibbs

Joined Jan 29, 2010
15,549
hi,
A pot has two Outer tags which are connected to the end of the pots resistor, the Wiper of the pot is the Centre tag on the pot.

Post a photo of your pot,

E

#### ikuus111

Joined Dec 17, 2021
28

#### dl324

Joined Mar 30, 2015
14,490
so I found this circuit
I'd advise you to avoid using work from anyone who draws schematics like that. They used connection dots, albeit inconsistently, and wire breaks... You never use both in the same schematic because one negates the need for the other.

At least the symbol they used is half way decent, but pin function should have been in the symbol and pin numbers on the outside.

#### ikuus111

Joined Dec 17, 2021
28
so how do I wire the resistors? in 2nd image you wired b to a, instead of c .
I wire either a or c to pin 7?with b? I red any a or b can be input/ground
Also is there a calculator online for this astable variation to show frequncy? or formula?

#### ericgibbs

Joined Jan 29, 2010
15,549

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#### ikuus111

Joined Dec 17, 2021
28
ok but that calculator is for usual astable? I didnt understand what is the differencem between them? you can change frequncy mark/space ratio with a usual astable

#### ericgibbs

Joined Jan 29, 2010
15,549
hi,
Astable [ which you have built] means it runs continously, Monostable once when triggered.
E

can change frequncy mark/space ratio with a usual astable
Yes

#### ikuus111

Joined Dec 17, 2021
28
sorry. I didnt understand what you said.
What is the diffrence between the 2 astable circuits?

#### crutschow

Joined Mar 14, 2008
29,837
ok but that calculator is for usual astable? I didnt understand what is the differencem between them? you can change frequncy mark/space ratio with a usual astable
The circuit with the diodes allows adjustment of the mark/space ratio from nearly zero to 100%.
The normal astable has a limited range of adjustment.

#### ikuus111

Joined Dec 17, 2021
28
aaa ok ty

#### ikuus111

Joined Dec 17, 2021
28

So I built that circuit on a breadboard. But first I built it with resistors to pretest it. The LED flashed but at a lower frequncy than the 555 for normal astable circuit shown- the flash rate was about 1hz but the calculator has calculated 35 or 80 hz- depending of how I wired the resistors. with values of C1 1uf, R1 10k R2 820 but I considered it worked. than I replaced the resistors with potentiometers. I wired the output/wiper and input everyway( As I have red that you use only 2 pins of pots when used as var res. and all 3 when used a voltage dividers). It only flashed once when I connected the power supply and if I remove the pin 1 to ground wire it stays on.
In another thread some1 said that I have to wire the wiper in the wire of either ground/input to pin. I did and still didn't flash.

Did anyone had a similar problem?

#### DickCappels

Joined Aug 21, 2008
8,714
What is the exact part number of the '555 you are using?