# Modify a frequency?

#### Nisse33

Joined Feb 26, 2021
10
Hi,
Keep in mind that I've just started my journey in electronics, so feel free to correct my errors!

I'm looking for a function to power a motor as follows:
Each ≈ 48hour i want to power my 9v motor for x seconds aiming for x=10-20.
The circuit is powered by 9V and needs to consume as low current as possible..
I have made an schematic at the bottom
I have found the CD4521b flip-flop gives me the time interval of approx 48h
If I'm right the flip-flop will give me an 9v output 24h/on 24h/off 24h/on.....?

But the thing is that i only want it to be on for ~10-20 seconds and then off for (48h - (10-20sec))

I have found that I could use an 555 Cmos timer to make an delay for 10-20 seconds but if I understand right it activates by an pulse.
The problem is that i get constant voltage for ~ 24h from my flip-flop.. Is There any way i can cut the positive frequency after just 2 seconds to make an pulse that can give the signal to the 555 timer?

voltage y
time x
A=2 seconds
B= 48h - 2seconds

Thanks for the help
//Nisse

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#### LesJones

Joined Jan 8, 2017
4,106
I don't see how you can get one pules every 40 hours from a CD4521B with a 32.768 Khz crystal. Q 21 will give 1 pulse every 8 seconds so you would then need to divide this by 21600 to get one pules every 48 hours. When you get 1 pulse every 48 hours every 48 hours you would then pass it through s differentiator (A capacitor and resistor.) to trigger your 555.
Have you considered using a micro controller as this would reduce the component count ?

Les.

#### Alec_t

Joined Sep 17, 2013
14,005
Welcome to AAC!
Are you aware TI now lists the CD4521 as obsolete?

#### Imre Norbert

Joined Feb 24, 2021
24
Yes you can cut the 10/20 sec delay to whatever you want using a simple RC timer that activates a transistor. You can calculate the resistor capacitor delay by t=R*C. If you want to redesign this using only 555 timers I suggest you use more that one, because at 48 hours you will get poor accuracy. You can find 556 ic-s that have two 555 ic-s inside.

#### BobTPH

Joined Jun 5, 2013
8,092
1 8 pin microcontroller, 3 capacitors, 1 watch crystal, about 20 lines of code.

Bob

#### Nisse33

Joined Feb 26, 2021
10
I don't see how you can get one pules every 40 hours from a CD4521B with a 32.768 Khz crystal. Q 21 will give 1 pulse every 8 seconds so you would then need to divide this by 21600 to get one pules every 48 hours.
Have you considered using a micro controller as this would reduce the component count ?
Thanks a lot for the answer.
I must have gotten the numbers wrong...
Seems like it's quite complicated doing this the ''Analog'' way
I may consider using an microcontroller instead.. I will look it up.

If I understand what you have written right.
if I find a way to get the right frequency, I can use caps and resistors as an filter to give the timer the signal it needs.
but it wont be as accurate as an microcontroller

Thanks for your understanding that this is new to me!

#### Nisse33

Joined Feb 26, 2021
10
1 8 pin microcontroller, 3 capacitors, 1 watch crystal, about 20 lines of code.
Seems like the easiest way to go is using an microcontroller, Will for sure look it up!
If I can't find a more ''analog'' way doing it. this might be the way.

I kinda like too keep computer coding out of this so i can learn by using basic components.
That's why I'm so stubborn not using an mc.

Thank you so much!

#### LesJones

Joined Jan 8, 2017
4,106
Here is a suggested division scheme. Use Q23 output. This has a period of 256 seconds. This need to be divided by 675 to get 48 hours. Use two divide by 5 counters. (Some decade counters can be used to divide by 5) The first one divides 675 by 5 to give 135. You then divide by 5 again which results with 27. To divide by 27 use a 5 stage counter which would normally divide by 32 but decode a count of 27 and use it to reset this counter to zero. this reset pulse could also be used to trigger your 555 for generating the 10 to 20 second pulse. There are many different ways that you could implement this division sequence.

Les.

#### BobTPH

Joined Jun 5, 2013
8,092
If you don’t have any experience with microcontrollers, maybe an Arduino would be best, though it is overkill fot this use.

Bob