ADC help

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admin
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Posted by admin: Sat. Mar 10, 2001 - 08:12 AM
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I want to hook up my 90S8515 to a ADC0804 and messure a 24 volt battery. the input of the ADC is only 5 volts.. how do i messure a 24v battery with this combination? can it be done?
any examples? Please ive searched for this info and am stuck. Tks in advance. Dan.

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AVR Microcontrollers, megaAVR and tinyAVR, AT90S8515
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admin
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Posted by admin: Sat. Mar 10, 2001 - 02:44 PM
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Dan,

You need to use a voltage divider.
R1 R2
+24V----VVVVVV---|---VVVVVVV--Gnd
|
ADC
ADC voltage = 24V * R2/(R1+R2) , the 24V is actual battery voltage.
You may want to design in some over-range with 30V divided down to 5V.
R1 = 50K, R2 = 10K
The use of a AT90S8535 with an internal A/D may be more cost effective.
It has a very high input impedance that will not require an input buffer.

Dave

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admin
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Posted by admin: Sat. Mar 10, 2001 - 02:55 PM
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In the above note the ADC input should be connected at the junction between the resistors.
Leading spaces were deleted in the post.

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Dibor
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Posted by Dibor: Mon. Mar 12, 2001 - 03:06 PM
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Connect 24V through resistor divider to input ADC.

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