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Long Delays with the 555 Timer or Alternate IC
JohnInTX

....but not a uC! I am dead-in-the-water with respect to uC's.
The entire project will be a Sequential Float Charger circuit using a single Float charger. I am looking to control the rotation of a half dozen Lead-Acid Batteries. My plan is to use a timer that will produce a charge time of 10, 20, or 40 minutes before switching to the next battery. My current dilemma is getting a somewhat stable time period out of the 555 timer. The circuit below is the general idea.


Not only am I looking for the ON times of 10min, 20minm 40min, but I am looking for the 1sec OFF time to advance the CD4017 to connect the next battery. The times for the 555 are not needing to be super accurate, within a minute or two. So far, though, The times have been inconsistent when using three 220uF Low ESR Caps in parallel. I looked at a 330uF Ceramic cap and almost ____ my pants, $22.

For the 10min Timer, I'd like to stay +/- 30sec, for the 20Min timer maybe +/- 1min, and for the 40min timer, +/- 2min. It really stinks to sit waiting 20/40min to see how close I am. And YES a uC would be great, but I want the project done long before I learn the language well enough to make this happen.

I have a few ICM7242IPA PDIP-8 Timers that would enable me to easily get accurate timing, but the chip does not seem to be able to alter the duty cycle so that I can increment the CD4017. DATASHEET

Help & Suggestions needed!
Thanks ALL!

 

What you need is to count faster and then divide the clock frequency to get the time period you want. There are many ICs used for frequency division. For example an MC14521B.

I chose that particular IC to use in an example. I haven’t personally used it. But for an example to illustrate the concept, it’ll do.

Here is s link to its datasheet.
https://www.onsemi.com/pub/Collateral/MC14521B-D.PDF

Note that at one of its outputs, it will divide the input frequency by 524, 288. This is close to 600,000, which happens to be the count to 10 minutes when using a 100Hz clock.

555 oscillators are more stable at 100Hz than once every 10 minutes.

Pin Q19 will change state every 10 minutes. The clock rate isn’t exactly 100Hz, but I don’t feel like doing the math now. Note that pin Q20 will change states every 20 minutes and subsequently pin 21 will change states every 40 minutes.

The “secret” to this solution is dividing a higher frequency to get the time that you want.

 

Hi

You could use a single CD4060 to provide the different timers but you would have to select the timer output to use to drive the CD4017.
How will you select the time to use? Selector switch?

eT

 

What @eetech00 said..,

 

Have you seen TimerBlox?

Analog Devices TimerBlox parts are small, accurate, and simple timing devices designed for six basic operations: voltage controlled oscillation (VCO), low frequency clocking, pulse-width modulation (PWM), one-shot generation and signal delay, and power-on reset (POR). TimerBlox devices combine an accurate programmable oscillator with precision circuitry and logic. No capacitors, no crystals, no microcontroller, and no programming are required. A 20 mA source and sink capability enables the devices to directly drive opto-isolators and transformers for electrical isolation. An ideal solution for space-limited applications, each TimerBlox device can be placed at the point of use.

https://www.analog.com/en/products/clock-and-timing/timerblox.html
You could use one of the long-period astable ones like the LTC6995 to drive the sequencer.

 

I understand the sequential part, and the part where each sequence has
a particular float period. But how do you want, for each sequence, to change
the period of float ?

And you mention duty cycle, duty cycle of what ?

Regards, Dana.

 

but the chip does not seem to be able to alter the duty cycle so that I can increment the CD4017

You can add a 555 one-shot to give the 1 second time when the ICM7242IPA times out.

 

You can add a 555 one-shot to give the 1 second time when the ICM7242IPA times out.

This needs to repeat continuously...20min/1sec/20min/1sec/20min/1sec...in other words a period on 20min +1sec. Kind of like a duty cycle of 99%. I believe the CD4017 increments on the completion of 1 cycle

Hi

You could use a single CD4060 to provide the different timers but you would have to select the timer output to use to drive the CD4017.
How will you select the time to use? Selector switch?

eT

The selector switch would be either a 3 position toggle or simple dip switches.

 

I understand the sequential part, and the part where each sequence has
a particular float period. But how do you want, for each sequence, to change
the period of float ?

And you mention duty cycle, duty cycle of what ?

Regards, Dana.

The 10min, 20min, 40min float period would be selected prior to beginning the sequence.

Duty Cycle - 20min on, 1sec off.

 

So, in addition to providing the 1 second pause, I’d use the signal to pause and reset counting the selected time (10, 20 or 40 minutes).

 

This needs to repeat continuously...20min/1sec/20min/1sec/20min/1sec...in other words a period on 20min +1sec.

Why do you think you need a 1 second pulse?
Just use the ICM7242IPA counter out signal to clock the CD4017.
The CD4017 triggers on the clock rising edge and doesn't care how long the clock stays high.
See the LTspice simulation below of a CD4017 with a 200s period clock that's high for 100s.

 

Why do you think you need a 1 second pulse?
Just use the ICM7242IPA counter out signal to clock the CD4017.
The CD4017 triggers on the clock rising edge and doesn't care how long the clock stays high.
See the LTspice simulation below of a CD4017 with a 200s period clock that's high for 100s.

View attachment 168244

I don't need a 1 sec low, but it does need to go low then high again to trigger the CD4017...YES?
Perhaps that is whats giving me the brain-mash. I will take out the ICM7242IPA and CD4017 tomorrow and give this a try.

 

Hello,

You could do something like this.
See attached.

The CD4060 produces periods of 10, 20, 40 minutes. A CD4017B is used to select the time period via a momentary pushbutton. U2C, R4, C5 form a trailing edge detector to detect the end of the time period and it clocks a second CD4017B to select and activate each mosfet. When a new time is selected the timer is reset so it starts at the beginning of the time period. The circuit is designed for 12 volts (I missed the 5v supply) but a few RC values can easily be adjusted for 5v supply. The circuit requires five chips. I haven't breadboarded it but it works in simulation.

BTW
I didn't see your comment about a selector switch but the pushbutton circuit could be changed for a selector switch. Also, you show an LED hanging off of each mosfet gate. I don't know the type of LED but the CD4017B can only drive about 4ma reliably (MAX spec is 6ma). Might need to move each of those to the drain of each mosfet or drive them differently.

eT

 

This is a natural for a UP.

You could do it in Bascom Basic using an ATTINY85. Clock accuracy a lot
better that 555 timer.

https://www.mcselec.com/index.php?Itemid=41&id=14&option=com_content&task=view


Or a PSOC, accuracy even better at +/- 2% using internal clock. Use a one shot
PWM, set its period based on input pin(s) state or via serial interface, like USB, SPI,
I2C, One Wire, UART.....I think this can be done with fewer onchip resources used,
just got lazy in approach. Keep in mind this is a one chip solution. Maybe 30 lines
of code max. Note using a 32Khz watch xtal, + 2 caps, external connected to chip
gets you +/- .015% timing accuracy.





I know you wanted to steer clear UP, but parts like PSOC and ATTINY85 are hard to beat in solutions
like yours.

This is a one chip solution, no external timing components, unless you need xtal
precision.


Regards, Dana.

 

Your original schematic shows a bipolar 555. This is a problem with very long periods because its input current is a significant fraction of the charging current. A more stable alternative is a CMOS 555 (LMC555).

Separate from that, I'm a big fan of the CD4060 for long period timing applications. The oscillator section is not as stable as the 555, but that is more than offset by the use of much smaller and more accurate external components; particularly the timing capacitor. Plus, the 4060 delivers a 1-2-4 set of output periods without switching either the resistor or capacitor. This, plus a differentiator connecting it to the 4017, sounds like a solution.

ak

 

Your original schematic shows a bipolar 555. This is a problem with very long periods because its input current is a significant fraction of the charging current. A more stable alternative is a CMOS 555 (LMC555).

Separate from that, I'm a big fan of the CD4060 for long period timing applications. The oscillator section is not as stable as the 555, but that is more than offset by the use of much smaller and more accurate external components; particularly the timing capacitor. Plus, the 4060 delivers a 1-2-4 set of output periods without switching either the resistor or capacitor. This, plus a differentiator connecting it to the 4017, sounds like a solution.

ak

Well there's a term I have not run into yet. "Differentiator."
"There are also electronic differentiators, or electrical differentiating circuits. The Figure shows a differentiator based on an electrical analog. For a time-varying input, if the capacitive reactance XC shown in the schematic diagram is very large compared with the resistance R, the current, and hence output voltage EOUT appearing across R, will lead the phase of the input voltage EIN by almost 90°. Thus the output voltage EOUT is the time derivative of the input voltage EIN, EOUT = dEIN/dt."
Can you explain the need for this?
I have no problem with a LMC555, or TCL555 CMOS version.

 

This is a natural for a UP.

I know you wanted to steer clear UP, but parts like PSOC and ATTINY85 are hard to beat in solutions
like yours.

This is a one chip solution, no external timing components, unless you need xtal
precision.

Regards, Dana.

Thanks Dana. I do realize that a UP was made for this project, and I may jump into that game shortly, but for now I will stick to the parts I have in hand. I may solicit your help on UP apparatus when I am ready though!

 

Hello,

You could do something like this.
See attached.

The CD4060 produces periods of 10, 20, 40 minutes. A CD4017B is used to select the time period via a momentary pushbutton. U2C, R4, C5 form a trailing edge detector to detect the end of the time period and it clocks a second CD4017B to select and activate each mosfet. When a new time is selected the timer is reset so it starts at the beginning of the time period. The circuit is designed for 12 volts (I missed the 5v supply) but a few RC values can easily be adjusted for 5v supply. The circuit requires five chips. I haven't breadboarded it but it works in simulation.

BTW
I didn't see your comment about a selector switch but the push-button circuit could be changed for a selector switch. Also, you show an LED hanging off of each mosfet gate. I don't know the type of LED but the CD4017B can only drive about 4ma reliably (MAX spec is 6ma). Might need to move each of those to the drain of each mosfet or drive them differently.

eT

View attachment 168245

Thanks for the heads-up on the indicator LED's. I was questioning their placement. I do have a few LED's that operate on 2V/2mA and are bright enough for the job, but placing them on the drain of each MOSFET.
As far as the CD4060's are concerned. I do have some in my bag of goods, but may plan to fiddle with the ICM7242 timers first. I appreciate the assistance and may return to it if I run into a snag with the ICM7242 timer method.

Damn, just took care of a foot of snow, with as much as another foot on the way. Think I'll get around to tinker-tronics? Damn straight I will!!

 

I don't need a 1 sec low, but it does need to go low then high again to trigger the CD4017...YES?

Yes.
And a ICM7242IPA or CD4017 will do that as long as the CLK signal is applied.
The output will be high for 50% and low for 50% of the total period.

 

Can you explain the need for this?

A differentiator circuit can turn the trailing edge of the 10-20-40 minute pulse into a very short pulse to clock the 4017 to advance it to the next battery. This drawing implies that R goes from the signal to GND, but it also can go too Vcc to select the other polarity of output pulse.

https://en.wikipedia.org/wiki/Differentiator

ak