18F46K20 Input voltage & ADC

[deperkin]

I am thinking about using an 18F46k20 microchip.
This is a low voltage pic, and it does mention that the voltage on any pin is to be
-0.3V to (VDD + 0.3V). I would plan on using a 3.3V power supply for this application.
I also have a MPXV7002GP pressure sensor I would like to use.
The output voltage on this is from 0.5 to 4.5V, which seems to be to be a problem with this PIC.

I admit I have not completely read through the datasheet for the PIC yet however.

I also have not been able to find an alternate pressure sensor.

I would imagine this is a common question for this PIC, although nothing I saw in searches suggested this.... What is the best way to use sensors, ADC or TTL that have 5V outputs? I need to be accurate on the pressure sensor and do not see using a resistor in this case the correct way to approch it...

 

[jalonso]

Hi,

Using a voltage divider is not a bad approach...
You can use 1% resistors to "scale down" the output voltage of the pressure sensor.

Regards.

 

[millwood]

This is a low voltage pic, and it does mention that the voltage on any pin is to be
-0.3V to (VDD + 0.3V). I would plan on using a 3.3V power supply for this application.
I also have a MPXV7002GP pressure sensor I would like to use.
The output voltage on this is from 0.5 to 4.5V, which seems to be to be a problem with this PIC.

I would double check the datasheet to make sure that you are doing an apple-to-apple comparison here. most of the mcus today have 5v-compliant io pins - they are clamped.

I admit I have not completely read through the datasheet for the PIC yet however.

that would be your first order of business.

I would imagine this is a common question for this PIC, although nothing I saw in searches suggested this.... What is the best way to use sensors, ADC or TTL that have 5V outputs? I need to be accurate on the pressure sensor and do not see using a resistor in this case the correct way to approch it...

many possible approaches. you can for example ignore it if you don't need to measure full range; you can step it down via a resistor divider - though you need to be careful about the output impedance of such a network. you can use a 5v adc, you can buffer it with an opamp and scale the input signal down to 3.3v, etc.

each solution will depend on many factors that you did not outline.