ADC question

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AtomSoft

Well-Known Member
Hey guys im not a noob when it comes to takin in samples from ADC but i wanted to know... can we use ADC to calc battery voltage like...

Lets say my battery is a 3.6v and it drops to 3v...

How do i still use that 3.6v from before ? Like if i use my main power *Battery* as the VREF then it will always show 100% since its the refrence... How to i check level against power that isnt there?

Anyway the basic question is how to use ADC for battery monitor?
 
Some microcontrollers have an internal reference, like the MSP430 has a 2.5V internal reference. If that's not the case, if you are using a regulator, you can sample the actual battery voltage through a voltage divider and use your voltage after the regulator as the reference. Otherwise you will need to buy a reference voltage IC to supply VREF with a reduced stable voltage.
 
hi atom,
Instead of using the PIC's internal +Vref as you are doing at the present, you select one of the adc pins as +Vref in, use a 2.52Vref IC... not expensive.
EDIT: or a 1.25V ref
 
Last edited:
Thanks for the info. Can someone supply me with a sample of a VREF IC? How do they work? Do they simple take a input and supply the output with low current?
 
AtomSoft said:
Thanks for the info. Can someone supply me with a sample of a VREF IC? How do they work? Do they simple take a input and supply the output with low current?
Click to expand...

hi atom,
Look at this.

EDIT.
added pdf
 

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How do you think i should monitor the battery.. since im using ADC. Using a VREF IC .. if i use a 3.3v VREF will it drop below 3.3v is the battery is less than 3.3v? Is that why you are posting a 1.2v vref? how would i check if its 2.8v using a 1.2v? i see its 1/3 of the battery... is it simply just multiply my results?
 

hi,
Its just a little maths if you want the actual battery voltage or a compare voltage if less than 'do something'
 
Digikey is the cheapest with QTY of 1 heh...

Ill buy about 3-6 of them tho...

**broken link removed**
 
HOLY MOLY LOL look:
**broken link removed**

Even tho i read on Micrel:

***PRODUCTS BELOW ARE OBSOLETE***
***NOT RECOMMENDED FOR NEW DESIGNS***

LM4040AIM3-2.5
LM4040BIM3-2.5
LM4040AIM3-4.1
LM4040BIM3-4.1
LM4040AIM3-5.0
LM4040BIM3-5.0
LM4041AIM3-1.2
LM4041BIM3-1.2
Click to expand...

$4 (USD) for 50 pcs is nice!!! Thats $0.08 (USD) each
 
Last edited:
E-Bay link looks really good.

The Micrel obsolete part numbers aren't available to buy, so it doesn't really mean anything to us.
 
hi atom,
This a 2.5V option, quite cheap.
 

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