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Electronics => Electronics => Topic started by: HDL_CinC_Dragon on July 12, 2007, 04:29:44 PM

Title: Reading 4.21v from my 5vreg
Post by: HDL_CinC_Dragon on July 12, 2007, 04:29:44 PM

My current setup allows me to connect a USB cable to my $50 photovores mobo to power it up. I have the negative to the negative, positive to the positive. When I get the voltage reading off the USB cable directly, it reads 5.15v. When I get the voltage reading between ground and the regulated side of my vreg, it shows 4.21v. 4.21v is not enough to run the AT Mega8 right? When I hook up my 6v battery pack and get the regulated reading from my vreg, its 4.55v. That is also not enough to run the At Mega8 correct?


If im not mistaken, the lowest "high" or "1" voltage for square waves is 4.85v, right? and the highest "low" or "0" voltage is .15v? Am I remembering that correctly? And everything else is read as an error?


Does this mean I should replace my vreg?


In the mean time im just going to hook the USBs positive directly to the VCC pin since USBs are already 5v regulated

Title: Re: Reading 4.21v from my 5vreg
Post by: Steve Joblin on July 12, 2007, 04:35:27 PM

Can you tell us the make and model of your voltage regulator?  When you say you've tried hooking it up to your 6v battery pack, what is the voltage coming out of the battery pack?  I ask this because your battery pack may not be supplying 6v!

Most voltage regulators require a minimum voltage to guarantee a consistent output voltage... you may not be supplying it with enough voltage for it to regulate properly.

Although it is not the cause of the problem, please let us know what size and type filter caps you are using on the input and output side.

Title: Re: Reading 4.21v from my 5vreg
Post by: brijesh on July 12, 2007, 10:47:40 PM

Generally,
The lowest "high" is 2.0V
The highest "low" is 0.8V.

From the ATMega8 datasheet....
Operating Voltages
2.7 - 5.5V (ATmega8L)
4.5 - 5.5V (ATmega8)

Steve,
I saw your website and the pics of SonarBot and Mybot, what did you use as wheels? Cool idea :-)

Title: Re: Reading 4.21v from my 5vreg
Post by: HDL_CinC_Dragon on July 12, 2007, 11:09:00 PM

KA7805 is the serial
its rated for 5v, 1A with a 4% tolerance

Also on the same side as the serial it reads:
E      H06

Title: Re: Reading 4.21v from my 5vreg
Post by: Ro-Bot-X on July 13, 2007, 02:51:12 AM

As far as I know, 7805 needs 7.2 volts to provide 5 volts regulated. If you are supplying 6v you will need a Low Drop-out regulator like LM2940.

Title: Re: Reading 4.21v from my 5vreg
Post by: HDL_CinC_Dragon on July 13, 2007, 08:15:21 PM

but... but.... damn lol


well at least for now I can use the USB cable ive hooked up to it for its 5 volts of regulated googness (about 5.15 volt reading on my DMM)


Thanks for the help