# 555 timer circuits.

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#### Sonny120

Joined Nov 5, 2023
13
Good night.
I am having trouble creating 555 timer circuits which will give the following outputs.

What I was trying to do is create 2 50% duty cycle signals. The peak is 5 V and 0 V at the bottom. With Signal B being phase shifted by 90° from phase A. While C is the 2 signals being AND'ed. D is both signal being OR'ed.

My main problem is I'm not sure how to go about making the 2 50% duty cycle circuits for A and B. The frequency of the circuit is supposed to be 200 Hz. Is there a simple way to do this?

#### eetech00

Joined Jun 8, 2013
3,823
Hi

Assuming your wave forms are correct, signal D should be a NOR of A and B.

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#### crutschow

Joined Mar 14, 2008
34,047
As noted by eetech00, waveform D is not the OR'd signal, it is the NOR'd signal.

My take on a circuit, which is as simple as I can make it (below):
The 555 is adjusted to give a 800Hz frequency for 200Hz FF outputs.
The 555 output does not need a 50% duty-cycle since both FF's are triggered on the rising clock edge, which gives an exact 50% FF output duty-cycle and 90° phase-shift, independent of the 555 duty-cycle.

The "C" AND signal is generated by the inverted FF signals connected to a NOR gate.

Note: Tie all unused CD4001 inputs to ground.

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#### Ian0

Joined Aug 7, 2020
9,503
What's the point of Q1, D1, D2 and R2.
You could do it more simply by using the 555 to clock a 4017 and taking Q0 and Q2, with reset connected to Q4.

#### Sonny120

Joined Nov 5, 2023
13
Thank you guys for all the responses It was a NOR gate that I meant sorry for the mistake These circuits seem very reasonable.

#### Sonny120

Joined Nov 5, 2023
13
What's the point of Q1, D1, D2 and R2.
You could do it more simply by using the 555 to clock a 4017 and taking Q0 and Q2, with reset connected to Q4.
By this you mean create the 200Hz clock then use a 4017? Also by Q0 and Q2 do you mean the first clock in that quarter?

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#### Ian0

Joined Aug 7, 2020
9,503

#### eetech00

Joined Jun 8, 2013
3,823
What's the point of Q1, D1, D2 and R2.
You could do it more simply by using the 555 to clock a 4017 and taking Q0 and Q2, with reset connected to Q4.
maintains 50% duty cycle independent of frequency.

#### Ian0

Joined Aug 7, 2020
9,503
maintains 50% duty cycle independent of frequency.
Neat.
I'd just use a resistor from pin 3 to pins 2/6 to set the frequency.
but I'd be using a CMOS 555.

#### crutschow

Joined Mar 14, 2008
34,047
You could do it more simply by using the 555 to clock a 4017
How does that generate the desired two 90° phase-shifted signals?

#### Ian0

Joined Aug 7, 2020
9,503
How does that generate the desired two 90° phase-shifted signals?
It generates signals C and D. Isn't that what was required?
If you want A and B, then an OR between 0 and 1 gives A, and 1 and 2 gives B.

#### crutschow

Joined Mar 14, 2008
34,047
If you want A and B, then an OR between 0 and 1 gives A, and 1 and 2 gives B.
Still don't see how that gives the 90 degree shift with a CD4017 since only one output is high at a time(?).

#### Ian0

Joined Aug 7, 2020
9,503
Still don't see how that gives the 90 degree shift with a CD4017 since only one output is high at a time(?).
but I can't make it work in SPICE with a diode OR-gate.
Something to do with setting the output current of the logic device. ...

#### ericgibbs

Joined Jan 29, 2010
18,654
Hi Ian,
Please post that last LTS asc file.
E

#### Ian0

Joined Aug 7, 2020
9,503
Hi Ian,
Please post that last LTS asc file.
E
Unfortunately, I didn't save it.

#### eetech00

Joined Jun 8, 2013
3,823
Neat.
I'd just use a resistor from pin 3 to pins 2/6 to set the frequency.
but I'd be using a CMOS 555.
Here's a CMOS TLC555 version.
I don't know how well it holds 50%DC under mfg variances or frequency changes tho...

#### dl324

Joined Mar 30, 2015
16,688
Was this post moved to Homework Help after members started posting circuits?

#### ericgibbs

Joined Jan 29, 2010
18,654
Moved at:

• Today at 8:42 AM
Today at 8:42 AM

Mod.

#### eetech00

Joined Jun 8, 2013
3,823
View attachment 307918but I can't make it work in SPICE with a diode OR-gate.
Something to do with setting the output current of the logic device. ...
Here your circuit using diode OR's

#### Ian0

Joined Aug 7, 2020
9,503
What did you do to the CD4017 model to make it work? Or did yours work straight away and there's something wrong with my 4017 model.
And you don't need the 4001s because the C and D waveforms are on the 0 and 2 pins of the 4017.

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