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Author Topic: How do i make a timing circuit?  (Read 2704 times)

tj22

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How do i make a timing circuit?
« on: March 21, 2012, 02:23:18 PM »

Hi, hopefully someone on here could help me. im trying to make a circuit that will time out after a preset time.

i have looked at 555 timers, but its all beyond me.
what im trying to do is to create a circuit that when i press a push-to-make button it will complete the circtuit. then after 30-120 seconds it will automatically turn off until the buttong is pushed again and then it will do the same. so i dont need a repeat function or a self timer on setting. i hope that this makes sense. none of the operation will be via RC its all hard wired in.

Many thanks for any help.
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ACTion

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Re: How do i make a timing circuit?
« Reply #1 on: March 21, 2012, 02:37:50 PM »

This willo do the job you require http://www.maplin.co.uk/universal-timer-kit-3315
I've made a few of these and they work very well. Easier than trying to make your own on ruddy Veroboard! 12v DC supply required and you can increase the big capacitor size to 220uF if you need a longer time-on period.
Dave M
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tj22

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Re: How do i make a timing circuit?
« Reply #2 on: March 21, 2012, 03:35:19 PM »

Hi, thats great, and tahnks for the fast reply. do you know if there is anyway to increase the 2A rating on this switch? also i see that there are two buttons? im guessing one is turn it on, but whats the other for? cheers
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essex2visuvesi

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Re: How do i make a timing circuit?
« Reply #3 on: March 21, 2012, 04:20:52 PM »

use the on board relay to switch a beefier relay?
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malcolmfrary

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Re: How do i make a timing circuit?
« Reply #4 on: March 21, 2012, 04:41:35 PM »

What he said about using the output to switch a relay that carries the current you want.
Looking at the "question" page  http://www.maplin.co.uk/universal-timer-kit-3315  others want it to do something similar, but the answer is that "No sorry this product does not support that."  However, the assembly/testing instructions from Velleman  http://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k2579.pdf
indicate that it does.  Wont be the first time that Maplin have tried to ditch a worthwhile product by being utterly clueless.  While it has a stop and start button, the start operates the relay and starts the timer.  If there is a need to release the relay early, thats what the stop button is for.  Just my reading.
If you want to go the DIY route, look up "monostable mulivibrator" in the "millions of things to do with a 555 timer" book.
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tj22

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Re: How do i make a timing circuit?
« Reply #5 on: March 21, 2012, 04:47:26 PM »

i was thinking along those lines. im just trying to get it right in my head as im not the best at electronics. so i basically need two circuits. one for the first timing switch. this will then switch the relay and turn on the main circuit. then when the timer switch switches off, it will switch the relay which in turn with break the main circuit so everything stops? is that correct? maybe a relay such as this? http://www.maplin.co.uk/10a-dpdt-miniature-relays-37518

this first circuit only works on 12v, so if i connected this circuit to a relay, that could for example handle 40A at 240v i could connect the main circuit up to a mains power supply and the original timer switch to a 12v supply?


malcolmfrary, thank you for your clarification on the two swtiches. that makes plenty of sense. i will have a read of the pdf file you have posted too.

many thanks

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ACTion

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Re: How do i make a timing circuit?
« Reply #6 on: March 21, 2012, 05:02:22 PM »

All you need do is take two leads from the PCB where the 2A relay coil would normally fit and run them to the coil of a remote relay with a 12v DC coil. As long as this relay will handle the load you require then you don't need the original relay at all.
DM
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dodgy geezer

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Re: How do i make a timing circuit?
« Reply #7 on: March 21, 2012, 07:37:46 PM »

All you need do is take two leads from the PCB where the 2A relay coil would normally fit and run them to the coil of a remote relay with a 12v DC coil. As long as this relay will handle the load you require then you don't need the original relay at all.
DM

but you would want to be sure that the kit can put out enough mA to switch that big relay coil....  If you wanted to switch, say, a water heater you'd probably want a 30A relay, with a coil drain of 100mA. I don't know if the BC547 would need to be changed - ACTion would know these things....

And you might prefer to put the whole caboodle in a box with mains in and mains out, and power all the circuits from a little transformer/rectifier....
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malcolmfrary

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Re: How do i make a timing circuit?
« Reply #8 on: March 22, 2012, 11:18:55 AM »

If the supplied relay contact is used to switch the bigger, meatier relay, the circuit can run off one supply, the big relay (and whatever that is controlling) can be on another supply since the coil and contacts are (or should be) electrically isolated from each other.
The important things to look at are
1 What current does the relay contact need to carry?
2 What voltage do the contacts need to stand up to?
3 What is the intended voltage to operate the relay coil?
4 What current is required to operate the relay coil?
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HawkEye

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Re: How do i make a timing circuit?
« Reply #9 on: March 22, 2012, 02:22:53 PM »


It's a bit difficult to suggest an answer without knowing what you're switching but there's a range of timer modules here -

http://cpc.farnell.com/jsp/search/browse.jsp?N=411+2005+207195&Ntk=gensearch&Ntt=momentary+timer&Ntx=mode+matchallpartial

And perhaps a solid state relay if you need more Va on mains related voltages.

http://cpc.farnell.com/jsp/search/browse.jsp?N=411+2005+206972&Ntk=gensearch&Ntt=solid+state+relay&Ntx=mode+matchallpartial


HawkEye
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More Coffee

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Re: How do i make a timing circuit?
« Reply #10 on: March 23, 2012, 06:19:21 AM »

You can use a transistor to pull down the 12V source to switch the heavy relay.

this is a circuit I used to get a 3v output to turn on a 12v relay..Make sure you use the 1n4001 diode as the coil will have alot of back emf and it hast go somewhere. I havent tested it ..but in lue of the 47K resistor start with a 100k and get rid of the 1n4148 zener diode.

The led and resistor is just there to notify me that the relay is on,also to let me know theres power to the relay if the switched current isnt working,,letting me know that the relay is shot.

for what is worth the most current Ive had drawn by a similar realay  is less than 100ma..
I have a circuit that switches 16 relays in a bidirectional chaser array that use'a less than 200ma at full speed..and about 110ma at low speed.
The relay's only draw 30ma@12v..the 555 Timer can sink 25ma ..it can sink 200ma but lets not get carried away..

INCREASING OUTPUT
CURRENT
The 555 will deliver 200mA to a load but the chip gets extremely hot (12v supply). The answer is to use a buffer transistor.
For 200mA, use a BC547 or equivalent.
For 500mA use a BC337 or equivalent
For 1A, use a TIP31 or equivalent.
For 3A - 5A use a BD679 or equivalent with heatsink
For 5A to 10A use TIP3055 with heatsink
 
This is basicly what i did in my own schematic,,using a transistor to sink the current to the load


You can fill yer boots full  of 555 circuits here..
http://talkingelectronics.com/projects/50%20-%20555%20Circuits/50%20-%20555%20Circuits.html#H
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