Help about 555 timer

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pop6335 said:
How to build 20 minute on , 20 minute off by single 555 timer
Click to expand...

You don't, it's far too long a delay for a 555 - simplest option is to use a PIC, or CMOS counters from a crystal oscillator. But a single 8 pin PIC will do the job much more easily.
 
Sorry you mean use microcontroller ? , but my project is not using micro controller . is out of the budget.

By the way is we can controller by using the resistor value and cap value ?
 
Last edited:
pop6335 said:
Sorry you mean use microcontroller ? , but my project is not using micro controller . is out of the budget.

By the way is we can controller by using the resistor value and cap value ?
Click to expand...
A 555 costs 18p or thereabouts and a 16F629 costs 90p as an example. Is your budget really that tight?

David.
 
pop6335 said:
Sorry you mean use microcontroller ? , but my project is not using micro controller . is out of the budget.

By the way is we can controller by using the resistor value and cap value ?
Click to expand...

But NOT for 20 minutes!!.
 
Actually the simplest option would be to use the longest stable 555 timer circuit you can find and simply feed the output into a ripple counter IC. Every successive stage will double the effective output'd time. Though since the 555 isn't exactly a precise device you're going to get a lot of variation. If you need 20 minutes exactly (or close to exactly) a micro controller (PIC or AVR) would suit well.
 
Are you sure micro controllers are out of your budget range? I checked the prices at Digi-key. A generic NE555 timer goes for about 45 cents. An AVR tiny11 micro controller sells for 55 cents.
 
A CMOS IC like the CD4060 probably costs less than a 555 and easier to use than a PIC if you don't have a programmer.
 
Digi-key lists the CD4060 at about 48 cents, and that's a 16pin package. And you have to have the counter AND a clock source to create a timer, so you'd still need a 555. The AVR tiny's or a comparable pics are so versatile and cheap just about anyone using electronics should be able to use something of their sophistication, simple programmers are easily hand built using a few passive components, maybe a transistor or two on a breadboard. Development software is free and source code is readily available. In bulk they're only about 38 cents. You can't even get a candybar for that nowdays =>
 
The CD4060 has an on chip oscillator so you don't need a 555, all that's required is a couple of resistors and a capacitor - the same number of componants as an astable 555.

See the datasheet.
https://www.fairchildsemi.com/ds/CD/CD4060BC.pdf

The only question is accuracy, if you want precision then add a separate crystal oscillator and divider or if you have a programmer it's cheaper to use a PIC.
 

Is there any sample circuit to refer for using a ripple counter?
 
It's easiest to just buy a ripple counter IC. But you can create one using D-type flip flops. Tie the !Q line of a D-type flip flop to it's data line and strobe the clock line. On every leading edge of the clock line you will get a state change on the Q line, it effectivly halves the clock rate. If you tie the Q line of one flip flop to the clock line of the next flip flop it divides again... and again... as many times as you want, but always by two. Ripple counters have this all neat and tidy built into a single IC.
 
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