Propeller in a car...

jmspaggi

Hi all,

I would like to had some features to my car and I'm planning to use a propeller for that.

What I want to add is:

• Temperature controller (instead of just an on/off fan with warm air);
• OGG (Or mp3 if not available) player;
• Rear alarm (the thing which beep when your bumper is close to the wall);
• RTC with multiple alarms, countdown;
• A display and some buttons to control all of that.

If I found other ideas, I will probably at it [noparse];)[/noparse]

My question now is regarding the power suply. I found 12V in the dash and I want to power my board with that. I need to get 5V (The display) and 3.3V from this 12V.

Can I use an LM317 for that? 12V will be enought. But will it be to much and that will overheat? Also, when I start the car, is there some risk to burn the LM317 and/or the prop?

Is there anything I should worrie about with a project like this one?

Thanks,

JM

max72

I used the 12V from the car with protoboards when playing with GPS, and I used 12V gel batteries on the go with the same protoboard. It works fine as long as you don't use too much power.
Otherwise you need to dissipate the heat generated. The higher it input voltage, the more power goes to heat on the regulator.

For instance in my case a LCD with back light was too much.

A switching regulator works fine with me..

jmspaggi

Hi Max,

What I'm expecting to use is:

A LCD back ligh screen http://www.parallax.com/Store/Accessories/Displays/tabid/159/CategoryID/34/List/0/SortField/0/Level/a/ProductID/51/Default.aspx
• 2 or 3 Digital Thermometer http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/DS1620/List/0/SortField/4/ProductID/84/Default.aspx
• A Breakout Board for VS1053 http://www.sparkfun.com/commerce/product_info.php?products_id=8954
• A card reader
• And maybe a ping.
  
  So you said the screen was too much, which mean it will be the same issue for me.
  
  What do you mean by "A switching regulator"?
  
  Thanks,
  
  JM

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Linux? There is worst, but it's more expensive.

max72

Linear regulators have an efficiency inversely related to the voltage drop from supply voltage to regulated voltage, and of course proportional to the current draw.
So heat to be dissipated is proportional to voltage drop and current. The protoboard dissipates heat on the pcb. If you add in your design a heat sink it could be enough and happily live with the linear regulator.

Swhitching regulators are (in general) a more efficient solution.
For instance I use linear's LM2594. You need more external components.

Check the net. The manufacturers usually have designer's guides available for free.

For instance:
focus.ti.com/lit/an/slva118/slva118.pdf

Massimo

max72

Check also this other one:

www.onsemi.com/pub_link/Collateral/HB206-D.PDF

Massimo

jmspaggi

Super, thanks.

Based on my knowledge with electronic components, I will probably go with a heat sink first [noparse];)[/noparse]

And thanks a lot for the links! I will start to read the 1 document you sent. I might be able to get something from that.

JM

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Linux? There is worst, but it's more expensive.

max72

Check also the stability of your supply. For instance when switching on the engine there could be a voltage drop, or the power could be shut down for a little bit, resetting your system. If you cannot accept it you must investigate a temporary supply to the key components. Maybe a supercap is enough...

Have fun!

Massimo

DynamoBen

I used this on a motorcycle project, you could add the 3.3V regulator to it.

www.seetron.com/an_vpwr1.htm

jmspaggi

Can I use this 5V output on the LM317 input to generate the 3.3V? Or will the LM317 require more than 5V do to 3.3V?

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Linux? There is worst, but it's more expensive.

soshimo

jmspaggi said...
Can I use this 5V output on the LM317 input to generate the 3.3V? Or will the LM317 require more than 5V do to 3.3V?

You usually want to keep your supplies separate. Heavy current pull on the LM317 can pull down the voltage down which will cause problems with your 3.3 regulator. Also, if your 317 goes out all your power goes out. If you keep your supplies independent you can avoid all of these issues.

jmspaggi

Ok. Thanks for the recommandation. So I will keep my +3.3 and my +5V. I will probably go with the LM317 because I know it, and put a common heat sink for the 2.

JM

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Linux? There is worst, but it's more expensive.

Jim Fouch

You may want to take a peek at these...· http://www.ereshop.com/index.php?main_page=product_info&cPath=75&products_id=189

They are a switching powersupply that will be much better than a linear one. It has a fixed 5V and an adjustable one.

I'd bypass the linear ones on the proto board and drive it and what ever else you need from this. It will deliver upto 1amp on each the 5V and the adjustable one. I'd replace the pot with a fixed resistor.

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Jim Fouch

FOUCH SOFTWARE

jmspaggi

Looks good! I like solutions where everything is already done for me! [noparse];)[/noparse]

I will see what's the best option for my needs.

Thanks again.

JM

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Linux? There is worst, but it's more expensive.

w8an

Wow, it's hard to justify making any kind of power supply when you can get that SW5AS for fifteen bucks!