Astable 555 circuit with a period of up to 10mins

Thread Starter

JulesP

Joined Dec 7, 2018
89
Hi there,

I would like some help designing a 555 timer astable circuit that has a flip time of up to 5 mins (Period 10mins) and a mark to space ratio of exactly 50%. I have built three versions based on circuits from contacts and websites and they all are not quite right when it comes to measuring the parameters.

I have shown the three I have used so far in the three attached graphics. No 1 I could not get to work at all, No 2 can give me a good 120s period but the two states were not of equal duration and out by about 7 secs over that time. No 3 similarly can give me the long periods but is again not equal.

The circuit is used to switch between two banks of batteries so that they have equal discharge and charging times. Is there another circuit variation that will provide a period of 120-600s and equal durations of high and low?

I appreciate any thoughts,

Jules
Option 1.jpeg
Option 2.jpeg
Option 3.jpeg
 

AlbertHall

Joined Jun 4, 2014
8,187
You are really pushing the envelope trying to get accurate long periods from a '555.
You don't say which flavour '555 you are using. You would stand a better chance with a CMOS version (LMC555, TS555...).
Schematic 3 is the way to go.
 

Thread Starter

JulesP

Joined Dec 7, 2018
89
Thanks Albert.

It's a SE555P from Texas Instruments. Is that not a suitable one?

Jules
 

AlbertHall

Joined Jun 4, 2014
8,187
The SE555 is not CMOS. The CMOS types have lower leakage so you can use higher value resistors and lower value capacitors. Electrolytic capacitors are also leaky - you might consider using a tantalum for the timing capacitor for lower leakage.
 

danadak

Joined Mar 10, 2018
3,507
What is accuracy spec you want for period of timer ? 1%, .1%......?

Regards, Dana.
 

Thread Starter

JulesP

Joined Dec 7, 2018
89
Hi Dana,

The period can be 1-3% but the mark to space ratio preferably <1%.

Jules
 

AlbertHall

Joined Jun 4, 2014
8,187
For accurate 50% mark/space you might be better off using the 555 to trigger a D-type flip-flop IC such as a CD4013, or a counter IC.
Indeed and this will also halve the required '555 period making that easier too.
 

Thread Starter

JulesP

Joined Dec 7, 2018
89
Alec, I'm not familiar with that option. Does the 555 still use the same components for the period i.e in my case 1000uf and 100-200k? Or does the flip flop IC contain or use external components to determine the period and is just triggered by 555 pin 3? Would you be able to send a sketch circuit?

Thanks

Jules
 

danadak

Joined Mar 10, 2018
3,507
This will do the job. Board costs $4. Only external component is a cap for
power supply pin and the pot to adjust freq out. Using another pin for a jump-
er could disable the pot for a fixed 600 sec.

Takes ~ 8 lines of code. 50% is exact, timing (period) is +/- 2%, but thats over a
T range of 40 °C to +105 °C .

upload_2018-12-8_8-24-9.png


http://www.cypress.com/documentation/development-kitsboards/psoc-4-cy8ckit-049-4xxx-prototyping-kits

Board shown below not actual size.




Same thing can be done with ATTINY85, 8 pin dip, programmed
in basic language. Did not look up timing accuracy.

Regards, Dana.
 
Last edited:

eetech00

Joined Jun 8, 2013
1,626
Hi

Use a CD4060B, its better suited for accurate long time periods and already has the internal digital components to provide an output at 50% duty cycle.

eT
 

danadak

Joined Mar 10, 2018
3,507
CD4060B timing accuracy, not including accuracy of Cap, is
+/- 10%......

Maybe not a good choice.


Regards, Dana.
 

Thread Starter

JulesP

Joined Dec 7, 2018
89
I'm not clear which of the items shown on the 'TopDesign.cysch are on the purchasable board. Is the PWM and the ADC-SAR_Seq_1 on this board?

Is Clock_1 from the 555 setup to deliver 100Hz? And on the PWM what is 'tc' and where does the Reset come from? Which component is the CD4060?

Sorry but electronics is not my primary skill.

Jules
 

eetech00

Joined Jun 8, 2013
1,626
I'm not clear which of the items shown on the 'TopDesign.cysch are on the purchasable board. Is the PWM and the ADC-SAR_Seq_1 on this board?

Is Clock_1 from the 555 setup to deliver 100Hz? And on the PWM what is 'tc' and where does the Reset come from? Which component is the CD4060?

Sorry but electronics is not my primary skill.

Jules
The CD4060B is counter that has a built in, adjustable oscillator, and multiple outputs.
Each output produces a time delay based on the oscillator frequency. The oscillator can be RC based, or for more accurate time, a crystal can be used.

eT
 

bertus

Joined Apr 5, 2008
19,944
Hello,

I would agree with that.
The timing accuracy will depend on the quality of the capacitor.
When the capacitor is temperature dependend, the timing will change with the temperature.

Bertus
 

Alec_t

Joined Sep 17, 2013
10,267
Would you be able to send a sketch circuit?
Here you go. In view of the above comments the internal clock oscillator of the 4060 is not used here. Period timing accuracy is dependent on the 555 and C2. Mark/space ratio is set accurately by the binary counter IC. Note the timing cap no longer needs to be an electrolytic. You could make R1 a 500k pot if you want timing adjustment.
10minTimer.PNG
 

MrChips

Joined Oct 2, 2009
19,158
There is more than one way to skin this cat.

If you must use a 555-timer, use a CMOS version such as LMC555 or TLC555. Do not use an electrolytic capacitor which means your capacitance has to be less than 10μF. Use a multi-stage counter such as CD4020, CD4040 or CD4060. This will guarantee 50% duty cycle output.

You can also use the CD4060 directly with a simple RC oscillator and this should work well.
If you want very stable timing, use a quartz crystal to give you better than 10 ppm accuracy.
You can use a 32768Hz crystal on a CD4060 followed by a second multistage counter to give you long time periods.

If you are in microcontroller programming, the simplest single chip solution is to use a low power MCU with a 32768Hz crystal. Such a solution will run on a button battery for years. I have a blog to show you exactly how to do this using an MSP430 MCU.
 
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