Flex+Sensors

[desmomito]

Hi all,
I have two questions about connecting sensors to the Flex-Full Board.

1) I have a sensor which has got an output 0-5V. Which is the best way to connect it to the Flex which has got the Vref levels 0-3.3V ?

2) I have another sensor which has three pins +12V, OUT (0-5V), GND. From the Flex I have only the possibility to have 3.3V or 5V as output power supply. If I use an external power supply for the sensor I think I\'ll lose the ground reference and than I won\'t have a correct measure from the sensor ? How could I solve it ?

Thanks in advance,
Pasquale.

[paolo.gai]

Hi Pasquale!

About the following one:

1) I have a sensor which has got an output 0-5V. Which is the best way to connect it to the Flex which has got the Vref levels 0-3.3V ?

check the pins you want to connect on the dspic datasheet. Most of the dsPIC pins accept a 5V input...

ciao,

PJ

[desmomito]

Hi,
I\'ve checked. The problem is the only digital input pins can accept 5V. Unfortunatly not analog input pins.


Any order informatiot about my post ?


Thank you,
Pasquale.

[nino]

You\'re right, analog inputs accept only voltages in the 0-3V3 range.

The faster solution is a couple of resistors in order to do a partition. Better solutions are possible with buffers, OA with gain set to 2/3 and so on... It depends from your sensor.

[desmomito]

Thank you very much. What about the second one :

2) I have another sensor which has three pins +12V, OUT (0-5V), GND. From the Flex I have only the possibility to have 3.3V or 5V as output power supply. If I use an external power supply for the sensor I think I\'ll lose the ground reference and than I won\'t have a correct measure from the sensor ?

[nino]

You have 2 possibilities:

[ol]
[*]You use an external 12V power supply and connect the 2 Ground.
[*]You power the Flex board with a 12V supply and use the Vout line for the sensor power supply.
[/ol]

Thr first one is better in term of quality, while the second one is easier because it uses only 1 powre supply.

[desmomito]

Thank you for your advices. I have one more question :

- What\'s the difference between GND_OUT and GND ? I\'m using for the sensors which needs power supply 3.3V and 5V the GND as ground reference. For the sensor which needs 12V if I use the second method that you\'ve written : Could I use the Vout and GND or I have to use V_OUT and GND_OUT ? Will I loose something because the references af the ADC are 3.3V and GND ?


Thank you in advance,
Pasquale.