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Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: Bill D203 on January 19, 2011, 08:57:30 PM

Title: Simple 555 timer circuit.
Post by: Bill D203 on January 19, 2011, 08:57:30 PM
Dose anyone has a simple timer circuit???
All i need it to do is when power (12DC) is put on it after 3/10 secs ( set by a pot) pull in a relay and stay that  way till the power is taken off. I need a relay type output stage. I am happy to build it myself on Strip board as PCB are a bit ott for what i want it to do.
Cheers
Title: Re: Simple 555 timer circuit.
Post by: ACTion on January 19, 2011, 11:12:27 PM
PM sent.
DM
Title: Re: Simple 555 timer circuit.
Post by: John W E on January 20, 2011, 09:50:34 AM
Hi Bill will this one do the job ?  ;)

aye
john
Title: Re: Simple 555 timer circuit.
Post by: PMK on January 20, 2011, 10:40:20 AM
John, your circuit will certainly do what Bill wants it to do, but in order to trigger the timer it means he would have to push S1 to momentarily ground the trigger input (pin 2). My take is that Bill wants it to trigger as soon as power is applied - in which case he could simply omit S1 and then tie pin 2 permanently to ground. He might also consider upping the value of R2 in order to keep the current draw to a minimum.
Also, depending on the relay coil, he might want to omit D1 and stick a driver transistor before the relay.

Bill, if you're earwigging, did you get my message regarding your KillBill unit? At your convenience, anytime from tomorrow onwards, can you give me holler on my landline that I can clarify a couple questions?
Title: Re: Simple 555 timer circuit.
Post by: rathikrishna on January 20, 2011, 02:29:33 PM
Hai Blue bird..thanks for the effort...now i am too happy to see a simple circit in MBMH...so its a real place of genius..so thanks once again..please post some more circuits with CD series Ics, and ULN s...great promotion to our own ideas...
Title: Re: Simple 555 timer circuit.
Post by: DavieTait on January 20, 2011, 02:43:10 PM
I had to build a 555 timer circuit ( binary counter with LED's as the display ) back in 1984 as one of my first practical projects when I did my electrical and electronic engineering ONC..... probably still got the thing in a box somewhere lol
Title: Re: Simple 555 timer circuit.
Post by: rathikrishna on January 20, 2011, 02:50:17 PM
Sure Davi..its true..the older projects..but still its far usefull to us...i remember, that i made a KNIGHT RIDER scanning light with it...so nice..
Title: Re: Simple 555 timer circuit.
Post by: Bill D203 on January 20, 2011, 05:28:57 PM
John, your circuit will certainly do what Bill wants it to do, but in order to trigger the timer it means he would have to push S1 to momentarily ground the trigger input (pin 2). My take is that Bill wants it to trigger as soon as power is applied - in which case he could simply omit S1 and then tie pin 2 permanently to ground. He might also consider upping the value of R2 in order to keep the current draw to a minimum.
Also, depending on the relay coil, he might want to omit D1 and stick a driver transistor before the relay.

Bill, if you're earwigging, did you get my message regarding your KillBill unit? At your convenience, anytime from tomorrow onwards, can you give me holler on my landline that I can clarify a couple questions?
Hi Pete
I did try to ring both your home & mobile number with no replys. I will if i get a chance callyou Friday. Cheers for now.
Title: Re: Simple 555 timer circuit.
Post by: Bill D203 on January 20, 2011, 05:32:21 PM
Hi Bill will this one do the job ?  ;)

aye
john
Cheers for the circuit. If I get a chance this weekend i will try and build it without the switch as it just needs to time as soon as power is put on to it.  :-))
Title: Re: Simple 555 timer circuit.
Post by: PMK on January 20, 2011, 07:00:31 PM
Hold the front page!
With absolutely no disrespect to Bluebird, the circuit shown above will not work as Bill wants it to work. Being that the 555 chip is configured for monostable mode means that the relay will de-energise as soon as capacitor C1 reaches approximately two thirds of the suppply voltage... even if pin 2 of the chip is permanently tied to ground. Bill wants it that the relay will energise, and stay energised, after a preset time - which is user-adjustable by the pot - from the moment that the power is applied.

Am working on the solution as we speak. Standby.......
Title: Re: Simple 555 timer circuit.
Post by: John W E on January 20, 2011, 07:16:31 PM
 :-))

Hi PMK good job one of us is awake ...... hope this one works and is right......if I get this one wrong I WILL PUT ME GLASSES ON AND FIND THE BIG BOOK

:-)

aye
John
Title: Re: Simple 555 timer circuit.
Post by: PMK on January 20, 2011, 08:41:00 PM
Hi, John.
Again, with all due respect, your 2nd circuit is also of the monostable flavour. Pins 6 and 7 are tied together and pin 2 is again used as a trigger input. In effect it means that when pin 2 is grounded, the relay will energise but will then turn itself off when capacitor C1 is charged to roughly two thirds of the supply voltage. If I understand Bill correctly, he needs it to work that the relay kicks in after a short delay of the power supply being conected, and once the relay has energised it needs to stay energised for as long as the power supply is connected (Bill will have to correct me if I'm wrong on this or if I've misunderstood what he's asking).
The attached circuit will energise the relay after a preset time of the supply being connected and then remain on. The 100uF capacitor in conjunction with the 100K trimpot and 10K series resistor will yield a delay-on-time of anywhere between 1 second and 12 seconds.
Note that pin 7 - the so-named discharge pin - is not used in this application.

I'm gonna feel a proper berk if this is not what Bills wants.
Title: Re: Simple 555 timer circuit.
Post by: PMK on January 21, 2011, 01:40:25 AM
..please post some more circuits with CD series Ics, and ULN s...

Rathikrishna, I am not sure what you mean by ULN's. Could it perhaps be a typing error for ULA's?
You can find two or three simple circuits using CD series ICs from the "R/C Gadgets" menu on the left-hand side of this page: http://www.pm.keirle.com/
Title: Re: Simple 555 timer circuit.
Post by: philk on January 21, 2011, 08:08:50 AM
i think what she means by uln series is the uln series of darlington arrays.
see this link

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&binCount=33&Nty=1&Ntx=mode%2bmatchallpartial&Ntk=I18NBrandPartNumber&Ne=4294957561&Nr=AND%28avl%3auk%2csearchDiscon_uk%3aN%29&N=4294611825&LanguageId=en&Ntt=*uln2*
Title: Re: Simple 555 timer circuit.
Post by: malcolmfrary on January 21, 2011, 10:16:46 AM
What is the relay doing?  This is important as relays having high current contacts usually have a high current coil to give the power needed to shift the heavier contacts, thus need a driver circuit capable of handling that current, and since this is to be "permanently" operated, could form a significant drain of battery power.
Is it just switching the negative line through to whatever its operating?  If so, then one of the ULN series Darlington arrays mentioned above could do the relay's job perfectly adequately (current requirements permitting), and would need little more than a zener diode, a capacitor and resistor to form the time delay for switching on after power up.
Title: Re: Simple 555 timer circuit.
Post by: PMK on January 21, 2011, 11:21:31 AM
i think what she means by uln series is the uln series of darlington arrays.
see this link...

Ah yes, the ULN Darlingtons! Yep, I'm with it now. Thanks for the reminder.
For some reason I'd clean-clear forgotten about ULN's in that sense and my mind started wandering towards Uncommitted Logic Arrays. (Anyone remember those?)

Malcolm, ref the relay: As mentioned in post #3, if it were me I'd be inclined to stick a relay driver transistor in there. I have no idea what it is that Bill wishes to control with the relay and no idea of his relay specifications, only that he asked that the actual timing to be done with a 555 chip. Being that the 555 can sink/source up to 200mA.....
You get the picture.
Title: Re: Simple 555 timer circuit.
Post by: rathikrishna on January 21, 2011, 01:04:16 PM
nice...
Title: Re: Simple 555 timer circuit.
Post by: PMK on January 23, 2011, 03:33:56 PM
Bill, I managed to shoehorn the timer circuit inside a box of the same size as your KillBill unit.
It's your lucky day because I happened to find a few mini relays which pull just a measly 22'ish millamps when energised. The whole caboodle pulls a total of 30mA, therefore it shouldn't put too much of a drain on your battery. You have the choice of using the normally-open or normally-closed contacts, rated at 1Amp max. - should be fine for your purposes.
Unfortunately, by the time I squeezed in the relay, and the screw terminals, the pot, the chip and all the other gubbins, means there was no room left on the board to have a protection diode for the power supply. You need to make sure to connect the red wire (plus symbol) to positive, else you'll end up frying the chip.
The on-board trimpot lets you adjust the on delay from 1 second to roughly 12 seconds.

I'll bung it in the post to you on the morrow.
Title: Re: Simple 555 timer circuit.
Post by: Bill D203 on January 23, 2011, 05:48:46 PM
Bill, I managed to shoehorn the timer circuit inside a box of the same size as your KillBill unit.
It's your lucky day because I happened to find a few mini relays which pull just a measly 22'ish millamps when energised. The whole caboodle pulls a total of 30mA, therefore it shouldn't put too much of a drain on your battery. You have the choice of using the normally-open or normally-closed contacts, rated at 1Amp max. - should be fine for your purposes.
Unfortunately, by the time I squeezed in the relay, and the screw terminals, the pot, the chip and all the other gubbins, means there was no room left on the board to have a protection diode for the power supply. You need to make sure to connect the red wire (plus symbol) to positive, else you'll end up frying the chip.
The on-board trimpot lets you adjust the on delay from 1 second to roughly 12 seconds.

I'll bung it in the post to you on the morrow.
Pete.YOUR A STAR MATE.  Thanks very much.
Title: Re: Simple 555 timer circuit.
Post by: rathikrishna on January 24, 2011, 09:04:12 AM
Friends..ULN s are used along with timers to control greater loads ith muti channel switching...i have many circuits with me..so i will post it .so i hope some will help you all...
Title: Re: Simple 555 timer circuit.
Post by: kalyanprodhan on January 24, 2011, 08:42:09 PM
A Transistorized ckt is given.
Use 8550 for driving relay in place of BD136.

Working Principle
==========
The capacitor got charged through a (12-3.3 = 8.7) volt rail through 100K Pot and makes on while voltage >5.7 volt (5 Volt Zener + .7 volt Base emitter drop. Generally RCmax =  100K x 100uF = 10 Sec. therefore this can be linearly adjusted by a Lin Pot. Another 1N4007 may be given from BD136 collector to RC Node through 1K resistance so that Switching may be fast. Again, 1M of BD136 base resistance stops the unwanted turnon. 1N4007 parallel to Resistance can make the capacotor discharge through 1 KOhm. If you want more time delay, you can use higher zener in place of 5 volt or make RC time constant larger.

But I find that Capacitor charging rail voltage (here 12-3.3 = 8.7 Volt) and the reference voltage to compare (Here 5 volt) ratio works better at .632 (More accurate and robust.
Title: Re: Simple 555 timer circuit.
Post by: rathikrishna on January 25, 2011, 06:44:03 AM
Hey Kalyan...great thanks for the circuits...expecting more from you....some nostalgic...thank you...have you started your model work...dont be lazy....
Title: Re: Simple 555 timer circuit.
Post by: malcolmfrary on January 25, 2011, 02:40:33 PM
Liking simplicity, I feel that this should be considered.  A bit of crossed fingers hoping the drawing comes through....
At switch-on, the capacitor charges toward line voltage.  Eventually (depending on the setting of the 1M variable resistor), the Zener voltage is reached, and Q1 switches on.  This switches on Q2, which switches Q3, whic applies current to the relay coil.  The relay then operates and stays that way until power is disconnected.
The transistors are not critical, being basically any small switching type of the correct polarity.  Q1 and Q3 could be part of a ULN array, Q3 could be several elements in parallel, and could switch several elements.
Connecting a 1M resistor across the power wires would ensure that during the switch-off time the capacitor would be fully discharged to ensure that the timing would be more reliable.
Title: Re: Simple 555 timer circuit.
Post by: kalyanprodhan on January 25, 2011, 02:45:49 PM
But this circuit cannot make same delay just after making off and again on.
The Capacitor charge resides in it and if again make on, you cannot get the 3-4 second delay.
In my crcuit, a small diode and 1K does the job and that is why another diode and 1k used while making 8 Volt rail.

Thanks
Title: Re: Simple 555 timer circuit.
Post by: malcolmfrary on January 25, 2011, 03:01:38 PM
Read the last line of my previous post.
Then consider that total accuracy to the last microsecond is not required - its just a relay that's being operated a few seconds after power on, and relay operating time itself is not one of life's constants - in electronic terms, it can be considered an age.
For operating a non-specific relay on a specified voltage (see the original post) no great complexity is needed.  Thinking about it further, the transistors could be dispensed with and replaced by an SCR.
Title: Re: Simple 555 timer circuit.
Post by: Bill D203 on January 25, 2011, 04:12:27 PM
Cheers PMK / Pete.
The timer got here today and is just the jobby :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-)) :-))
Must buy you a pint  very soon :} :}
Title: Re: Simple 555 timer circuit.
Post by: PMK on January 25, 2011, 05:35:34 PM
Would love to take you up on your offer of a pint, but the man from Delmonte (el cardiologist), he say NO!
Just glad to hear that the timer gizmo does what it's supposed to do.
Health permitting, give me a couple days and I should have your KillBill failsafe gubbins working.

Later.....
Title: Re: Simple 555 timer circuit.
Post by: malcolmfrary on February 05, 2011, 04:16:22 PM
Yet another thought after finding the Practical Electronics Handbook download.
This one uses an SCR, not often used in DC applications because they don't like switching off. 
At switch on, the capacitor charges up to the zener voltage.  At that time, Q1 passes current to the gate of the SCR, which switches on, and stays on until power is disconnected.
At switch off, the capacitor will discharge via whatever was also connected to the battery (a 1M resistor across a and k of the SCR would ensure discharge)
Sadly, craplins, while they do have one SCR listed, don't want to sell any.  They can't be bothered to show any useful information, including the type(!).  Fortunately, ESR have a few listed, and data for these can be found.
Title: Re: Simple 555 timer circuit.
Post by: PMK on February 05, 2011, 06:09:34 PM
Ah, that's nice. The beauty is in the simplicity. I have a few SCRs in the junquebox - TO92 types, but no idea of their exact specifications.
If I may, just two (albeit very minor) questions:

1) Should the Zener read 4v7, or 4.7v - as opposed to 4k7?
2) I'm not familiar with seeing the 10k resistor tied to the wiper of the pot in this particular instance. Could I pick your brains and ask what are the benefits of doing it that way? I'm more used to seeing the 10k being in series with the leg of the pot on the 'hot' rail, and the wiper usually connected to, say, the Base of Q1... if that makes sense.

The 1-meg res' across A and K would be my prefered choice of discharging the cap'.
Title: Re: Simple 555 timer circuit.
Post by: malcolmfrary on February 06, 2011, 10:48:50 AM
4V7 is just another way of saying 4.7v, usually thats what appears on the zener anyway, decimal points tend to get lost on the component, which can be tricky.  It also helps confirm that its a zener diode under consideration.
The wiring of the slider resistor is purely arbitrary - its just there to make sure that the capacitor does take some time to charge.  The results would probably be the same if the connection between the top of the pot and the +ve line.  The pot is what adjusts the timing of the charge, Q1 is an emitter follower observing the voltage and presenting it to the zener diode at a lower impedance, so Q1 does need to look at the capacitor voltage.  The pot should give a good range of times, changing the capacitor would give a further range, as would using a different voltage zener.
There are lots of ways of skinning this particular cat, and its quite possible that the result could be achieved with yet fewer components, (741, pot on one input, R on the other, transistor output springs to mind) but unless I accidentally have a large cheese butty and a flagon of something potent for supper one night, probably not me.
Title: Re: Simple 555 timer circuit.
Post by: PMK on February 06, 2011, 06:04:27 PM
"4V7 is just another way of saying 4.7v...."

Absolutely. It's just that your "4K7" kinda threw me. I guess I'm more used to seeing the "K" when it comes to resistance.
(Okay, okay - I know. I'm just being nit-picky again is all.)

<10K wiper resistor>
"The results would probably be the same if the connection between the top of the pot and the +ve line."

Ah, that's what I wanted to hear. Thanks for the heads-up. The rest of the circuit is pretty much self-explanatory, but thanks for the detailed info. just the same.
Concurred, ref the 741 - in which case hysteresis wouldn't even rear its ugly head.

Here's to a cheese sarnie and a flagon of scrumpy.
Title: Re: Simple 555 timer circuit.
Post by: malcolmfrary on February 06, 2011, 09:39:02 PM
Quote
Absolutely. It's just that your "4K7" kinda threw me. I guess I'm more used to seeing the "K" when it comes to resistance.
Quite right, "K" should have been a "V".  Don't know where that crept in.  Probably a  Silver moment  {:-{ (mental note to self - just the one quart of absinthe on the breakfast wheaty-bangs).
Hysteresis shouldn't really be a problem with a power on delay.  When power goes off, the relay should release immediately - the only theoretical problem is making sure that the capacitor is sufficiently discharged before switching on again to keep the required delay.