alternative Pin for vref

[paul borgmeier]

Hi all,

I have a project envolving a 12F675 pic reading a LM35 sensor.
The problem is that i'm using 5V as power and it's too much for the ADC resolution.

Also, i dont have any pin left that i can use for a lower voltage input for vref.

I have as inputs:
One pin for the sensor and one for a button
For outputs i have one pin for 2 leds and one for the serial out.

Also have 2 extra for the external eeprom data ( SCL and SDA ).

Is there a way i can get a better resolution with this setup or do i need more pins ?

The only thing i thought of was to lower the source power to 3V using a voltage divider after the 5V regulator and try to power all ( pic + leds + eeprom ) with 3V.

EDIT: I'm guessing that this way it will not work because it will not have the 5v needed to serial out the data to rs232
.

You mentioned SCL and SDA for the eeprom? Many EEPROMS of this type can run at lower voltages like 1.8V or higher. Check your datasheet (see for example 24LC08 from microchip). Also, these pin names imply Synchronous Serial Data exchange, not RS232.

you should be fine at the lower voltage (provided your EEPEOM can run that low). However the LM35 needs 4 VDC so run the PIC, the LEDs and the EEPROM at 2.5-3V and the LM35 at 5 V. ... I agree with Dave in post #2