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Author Topic: £$£ HELP! £$£  (Read 3753 times)

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Ratsil

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£$£ HELP! £$£
« on: February 25, 2009, 16:44:53 PM »
I have been asked to do an assignment towards my National Certificate and could really do with a hand.

Q) You have recently been recruited as a junior design engineer with a local company that specializes in temperature control applications. One of your first tasks is to design a solution that will maintain the temperature of a living space with a volume of 400m3 (cubed) between 25-30 degrees centigrade?

You are allowed to use the following components as a part of your design.

LM35 Temperature sensor
LM358 Operational Amplifier
3 x LM311 Comparartors
74LS32 Quad or Gate
74LS04 Hex NOT gate
2 x 12 volt relays



If you could help me with my assignment i am willing to pay a maximum of £100 as i am only a student with sufficent funds

Thanks

stuadd@yahoo.com

kam

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Re: £$£ HELP! £$£
« Reply #1 on: February 25, 2009, 16:53:18 PM »
Welcome Ratsil, it is nice to have you in our company here!

Your question confuses me a little bit. You've been given the volume (400m3), that COULD mean that they need some calculations on the speed of heating (efficiency). Or not? Because you could only calculate it when you have some more information on the heating agent.

It could also be only some tricky part of the question. In this case, your task is to make a temperature sensor. Is this true? If yes, it does ot look like a difficult task and we could take care. How much time do you have?


P.S. You need to pay nothing in PCB heaven. Do not forget to visit us again in a few weeks (2-3 weeks from now) where the new PCB heaven will be uploaded and running. That would be for us your best support ;)

Ratsil

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Re: £$£ HELP! £$£
« Reply #2 on: February 25, 2009, 23:20:48 PM »
Basically this is all i have been given...
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You have recently been recruited as a junior design engineer with a local company that specializes in temperature control applications. One of your first tasks is to design a solution that will maintain the temperature of a living space with a volume of 400m3 (cubed) between 25-30 degrees centigrade?

You are allowed to use the following components as a part of your design.

LM35 Temperature sensor
LM358 Operational Amplifier
3 x LM311 Comparartors
74LS32 Quad or Gate
74LS04 Hex NOT gate
2 x 12 volt relays

For this task you will need to obtain all of the relevant data sheets and make use of every source of data available. You should keep full records of any correspondents you make and include this as part of a project portfolio which should be submitted as evidence towards the given outcomes. Your portfolio should also include the following evidence as a minimum.

A block diagram of the project
Schematics based on each design phase
A full schematic of the completed design
A Gantt Chart for porject planning
A target sheet detailing your weekly targets
A project diary
A finalized cost for the finished product
Details of the heating and cooling solution you have chosen along with a full evaluation

Remember Design is often done in small stages. You should keep full records of all your notes.

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I have 2 weeks basically till i hand it in and could really do with all the help i can get

Thanks alot

kam

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Re: £$£ HELP! £$£
« Reply #3 on: February 26, 2009, 18:06:48 PM »
One last question. You need to control the temp how? For example,

1. you need to cool the room if temp >=30 down to 25?
2. you need to heat the room if temp <=25 up to 30?

or

3. You need to do both 1 and 2 to keep the room in 27.5 degrees?

Looking your component stock, i would say that you go for no3, because no1 and 2 requires only 2 comparators. 3 requires 3.

Ratsil

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Re: £$£ HELP! £$£
« Reply #4 on: February 27, 2009, 13:16:06 PM »
to be honest im not 100% sure where to start i think the assignment given is really poorly wrote and dosent actually explain what we have to do... I have found all the data sheets needed for the components its just where do i go from there? The block diagram is really confusing as i dont know where to start or what it is for...

Thanks for this really appreiciated

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kam

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Re: £$£ HELP! £$£
« Reply #5 on: February 28, 2009, 10:28:22 AM »
Oh ok, I see.

Well, i suggest a cooling/heating system. That should be also why you have 2 relays. One for the heater and one for the cooler. So...

In the first attachmenet you find the 'how to' connect the sensor to the op-amp. At the output you have a nice clear signal to play with at the next stage. This is the first stage.

The next stage is the comparator. You need 3 comparators. One will operate from 30 and higher and actuate the cooler relay.
The other will operate from 25 and lower and will operate the heater
The last will monitor the 27.5 degrees. If the temp is 27.5, then all relays will stop operating (heater and cooler will stop operating).

In the second attachment you can find a typical connection for the comparators you have. The resistors values are typical and you may need to alter them somehow to fit your needs. From pin 2 you connect the output of the previous stage. You need 3 of these comparators.

Now, as for the operatioon, you need to have some flip flops to do this. See the next attachmenet. You can make flip flops with nor gates (or gates with a not conected to its output). So you make 2 flip flops. The first to be actuated from the high temp comparator and the next from thelow temp. Both of them will be reset from the middle temp comparator. The ouputs of those flip flops will actuate the relays.

Note that the relays require a mid stage to drive them. This driver is seen on the next attachment.

As you understand, you need to put them to the lab. I suggest you get a breadboard and make it work.

Good luck! And do not forget to visit us an a few weeks for the new PCB Heaven!
And when you get the results, please inform us fom the results!