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5 x 555Timers


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Hi

I am working on a project which needs 5 timers.
First, please see the flow chart.
Next, the time graph for better understanding my requirement.
Finally, the proposed schematic.

I shall appreciate, valued suggestions to finalize my project.

By the way, being a hobbyist, I have limited knowledge of electronics.

Thanks.

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I have a couple of suggestions:

If you must use the old 555 timer, opt for the NE556, which has two in one package.

I would suggest an alternative to the old 555 timer - sort of project can be simplified using a microcontroller making it possible to reduced the entire project to a single 8 pin DIL and a few transistors or another driver IC to drive the relays.

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Other than a microcontroller, I was going to suggest the CD4069 which can be used to make three monostables per chip (two ICs) but then I realised that the output drive is pathetic so additional driver transistors would be required.

I still recommend the microcontroller, buy a programmer (here's a good supplier: http://www.piccircuit.com/) and check out the following tutorial sites:

http://www.gooligum.com.au/tut_baseline.html - deals with the baseline (very cheap) PICs.
http://www.winpicprog.co.uk/pic_tutorial.htm - another good site.

I'm currently learning about MCUs and I think the time you would spend, designing a PCB for and assembling the complicated project would be better invested in learning new skills, such as working with PICs.

I have a similar project in the pipeline (an extractor fan timer) and rather than bothering to build the circuit I designed (a 555 plus a couple of logic ICs), I've bought a programmer and am learning to program PICs. I've just got past the turn on an LED tutorial (baseline) and I'm in the middle of the flashing LED tutorial. I've done assembly programming before for the PC so it shouldn't be too hard to learn.


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Hmm, your advice is good. But, in my area all those components are very cheap. And I am pretty sure to complete the PCB for about $20-25 only, including the relays!!!

I had enjoyed programming a lot from 1988-2002. I understand that computer, electronics etc. are all to get maximum benefit with lesser effort/cost. But, I like working with basic components. PIC or PICAXEs are just like computer programming, I cannot enjoy the electronics with them. Anyway, that's my thinking. Maybe I am wrong.

Thanks for your help/suggestions.

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You're in a better position than most to learn about MCUs.

In this case, cost-wise both solutions will be similar as the price of the relays will dominate. I've had a quick look at the prices of components in my local suppler, the 555s will be slightly less expensive than the MCU plus the other required components (driver transistors and voltage regulator) but this will be cancelled out by the extra passive components which aren't required and the PCB being one quarter of the size.

The main reason for opting for MCUs is more to do with time and effort, even if you ignore the fact that it requires you to learn something new, there's certainly less to go wrong inside one chip than three.

Did you get board of programming? I admit I got a little fed up with it. Apart from he fact that I wasn't the best programmer in the world and that I somehow find working with schematics easier than lines of code, I've finally realised how software simplifies things and that having some experience will make me more employable so I'm getting back into it.

Another thing: regardless of whether you're using an MCU or hardware how are you going to assemble it? You do realise that stripboard won't be suitable because the clearance between the mains and DC parts won't be good enough?

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Yes, you are right. And I am thinking to start with the PICAXE because easier to handle. Maybe, after some practice I become addict of PICAXEs  ;D.

Frankly, now I don't have spare time. This circuit is the electronic module of a project which I will use personally for commercial purpose. I am also considering to use the industrial timers. What do you thing, which choice would be more heavy duty type.

The ready-made version based on induction heater, is very expensive......$25,000+

As for the relays, I plan to install them separately, not on the board.

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I've never used a PICAXE before, from what I've read it's just a PIC with a built-in BASIC interpreter and is not the kind of thing I fancy using personally as it will cost more and requires less learning about PICs which is what I want to do but it might be your best bet.

An industrial timers will probably be more a rugged solution you could also consider a small PLC which will offer more flexibility.

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