Need help with 555 timer circuit development

use a 555 timer circuit to generate a variable 1 to 5 minute timer to alte rnate between 2 bank of batteries that are connected to a charger and a loa d. There are four switches where two are on when the other two are off. Pl ease send me a private email to if you are inte rested and can help. Thanks!

I'll provide advice for free. The 555 isn't really suited for producing 1 m inute to 5 minute time intervals. The CMOS versions have high enough input impedance to make the idea practicable, but keeping a printed circuit board clean enough to exploit this isn't all that practical.

This really is a job for single chip microprocessor clocked by a 32,768 Hz watch crystal. It will give you more accurate time intervals, and will be l ess tricky to get working.

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Bill Sloman, Sydney

Beg to differ; one 555 running at (say) 1KC can drive a second one set like a 30:1 divider which in turn can drive a third set like a divider, etc; can get down to days with good accuracy.. But the micro gives excellent precision and accuracy with no RC tweaking.

Or a CD4060, this timer has a 14 bit divider attached. it's used in toasters etc 5 minutes is no problem.

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umop apisdn

That sounds like making life unnecessarily difficult just to use 555's for the job. A CMOS 555 followed by a divide by 2^N chip should do the job admirably (although I think a PIC might be easier/cheaper).

A CMOS 4060 might well do it in a single chip oscillator & divider.

(for the benefit of the OP)

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Regards, 
Martin Brown

to use a 555 timer circuit to generate a variable 1 to 5 minute timer to a lternate between 2 bank of batteries that are connected to a charger and a load. There are four switches where two are on when the other two are off. Please send me a private email to if you are i nterested and can help. Thanks!

1 minute to 5 minute time intervals. The CMOS versions have high enough in put impedance to make the idea practicable, but keeping a printed circuit b oard clean enough to exploit this isn't all that practical.

Hz watch crystal. It will give you more accurate time intervals, and will be less tricky to get working.

ng.

I think you've just gone mad. Iterating 555's just gives a linearly increas ing delay, not a multiplication.

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Bill Sloman, Sydney

He's talking about injection locking the slower ones. The problem is that the slowest one still has all the problems of a free-running 555 at that speed.

If the OP can't design his own 555 circuit, a 4060 is probably good medicine.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 

NOBODY said anything about multiplying. Dividing is an inverse function.

Absolutely! I just stuck with the 555 to make a point that they are useable, and with the right division ratio (no more than 30:1) and stable parts, one can get many hours for timing.

I guess a timer driving a Flip flop would do..

The Q and /Q can drive some trannies to switch the coils in. Not sure if the timer can spand that far however, you can switch in/out between flips flops to correct that problem.

Jamie

use a 555 timer circuit to generate a variable 1 to 5 minute timer to alte rnate between 2 bank of batteries that are connected to a charger and a loa d. There are four switches where two are on when the other two are off. Pl ease send me a private email to if you are inte rested and can help. Thanks!

I just want to thank everyone for your invaluable input. Since this is way over my head, I still need help and would contact some of the folks who had replied and shared their contact information. Thanks again, I do apprecia te the suggestions.

-Toyin

Since nobody else acknowledged the elephant in the room, I'll take a stab. Your objective isn't clearly stated... If you're charging one battery while loading the other, What happens at the switchover? Break before make glitches the power off. Make before break risks breaking something with high current between the batteries.

It's likely that you'll have issues well beyond timing. The microprocessor solution gives you the opportunity to address them. And having A/D converters available lets you monitor everything and possibly decide that time is not the optimum switching criterion. Also lets you log performance and shove data out a LED that that you can read with a phone/PDA.

You're likely to be disappointed with any rational approach to a 5-minute analog delay.

I'd back up a level in the system design and approach the whole range of issues.

I'm curious to know exactly what problem the switchover solves???

look at

cheap, easiest to use and will do the job

Just to add some numbers to that 555 v uP decision, LMC555CMN from Farnell costs 0.29 each on a reel of 5k. You can buy an 8 pin Cortex M0 for 0.33 (3k price break)(and there will be cheaper processors if you look around). The extras to make the 555 give reliable 5 minute delays

Michael Kellett

use a 555 timer circuit to generate a variable 1 to 5 minute timer to alte rnate between 2 bank of batteries that are connected to a charger and a loa d. There are four switches where two are on when the other two are off. Pl ease send me a private email to if you are inte rested and can help. Thanks!

Ummmm...if you have the power for a charger then you have power for the loa d, no batteries, timers or switches necessary.

You may send US$500 to:

Fred Bloggs XX XXXX XX XXXX, XXXX USA

use a 555 timer circuit to generate a variable 1 to 5 minute timer to alte rnate between 2 bank of batteries that are connected to a charger and a loa d. There are four switches where two are on when the other two are off. Pl ease send me a private email to if you are inte rested and can help. Thanks!

Are you toyin' with us? :^) I can still remember the first 555 time circuit I made for myself. I knew next to nothing and made a very drifty clock. As long as you don't need too much accuracy the 555 or 4060 should be fine.

George H.

Sure, but since the OP isn't comfortable building a 555 circuit, setting up a development system, learning C or PIC asm, and getting it working is probably more than a 4d job. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 

Given the lack of info on the objectives and quantities, it's difficult to speculate.

My point, based on 40 years of watching very smart engineers bang their heads against the wall trying to use devices unsuited for the job, is that reexamining the system architecture is likely to be more fruitful than trying to design around all the subtle gotchas required to get a reliable 5-minutes out of a 555.

I'm all for using tools and devices matched to the designer's skills and experience. I suggest that it's far easier to learn a very valuable programming skill that, in this case, requires little more than copying an example program, than to learn all about current leakage on a circuit board under reasonable environmental stresses.

If you don't have the skill for either task, might as well learn the skill for the one likely to work.

s

but he'll know how to do it next time :)

if lazy get something like this:

-Lasse

BITD when you had to use wet electros for the job, I agree. I suspect that a polymer aluminum might do fine with a CMOS 555, inelegant as that is.

1meg * 330 uF makes a TC of 5.5 minutes. Connecting the cap from the trigger input to VDD makes the leakage shorten the delay rather than lengthening it (perhaps indefinitely).

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant