Hello. I am new to the forum and to the actual building of electronics itself. I am trying to put together a timer which will be off for 8 hours and on for 29 seconds. Odd i know. I have pretty much figured out the design i think and the calculations for the resistors and capacitors to give me my desired time. My question at this time before I buy my materials is that I read that electrolytic capacitors values are not entirely accurate and in an 8 hour span it could increase the time by as much as 1 or so hours. Is there another type of capacitor that could be used to more accurately reach my goal? Thank you for your help.

 

Hello,

Do you have a schematic of the circuit upto now?

If you want more stability take a look at crystal oscillators.
The frequency will be higher, but with the correct divider it will work.
You can salvage a 32678 Hz crystal from an old digital watch.

Greetings,
Bertus

 

Yes I do have a diagram i drew up in ms paint. It was based off of a schematics set I found on the net which had some preset values for some resistors and capacitors which I'm not sure of so I left them in. As for the 4060b, 555 timer and relay I have looked around the net at electronics component sites to find them and inputted the model numbers in my drawing which actually took quite a while might I add. Like I said I am quite new to this and did read a little about the crystal but passed it over as it seemed more difficult. A push in the right direction would be much appreciated as I am NOT looking to have all the work done for me. Just a few tips and hints. Thank you.

 

I dont know if its ok to post links to other sites but I got the bulk of my information for the design from here: www.reuk.co.uk/Repeat-Timer-Circuit.htm and then had to search the net for a day or two to figure out the most precise way to calculate for the resistors and capacitors to get my time as that site didn't explain it well enough.

 

Hello,

With the 32678 Hz crystal you can make a "time base" of 1 second.
(dividing the 32768 hz by 32768 = 1 hz = 1 second)
When you make a counter that counts 8 X 60 X 60 , you will have your 8 hours.
The output can trigger a second counter that counts 59 seconds.

Must the 59 seconds be inside or outside the 8 hours?

Greetings,
Bertus

 

The 4060 will take it down to 2Hz, then additional logic would be needed.

I am a fan of the 555. It would make a good test signal, but a lousy time base.

I'm working on a new section of my blog you might like. Basically a cookbook section, and since I know 555 best that is where I'm starting.

Bill's Index

Cookbook Entries

 

The way I understood this to work is that the 4060b with the settings of the cap and res will be on approx 8 hours and then off approx 8 hours. Every time it comes on it shoots a signal to the 555 which then lets the relay trigger for 29secs using the cap and res calculated for it. Which now that I am writing it that way it probably needs to be set at 4 hours on 4 hours off which would give me my 8 hours. Still don' quite understand the crystal setup and Mr. Bill stated something about it then needing additional logic which loses me even more. Sorry if I am taking something simple and turning it into something hard.

 

The 4060 has a built in oscillator, call it a timer. It can be a simple RC oscillator or a crystal time base. The crystal of choice is a 32.676Khz crystal, which is also used in many digital watches. The 4060 also has a 14 stage ripple counter. 2^14 is 16384, or a counter that has 14 bits. This will divide a 32.676Khz signal to 2 hz. All of this is in one chip.

I'm assuming you know about flip flops, which may not be true.

 

I'm sorry but my knowledge is very limited at best to the project and parts I have been trying to set up. I do not know about flip flops other than they are a sort of shoe I do somewhat understand the crystal to the 4060 relation as far as it equals out to about 2.33hz per bit if I am understanding it correctly which I may not. But I do not understand how the crystal is in the chip per your statement "in one chip" nor do I know how I would go about configuring it. Again I'm sorry for my lack of knowledge but would be more than happy to read as much as possible, as not to waste your time, to achieve the knowledge to do this project in the best way possible if pointed in that direction. It is just unsure to me what direction that is now .

 

You will find this site very helpful, everyone starts somewhere.

I reread your original post. Can you read schematics?

What folks are saying is a clock using an RC source isn't that accurate. They drift all over the place.

A crystal is what is used in a digital clock. They can drift too, but are much more accurate.

To start off you want a simple RC circuit though, and build from there.

 

As far as reading schematics I can work my way through them using the internet to figure the symbols accept for the schematics on the relay I previously chose. I have no clue how to hook up to that thing. So if I was to start searching for a new plan for my design you are saying I would design it around all three (4060, 555, and crystal)? Once I can see what I am trying to implement into the design i may have a better idea on searching for how it works and how it can be designed. I do thank you so much for all of your help thus far.

 

I would say go with your other plan if you're comfortable with it. It will be a learning experience. It will drift though. I'm gone for the rest of the day, but I'll be back.

Have you any experience with breadboards?

Take a look at my 555 projects to see what I mean.

The 555 Projects

They are meant for beginners, with lots of show and tell.

 

Have you looked at the ZN1034 precision timer chip? See: http://homepage.ntlworld.com/g.knott/elect439.htm

It's as easy to use as the 555 but can give delays up to several weeks if necessary with normal value components for the R and C.

The output after 8 hours can be used to trigger a 555 for the 29 seconds you require.

The ZN1034 also provides a high and a low output on pins 2 & 3 simultaneously which can be very useful in some circuits.

 

Thyristor, I looked at the link you gave and researched implementing it into my design in place of the 4060 but on the link you gave the timing values they give as examples make no mathematical sense. They don't equal out right. t=0.1 using the five minute values, t=1.2 for the 1 hour values which is correct but then when you go to 24 hours t=33 but should equal 28.8 according to the previous data given seeing that there are (288) 5 minute segments in 24 hours. So how would I go about getting my time of 8 hours when the given information makes no sense? Thank you.

 

Thyristor, I looked at the link you gave and researched implementing it into my design in place of the 4060 but on the link you gave the timing values they give as examples make no mathematical sense. They don't equal out right. t=0.1 using the five minute values, t=1.2 for the 1 hour values which is correct but then when you go to 24 hours t=33 but should equal 28.8 according to the previous data given seeing that there are (288) 5 minute segments in 24 hours. So how would I go about getting my time of 8 hours when the given information makes no sense? Thank you.

The reason they "don't equal out right" is because the author of that article (sensibly) used "Nearest Preferred Values" for components. So he used, for example, a 1uF capacitor rather than the strictly correct 1.2uF capacitor to get an hour. Have you tried to buy a 1.2uF capacitor?

Had you read the article thoroughly, you would have noticed, a few lines down, that he further stated, "The timing period can be adjusted to a more precise value by a trimming potentiometer between pins 13 and 14"

You need to start thinking like an engineer; if the values don't seem correct, then try to work out why that might be first rather than dismissing the article as "making no mathematical sense".

I should also suggest you download the actual ZN1034 data sheet as well to understand fully this neat device.

 

I've done quite a bit more research on the crystal idea Bertus and Bill gave and have come up with and understand that a 32,768 crystal will give my 4060 a signal every 1/2 second being it will be 2hz at pin3 (Q14). How do I get that signal to only give at my 8hr mark (on 4hrs off 4hrs)? I have attached a picture of a diagram using a 4060 and the 32,768 crystal that I found on the internet that I can implement into my design.

 

I apologize Thyristor, as I did read the page thoroughly twice but thought the adjustment meant a finer tuning to the given values that were used as examples. And by no means was I dismissing the article. I was more or less asking how to come up with the more correct answer. Again, I apologize as I am not an engineer . Merely just trying to learn and come up with the best solution for my project as this is a first of hopefully many.

Oh, and don't know what you are getting at with the buying of a 1.2uf cap but from what quick search i did they range from $0.38 - $9.00. Not being a smarty; I just was not sure where you were going with that comment

 

A microcontroller would be your best option for the job. A crystall oscillator can provide an excellent accuracy.....

 

Imartinez, could you point me in a direction for some information on setting something up for my project using a microcontroller? What little I did see on it, I couldn't seem to find how to set it for what I am looking for so I dismissed it and went with the counter/timer setup.

 

Before I may direct you to beneficial information, what is your proficiency within electronics and microcontrollers? Please advise....