Re: Battery supplied PIC and A/D

[Vernon]

Can anyone suggest how to generate a stable reference on a
battery operated PIC system? Don't want the ref changing as
the battery discharges.
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[John Kennedy]

:= Can anyone suggest how to generate a stable reference on a
:=battery operated PIC system? Don't want the ref changing as
:=the battery discharges.

Depends on the accuracy you need for the ref. A cheap version I would use the TL431 shunt regulator this will give a 2.5V reference at 2\% accuracy. If you need a lower voltage or greater accuracy then you can buy precision reference devices of varying voltages.

A resistor would be needed between the reference device and the battery supply to limit the current flow through it.

Hope this helps

JFK
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Original Post ID: 998

[Neutone]

:= Can anyone suggest how to generate a stable reference on a
:=battery operated PIC system? Don't want the ref changing as
:=the battery discharges.


Linear has a good selection and you can order direct.
<a href="http://www.linear.com/" TARGET="_blank">http://www.linear.com/</a>
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Original Post ID: 999

[Sherpa Doug]

One nice chip is the MAX187. It is an A/D that runs off the +5v supply and gives you its 4.096V reference to drive your sensor.

Sherpa Doug

:=:= Can anyone suggest how to generate a stable reference on a
:=:=battery operated PIC system? Don't want the ref changing as
:=:=the battery discharges.
:=
:=
:=Linear has a good selection and you can order direct.
:= <a href="http://www.linear.com/" TARGET="_blank"> <a href="http://www.linear.com/" TARGET="_blank">http://www.linear.com/</a></a>
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Original Post ID: 1005

[Bob Lin]

:= Can anyone suggest how to generate a stable reference on a
:=battery operated PIC system? Don't want the ref changing as
:=the battery discharges.
If battery supplyied PIC .That's Vcc between 3V to 5V.
TL431 is very cheap about USD 10 cents.
I using Vcc=Vref mode.
Connect is vcc..>resistor ..>AN0..>TL431..>GND
Tl431 is 2.5V.
So AN0=2.5V
Analog input range from 0 to Vcc.
example 1 (PIC16F877 10 bit A/D)
If a/d convert result from pin AN0 is 512 . I get Vcc=5V.
{1 LSB=2.5V/512=4.88 mV.Full scale(Vcc)=4.88mV*1024=5V}
If AN1 pin input result = 800 .I get AN1=3.906V.
{ 4.88mV * 800 =3.906V}
example 2
If a/d convert result form pin AN0 is 700. I get vcc=3.657V.
{ LSB=2.5V/700=3.57mV. Vcc=3.57mV *1024 =3.657V)
If AN1 pin input result = 800 .I get AN1=2.857V.
{ 3.57mV * 800 =2.857V}

Above is very useful for everyone.
BoB Lin (Taiwan)
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