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Tobias
12-03-2006, 11:49 PM
can I power the board of education with my 12 volt power supply which is really 13.8 volts?

Mike Green
12-04-2006, 01:06 AM
The voltage will not harm the BOE, but will severely limit what you can power from the regulator on the BOE. The regulator has to dissipate as heat the power from the voltage drop from 13.8V to 5V (=8.8V). It will protect itself from overheating, but this will limit the current it can supply. The recommendation is to use no higher than a 9V supply.

Tobias
12-04-2006, 01:38 AM
could i just place a resistor whatever value? into to the +power source because my project will only have a 12 volt power source?
-Tobias

PJ Allen
12-04-2006, 01:55 AM
It's the magic Rwhatever.· http://forums.parallax.com/images/smilies/rolleyes.gif· Why don't you try that and see?

[ Mike gave you a good, detailed·answer.]

allanlane5
12-04-2006, 04:49 AM
The "Linear Regulator" on the BOE board acts itself as a variable resistor, which drops just enough voltage so its output is always +5 volts. Thus, it dissapates the 'extra' voltage as heat.

So, 13.8 volts - 5 volts == 8.8 volts, that the regulator has to disappate. Power == Current * Voltage.

So, if you pull 100 mA through the regulator, it's disappating 100 mA * 8.8 Volts == 0.88 watts. I believe without heat-sinking, the regulator can disappate about 1.5 watts. So you should be OK.

The regulator disappates power by heating up and letting the ambient air draw off the extra heat. At 0.88 watts, it might get a little warm. If it gets too hot, it has a built-in Thermal Shutdown circuit which will cut off the current if it DOES get too warm.

If you add another resistor to the circuit, you'll need to heat-sink that resistor -- Linear Regulators are designed to disappate the heat.

allanlane5
12-05-2006, 09:40 PM
Because if you change out the BOE's regulator from 5 volts to an 8 volt one, you'll be applying 8 volts to the VDD line, which WILL destroy the BS2.

Chris Savage
12-05-2006, 10:53 PM
Hello,
·
·· 8V does fall between the 5.5V to 15V range, however VIN on the board is fed directly to the BASIC Stamp VIN.· Changing the regulator on the board will not affect this at all.· It will only affect what is going to the VDD connections on the board.· This does not affect VDD on the BASIC Stamp since that is not connected to the output of the TO-220 regulator on the BOE.· I hope this helps.· Take care.

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Chris Savage
Parallax Tech Support

Chris Savage
12-06-2006, 01:42 AM
Can you post the schematic you have?· The only difference I recall in any BOE Schematic was whether or not VDD from the Stamp Module went to the AppMod socket.

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Chris Savage
Parallax Tech Support

Chris Savage
12-06-2006, 03:28 AM
As I suspected…You’re looking at Rev A. schematics for a board we haven’t sold in a long time.· The most up to date schematics are always on our website.· Please check the link below.· You will also find that the·current board·does have the two VDD circuits labeled differently.· I will see the next schematic revision shows this as well.

http://www.parallax.com/dl/docs/prod/boards/BOERevC.pdf

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Chris Savage
Parallax Tech Support

allanlane5
12-06-2006, 09:57 PM
There are none so ignorant as those who will not learn. Whatever, dude.

Tobias
12-06-2006, 11:41 PM
Is it ok for me to power the BS2 with 12v and just use the 5v for my inputs?

Chris Savage
12-06-2006, 11:46 PM
Tobias,
·
·· If you connect the 12V to VIN then yes, you can do this.

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Chris Savage
Parallax Tech Support