Take a look at the CSS555 timer http://www.customsiliconsolutions.com/downloads/Revised Standard products/CSS555_Spec.pdf , available from Jameco. It will likely require the "programmer", but can remove the yucky long-term timer interval performance of a real 555.

www.picaxe.com (processor) might be simple enough for you to use. 0-100% (potentiometer with a voltage reference) can easily be based on an A/D converter.

 

You can actually plug "=1 / 2.2 * 1e6 * 100e-6" into the google search box.
1e6 is 1 meg ohm
100e-6 is 100 uF

as an example

 

i get in reallity 14.99 minutes, not the suposed 32min. Any ideas?

Don't forget the Q14 output of the 4020 goes high half way through its oscillation period, so if you are resetting it at that point (rather than letting it cycle continuously) your timing interval would be half what you expect.

 

You can actually plug "=1 / 2.2 * 1e6 * 100e-6" into the google search box.
1e6 is 1 meg ohm
100e-6 is 100 uF

@Vicente Pchara. If you do this, don't forget to include parenthesis. 1/(2.2 * 1e6 * 100e-6) will give the correct calculation.

 

My set-up now is 0.43u C and a 1.06M R. With this setup i should have 8.3Hz -by the above math- and this frequency divided by 16384 is around 32minutes.

Istead i´m getting 15minutes (actually 14.99).

Using f = 1/(2.4RC), I get 0.9Hz; not 8.3Hz. You could almost do this calculation in your head. M and μ multipliers cancel, 2.4*0.43 is about 1 so f≈1Hz.

 

Hello, i have being working in a design to create a repeating timer with variable time for my aquarium. What i want is an analog timer where i can set a different time spam on T1 and a locked T2. The times can vary from 0-180sec for T1 and 15-30Min to T2.
I want to implement a model of aquaponic´s filtering system in my aquarium to manage some experiments with flow and dirt removal/clogging.

My design so far is based in 3 Cmos: 4020, 4093, 555.
I thought to use a 4093 as a Monostrable timer for T1. 555 for a multivrator to generate a pulse for 4020 which will set T2. In this scenario the Monostable timer can be adjusted with the help of a potentiometer to set T1 independently of T2. One future idea is to change 4020 with 4060 so I could get rid of 555. The problem I am facing with this is that my monostable timer first set does not fully charge the capacitor, so only in the second cycle the T1 timer actually have a steady timing. Also, I am not sure why but in my Proteus simulation the state of my 3rd Nand gate gets grey, leading to a indefinite state in 4020 reset and the start of counting before the end of T1, this occurs only in first cycle.

This can be set very easily with a microcontroller, but for sake of parts and knowledge i want to try to make this with analog. Also, managing analog real-time time set with microcontroller can be tricky with potentiometer, which would lead to a complex case of HMI.

Yes, i have seen thehttp://www.zen22142.zen.co.uk/schematics, but believe me, the ones that could work for me just did not work in my proto board. I am not sure why. For instance,http://www.zen22142.zen.co.uk/ronj/rt7.html, could have made this very simple, but i tried with 4093 and could not make it to work no matter how hard i tried. Also i could not simulate this in Proteus, maybe because the capacitance limit of Proteus.

If you have any ideas on design or directions I would thank you from the bottom of my heart. Seriously, I have spent too much time in this project so far, and it became personal, haha.

How accurate do the timers have to be?

 

Hi, thanks for all the replies. I really apreciate!

Using f = 1/(2.4RC), I get 0.9Hz; not 8.3Hz. You could almost do this calculation in your head. M and μ multipliers cancel, 2.4*0.43 is about 1 so f≈1Hz.

Yes and no, dl324. Are you sure? I have made this on excell and checked the corretcness of the values double time. With a 2.2 constant i get 9Hz, not 0.9Hz. Well i´m trying the whole formula that you posted:

As i have learned i need to deduct the time filling of the capacitor and the time it takes to emptying it. This is hard to do for me as i´m a hobbyst. But lets see.

With a 12V supply with 1.06M (1060000) R and a 0.473uF (4,73E-08) C the I (amp) will be 1,13208E-05 so it will take C/I= 0,00417817 seconds to fill it. Right?

41% duty cycle? I think i´m missing something here.

That´s how far i got.

Take a look at the CSS555 timer http://www.customsiliconsolutions.com/downloads/Revised Standard products/CSS555_Spec.pdf , available from Jameco. It will likely require the "programmer", but can remove the yucky long-term timer interval performance of a real 555.

www.picaxe.com (processor) might be simple enough for you to use. 0-100% (potentiometer with a voltage reference) can easily be based on an A/D converter.

Hi, thanks for the idea. But i´m avoiding to include another IC on the design. My design is ready: two 4060, one control ON time and other OFF time. First is variable and second is fixed. It´s also repeating timer. And yes i made one arduino based, it was very simples but as i started to make is more complex i got stuck on the coding (precise timing/wanna add LCD/need for a RTC) also everything starts to get little frail in assembly.

 

Don't forget the Q14 output of the 4020 goes high half way through its oscillation period, so if you are resetting it at that point (rather than letting it cycle continuously) your timing interval would be half what you expect.

Hi, I’m thinking about it, maybe that´s it. This happens because the counter have to be like 111111111 instead of 100000000 to reach it´s max counter?

Thanks.

 

This happens because the counter have to be like 111111111 instead of 100000000 to reach it´s max counter?

Correct.

 

How accurate do the timers have to be?

Hi Fields, the problem is repeatability. I´m working with water pumps in small displacement of fluid in each cycle so the precision is also related to a repeatability of cycles. That’s why I’m working with 15minutes OFF = 1/4 of hour. And the ON time have to be precise in terms of setting. The optimum solution would be a MMI with analogical input of variables with a PIC/Atmega and a RTC. But that´s not my deal right now. I´m working with Cmos and also enjoying the learning curve.

I got my idea from http://www.homemade-circuits.com/2012/04/how-to-make-simple-programmable-timer.html

 

Correct.

Wow, in this case i will try some other tests and come back to assure if the formula ir right

Thanks a lot.

 

Putting all of that rhetorical face saving nonsense aside, as well as where you've been, blah blah, and what you've done, blah blah, how accurate do you need the timers to be?

 

Are you sure?

Yes.
\( \small f=\frac{1}{2.4RC}=\frac{1}{2.4*1.06e6*0.43e-6}=\frac{1}{2.4*0.458}=\frac{1}{1.09392}=0.914Hz\)

I have made this on excell and checked the corretcness of the values double time.

I entered in excel also and it's giving me answers I believe.

 

0.473uF (4,73E-08)

No. 0.473u = 4.73e-07

 

Yes.
\( \small f=\frac{1}{2.4RC}=\frac{1}{2.4*1.06e6*0.43e-6}=\frac{1}{2.4*0.458}=\frac{1}{1.09392}=0.914Hz\)
I entered in excel also and it's giving me answers I believe.

But the 0.473uF = 4.73×10-7 F

My cap is 473K (pF) so 0.473uF

or i´m reading it wrong?

 

Putting all of that rhetorical nonsense aside, how accurate do you need the timers to be?

1-2 Seconds variations.

nonsense?

 

But the 0.473uF = 4.73×10-7 F

My cap is 473K (pF) so 0.473uF

or i´m reading it wrong?

Read your post in #12.

My set-up now is 0.43u C and a 1.06M R. With this setup i should have 8.3Hz

You are reading the capacitor value incorrectly and you're making typo's that you aren't catching when you proofread your posts. 473 means 47000pF which is the same as 0.047uF.

I understand that you're a hobbyist, but you need to be more careful so we don't waste time.

 

The 'K' in the cap value indicates 10% tolerance.

 

Well, thanks for the information.

Dennis, that doesn't make you right as this was the first time i showed the value ON the cap instead of my idea of the value.
0.47uF is 4.73×10-7.

Everybody makes mistakes. Sorry if i made you loose your time.

For me that´s how people learn stuff, making mistakes. You can only be more careful if you know what needs to treated more carefully.

I will be extra careful about reading components from now on (more than i´m already am).

Also, scientific notations can be tricky when you don´t do them everyday, as i don´t.

 

My cap is 473K (pF) so 0.473uF

so, just use 47000E-12; that's 47 followed by 3 zeros and E-12 for pf or re-written
47000E-12
or
047 000 E-12
or
047 e-9
or
0.047 e-6
or
0.047 uF

A calculator with engineering notation is much better. Exponents in multiples of 3.

Here, i just showed you howto convert easily without any math , really.

PS: The CSS555 basically includes the counter chips