# 555 TIMER CIRCUIT DESIGN

#### BBGIRL

Joined Jul 27, 2022
5
I am trying to develop the circuit based on the input signal 10ms clock period signal, and the duty cycle I gonna use is 10% or 20%, which indicates if a user presses a button in the remote controller or not. When the duty cycle is 10%, the designed circuit output constant 0V; while when the duty cycle is 20%, the designed circuit generate another 10ms clock period signal with duty cycle 60%. I am thinking of using 555 timer but don't know where to start can someone guide me on this?

#### crutschow

Joined Mar 14, 2008
32,926
Does the output for the 20% duty cycle need to be in sync with the input?

Joined Jul 18, 2013
27,653
Here is one source to start.

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#### BBGIRL

Joined Jul 27, 2022
5
Does the output for the 20% duty cycle need to be in sync with the input?
yes

#### crutschow

Joined Mar 14, 2008
32,926
Here's the LTspice simulation of a 555 circuit that I think does what you want:
Note that the circuit is sensitive to the RC time constants, so some tweaking of C1, and/or R1 and R3 may be required for proper operation, depending upon how close to a 60% output duty-cycle you need.

#### BBGIRL

Joined Jul 27, 2022
5
Here's the LTspice simulation of a 555 circuit that I think does what you want:
Note that the circuit is sensitive to the RC time constants, so some tweaking of C1, and/or R1 and R3 may be required for proper operation, depending upon how close to a 60% output duty-cycle you need.

View attachment 272362
Thanks for the guidance. I tried out the design with LTspice simulation but for some reason, I am getting 5v at the initial stage. And can you explain how did you give the input pulse signals values?

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#### BBGIRL

Joined Jul 27, 2022
5
Here's the LTspice simulation of a 555 circuit that I think does what you want:
Note that the circuit is sensitive to the RC time constants, so some tweaking of C1, and/or R1 and R3 may be required for proper operation, depending upon how close to a 60% output duty-cycle you need.

View attachment 272362
And how did you find the value of Capacitors and Resistors? is there any formula?

#### crutschow

Joined Mar 14, 2008
32,926
And how did you find the value of Capacitors and Resistors? is there any formula?
I have no particular formula, but you could certainly calculate them using the exponential charging equations for RC circuits based upon the known trigger threshold voltages of the 555 (1/3 V+ for Trig and 2/3 V+ for Thrs) along with the signal characteristics, however I just adjusted them in the simulator until the desired output was achieved.

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#### BBGIRL

Joined Jul 27, 2022
5
You could certainly calculate them based upon the known trigger threshold voltages of the 555 (1/3 and 2/3 of V+)
and the signal characteristics, but I just adjusted them in the simulator until the desired output was achieved.
Do you know why my initial output started at 5v even though I followed your design?

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#### crutschow

Joined Mar 14, 2008
32,926
Do you know why my initial output started at 5v even though I followed your design?
Not sure, but you are not using the same 555 model as I used (mine is a transistor-level model, while yours is an idealized).
(Note that your simulation shows an ideal 5V output, whereas mine is about 4.7V).

There is an initial transient that gives an output high, which occurs when circuit power is first applied (would that be a problem?).
The transient is due to the time it takes for the Trig voltage to charge up.
This can be prevented if C1 is connected to V+ instead of common.
Below is a simulation of the modified circuit, without the initial Spice DC bias calculation to show the power-up transient:

#### ci139

Joined Jul 11, 2016
1,874
http://beta-tools.analog.com/timerblox/LTC6993
inputs : Voltage Controlled /// Supply 5 /// Div code 3 /// Pos. Pulse Min.(s) 800u Min. (V) 0 /// Trig. Rising Edge Max (s) 1200u Max (V) 5 /// Non-retriggerting

the button press can be communicated to VC input

Update : it seems i misread the desired function of the circuit

+ a less messy ver.

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#### crutschow

Joined Mar 14, 2008
32,926
the button press can be communicated to VC input
Did you post this in the wrong thread, because it doesn't seem to make sense in this one?