Compact 10-minute delay with transistor, don't want to use special IC

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onoffman

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Compact 10 minute delay with transistor , dont want to use special IC

I am making 10min on delay

need ON delay circuit that uses minimal components
as there is space issue
so


>capacitor can be 220uF
>no special IC

using the circuit
https://www.2shared.com/photo/WppHQWWj/Ondelay.html
delay is 22Sec ;(

Please help need to make it atleast 10min
vcc 3v
it will power a beeper circuit(load)
 

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Re: Compact 10 minute delay with transistor , dont want to use special IC

You probably can do it if you use an N-MOSFET instead of a BJT, since MOSFETs have nearly infinite input resistance. All you need is one series R and one C to ground at the MOSFET gate.
 

Re: Compact 10 minute delay with transistor , dont want to use special IC

crutschow said:
You probably can do it if you use an N-MOSFET instead of a BJT, since MOSFETs have nearly infinite input resistance. All you need is one series R and one C to ground at the MOSFET gate.
Click to expand...
I'd expect turn-on to be very slow though.

Sounds like a job for a 555 timer. It's a fairly small chip and if it allows the use of a smaller capacitor, there could be an overall reduction in size.

edit: It will have to be one of the 555 variants that work on low voltage.
 

Re: Compact 10 minute delay with transistor , dont want to use special IC

Using a Mosfet with a very high value timing resistor and a very low leakage capacitor, the beeper will receive its power supply voltage very slowly then its oscillator might not begin the beeping.
The 555 or another monostable circuit will suddenly apply power to the beeper to ensure it begins beeping.
A 3V supply is needed so the 555 should be a Cmos 555 like an LMC555, TLC555 or the Intersil Ixx7555.
 

Re: Compact 10 minute delay with transistor , dont want to use special IC



low voltage 555is ruled out .importing 555 to here take 30days with air mail [country :INdia]
FET circuit may do that i suppose want to do with some common part like 2SK170
 

Re: Compact 10 minute delay with transistor , dont want to use special IC

2SK170 is a depletion mode JFET, you need an enhancement mode device.
I seriously doubt you can make a 10 minute timer with just a transistor and 2200uF capacitor. The time constant would require a high value source resistance and other effects like capacitor leakage would have a large influence. Your transistor would also need to draw minimal bias current hence the FET suggestion. The problem you will face with a FET is the turn-on voltage, most devices need more than 3V Vgs to become conductive.

You might be able to use a CMOS logic schmitt gate but a discrete transistor is not a good solution. Another possibility is a reset generator IC, there are some that use external timing capacitor and give a logic level output. They are often 3-pin devices so no bigger than a transistor.

Brian
 
Re: Compact 10 minute delay with transistor , dont want to use special IC

Hi

74hc1g14 in SC70 package.
But i'd prefer a ucontroller in SO8 to be independent of temperature and other passive device tolerances

Klaus
 

Re: Compact 10 minute delay with transistor , dont want to use special IC


Thanks , I am thinking my timer circuit with BC548, SK170 (yes single trans not possible )can work but now
its is ON---delay---OFF

Code: 
need to make OFF--delay--ON
tested the below one  it gives several minutes of time :) yay!!!

I need to test on 3V / 1.5v Vcc . But technically FET getting 3V or less here

Thanks 52KlausST,
74hc1g14 is good but need to import as not ready to find here i suppose .

Others FYR limitations
--want to use generic FETs/BJT
--no special IC /controller

The attached circuit should work with most generic FETs .
I want to keep my special AUDIO FET and use some other stuff
J112 is also there with me , that too is a nice device .

will check some other FET ....

Please advice to change the ON-SEQUENCE
-
 

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Re: Compact 10 minute delay with transistor , dont want to use special IC

Previous circuit was ON---delay--OFF

Placed the BJT to new position for OFF---DELAY--ON mode.
what do you think ?
 

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  • 10Min.png
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Re: Compact 10 minute delay with transistor , dont want to use special IC

If you use such a simple circuit, you must accept its inevitable poor and erratic performance:

-Because of tolerances, unit to unit timing variations can be 100% or more.
-Even on a tweaked unit, the actual time will vary with environmental conditions
-Aging may increase the capacitor's leakage to the point the circuit may not operate.
-Electrolytic caps have significant dielectric absorption.
-The actual LED will not change states immediately, but will change brightness gradually.
 

Re: Compact 10 minute delay with transistor , dont want to use special IC

Hi,

is an ATTINY a "special IC"?



8 parts and a bit of software.
2.4mA plus I_LED
3% precision.

Klaus
 
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Re: Compact 10 minute delay with transistor , dont want to use special IC


Thanks a lot.Yes there may be several -ves
this is somehow usable timer for a table buzzer .

regarding aging the cap will take a min 5year to show that (my assumption)
may be a suitable replacement with better cap needed for production circuits ..like tantalum

or multilayer MKP .47uf may do that 10 minute then it will be stable -for day to day use.

learning part is good so that i can design better circuits .

- - - Updated - - -

Situation is pretty tight
the table buzzer
is supposed to be easy to make for newbies .
i get all supplies from ebay US or element14 .

for newbies getting ATTINY and programmer jig is big thingy

KlausST said:
Hi,

is an ATTINY a "special IC"?

View attachment 107361

8 parts and a bit of software.
2.4mA plus I_LED
3% precision.

Klaus
Click to expand...

- - - Updated - - -

---- Finally the attached circuit does 10min delay ON timer job :grin:

Good news is LED just goes full ON instead of slow on.

The 10K from collector of Q2 is suitable value for that gives sudden ON.

Note:
capacitor value is 4.7uf for 10minute -sorry for error in diagram

we can go till 47uf for 10X long delay [ currently 4.7uf35V ]
I suppose 1000uf likes will give us 24hours or more

circuit is attached .

features
-10minute delay timer,full on after that
-Uses common parts no IC
-works with <3V also

Looking for improvements , specially 10M resistor if we can manage with smaller resistor


Modern day designer will prefer ATTINY . but newbies in electronics hobby in distant areas
specially in india can use this circuit .

Usage:
It will be a part of a small beeper in 3cm X2cm TICTAC box
**broken link removed**
 
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Re: Compact 10 minute delay with transistor , dont want to use special IC

The BC547 is simply making the circuit 100 times WORSE !!!!!!
 

Re: Compact 10 minute delay with transistor , dont want to use special IC

colin55 said:
The BC547 is simply making the circuit 100 times WORSE !!!!!!
Click to expand...

please explain . Functional wise or other .What can be better alternative
 

Re: Compact 10 minute delay with transistor , dont want to use special IC

colin55 said:
Go to my website where I explain the problems with hundreds of faulty circuits, where your circuit is included:

http://www.talkingelectronics.com/projects/SpotMistakes/SpotMistakesP21.html
Click to expand...

Read the site I disagree capacitor current is that big
Issue... Other variants like tantalum are there we can use those.
Wima MKS4 4.7Uf/63 possible candidate for serious product


next is simple 1meg and cap in series will not give 10minutes with sudden On...i will try that

PS:My be OT but I liked the first para in your site that is very true the academics dont teach real know how
100thanks
 
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Re: Compact 10 minute delay with transistor , dont want to use special IC

Hi,

to get an acceptable tolerance you need to switch at a n´know and reliable voltage level.
So how about building a (two) FET type comparator input stage and an output transistor. With positive feedback you get good output edges.

Maybe set the threshold to 100mV. Then you get 4.8 tau. With 10 minute you need a tau of 600s/4,8 = 125 s.
with 1000uF you need a resistor of 125k. should be possible.

An error of 10mV will give an error of about 13s. I don´t know if 10mV are realistic.

If you need schematics then google for "FET opamp input stage" or "FET comparator input stage".

Klaus
 
Re: Compact 10 minute delay with transistor , dont want to use special IC

KlausST ,
win FET must be a good option.
now letme talk about the space problem
the table buzzer has
a)two Bjts for Oscillator,earphone driver is used as buzzer [avoiding microbuzzer ]
b)on top of that this 10Min delay circuit + watchcells
c)a homebrew tilt switch will also go in
Case is small tictac box . >https://harjun.biz/v/wp-content/uploads/2010/11/TicTac_20CentCoin.jpg

A point to point soldering of superglued components I am planning .
I will put all in a thick paper,solder and slide in to the TicTac box.

This POC type device leading to limitations[X]
X--bigger capacitor
X--specialIC [difficult to procure for layman here ]
X--SMD components[many find difficult to procure]


I can guess the unit may give random times
as stated probably varying from 7-12minutes.

For now we can tweak a little /per unit to make it suitable.
I still desire some tweak for reliable switching .
But keeping smller sized discrete components .
 

Re: Compact 10 minute delay with transistor , dont want to use special IC

colin55 said:
Go to my website where I explain the problems with hundreds of faulty circuits, where your circuit is included:

http://www.talkingelectronics.com/projects/SpotMistakes/SpotMistakesP21.html
Click to expand...

Collin; excellent website. I have it bookmarked.
During my 40 year career in Electronics, I have interviewed literally hundreds of electronic engineers and technicians. Heck, some of them also have master degrees.
One of the first questions I asked the interview is precisely: have you built anything yourself? Or at least, have you fixed an electronics device yourself?

And you are absolutely correct, those who have, make the BEST Technicians/Engineers.

With respect to the circuit that onoffman is posting, I also agree with you that the electrocap's leakage current and other simplistic assumptions will eventually give him headaches.
I know from experience-- I built a similar circuit back in the late 70's and sold several dozens of it-- and it was a difficult experience.

But experience is never gained from someone else's pain. Experience is only acquired from personal pain.
 
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