Splash

Hi everyone,
Firstly I've been looking for a forum like this one for a long time, its great to see a popular electronics forum with people helping eachother.

Ok, now to my project.
I am trying to build a timer for mains appliances i.e. stereo's, tvs etc. that on the outside is a very simple box that you plug into the wall, then turn a dial to the length of time before it cuts the power to whatever device you have plugged in to 'this' device.

I've found a couple of kits on an american site that do this job, but 1 they are from America which complicates postage etc. plus 2 I'd prefer to make it from scratch. But so you can get a better idea of my projects here are the 2 kits.
http://store.qkits.com/moreinfo.cfm/K6200
http://store.qkits.com/moreinfo.cfm/K8075

Now, I've sketched out some quick ideas of how it may work, but please be warned I am a complete amatuer And my schematics may be completely wrong.

I was hoping some of you guys and girls could help me out in any way you can? i.e. tell me where my design is wrong, suggest how I could achieve this with a completely different circuit etc.

Here are a couple of the thoughts I've had so far. (where the +9v comes in will be after a transformer)



I highly appreciate any help you can give me with this

Splash Δ

ljcox

Your circuits won't work without some refinement. I suggest you do a search of this forum. There have been plenty of timer circuits posted in the past. I've posted some myself.

There are three solutions:-
1. an RC timer - this requires a Schmitt Trigger to detect when the capacitor has charged to a particular level. It is a crude solution so you can't expect it to be very accurate.

2. A counter driven by a crystal or from the AC mains. This will be very accurate.

3. As for 2. but use a PIC instead of a counter. This is more flexible and will result in less components since the logic and counting is done in the PIC.

You have not indicated where you live. Several electronics shops sell kits in Australia.
See www.jaycar.com.au, www.altronics.com.au, www.dse.com.au

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Len

Splash

Hi Ljcox, thanks for the reply.
I've spent several hours searching the forum but havn't been able to find anything quite right for my project. However after googling for a while I came accross this circuit http://uk.geocities.com/ronj_1217/c4060s.html

I was looking at the second of the 2 circuit designs as it de-energizes the relay and i.e. cutting power to the appliance.

However I was hoping someone could help me adapt the circuit to my needs either by redesigning or simply explaining where the extra components would need to go.

As far as I can see the circuit is missing the ability to be variably changed by a user, either by potentiometer or rotary switch.

Can anyone help me with this?

Oh and Im from england as is this circuit which is great as it tells me the component codes for maplins

mcs51mc

Hi Splash,

The kits from your first post are made by Velleman. Check these
http://www.velleman.be/be/en/product/view/?id=9317
http://www.velleman.be/be/en/product/view/?id=363346

So I think you can easily find them overhere in Europe, check also www.Conrad.de

About the other ckts: Read the datasheet of the 4060 first, then be creative and tell us how you can verry easily modify the ckt to have variable timing.

Finally: check this one http://www.velleman.be/dealer/search...3&cid=57&did=4

Regards

Splash

Hi mcs51mc,
Thankyou for the links, those kits do pretty much exactly what I'm after they are variable by the changing of a jumper block which isnt really suitable as I want it to be very easy to use for people who arn't comfortable with poking around on PCB's plus I much prefer to make things from scratch, I find it far more satasfying

I've been playing with the 24 hour timer schematic and have come up with this, I would really appreciate it if someone could give it a look over and see if I have any big problems?

Thankyou all

Attached Images

Timer Circuit.jpg (146.4 KB, 21 views)

Splash

Ah, on the above attached schematic I missed a flying wire between the 1st pole in the rotary switch and in between D1 and R5 just pretend its on there

Hero999

That will work but it won't be that accurate; is accuracy important for your application?

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Splash

Accuracy is important to a degree, as long as it isnt out by more that a few minutes it wont be a problem, do you think it will be less accurate than that?

Hero999

That depends on the tollerance of the componants.

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Splash

Ah ok, Im not sure of what tolerence effects, I'm assuming the only ones that would matter were the transistor, capacitors and relay? These are the components that I'm planning on getting. Any chance you could give them a once over?

Relay
Transistor - 2N2907A
C3 - 10uF
C1 & C2 - BX03D

Hero999

No offence but obviously you've not been in engineering for very long.

A componant tollerance is the amount a componant value can vary from the stated value. The transistor and relay make no difference, the only componants that make a difference to the delay is the timing capacitor and resistors.

The capacitor is likely to have the largest tollerance so it will affect the delay more than the resistors. The capacitor has a tollerance of +-20%, therefor it can be as much as 20% bigger or 20% smaller than 10µF, therefore its value can range between 8µF and 12µF.

Why are you using a more expensive non-polarised 100V electrolytic capacitor when a cheep polarised 10µF 25V unit will do?

Non-polarised means it will work on AC, your project is DC so whilest it will work, it isn't required.

Look up the tollerance of the resistors, then recalculate everything for the upper tollerance value of capacitor and resistors then the lower tollerance values, then see if the level of accuracy is acceptable.

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Splash

Haha no offence taken your completely correct.
Thankyou for explaining it makes sense now. I'm using the non-polarised capacitor as i was told it needed to either be non-polarized or 2 x 22uF Polarised back to back by the build instructions.

Ok, so all the resistors are +-5%

my original C1 & C2 were +80% which seems huge so I have changed to these;
C2 + C1 As they are +-20%

C3 is +-20%

So am I right in thinking it will be a maximum of 20% inaccurate?

Hero999

All they are is decoupling capacitors, not timing capacitors so it won't make any difference. Please re-read my above post, you only have to worry about the components that directly effect the timing.


Yes, try using a crystal oscillator.

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Splash

Ah ok, well for my project 20% would be about the limit of acceptable. Would using a crystal oscillator mean an overhaul of the circuit or simply adding something? ok I'll switch to a polarised cap.

Also I have never used mains power in a project before, I'm looking at this transformer 240v step down to 12v
Would a transformer like that output in DC? or will i need a seperate component to perform that function?

House0Fwax

The output from that would be AC. You'd need to 'rectify' it to DC using either 4 diodes or a bridge rectifier.
There are many schematics on the net for power supplies.