Y
Yvan
- Jan 1, 1970
- 0
Hi,
I'm designing an analog input that will accept any external sensor to
our device. I want to be able to support 0-3V, 0-5V, 0-10V and 0-12V.
-I only have access to a 3V regulated voltage supply on the PCB.
-I'm using the 12-bit ADC on the Msp430x1612 microcontroller.
-I'm trying to assume I don't know the output impedance of the
connected sensor
My current strategy would be to have a voltage divider in front of a
voltage follower.
However, the output impedance can vary very much (I'm assuming from 0
to 50 kohm). I don't see how I can have an effective voltage divider
that will give me an error less than 1 LSB unless I use resitors of the
order of 1000 Mohm.
I'm thinking of several solutions:
1)Changing the resistor values to accommodate each using depending on
the sensor. I don't think this is very practical in terms of
assembly management.
2)I could use a potentiometer in order to trim the voltage divider
depending on the sensor.
3)I could give myself headroom assuming a maximum impedance of let's
say 50 kohm - 2.5V. When the impendance is lower the maximum voltage
would drop. It would be up to the user to adjust the range in
software. This solution is very practical in terms of hardware but it
diminishes the range and hence the resolution.
Any other solution to propose? I'm sure there's a fundamental strategy
that is much more effective.
Thank you very much.
Yvan
Newtrax Technologies
www.newtraxtech.com
I'm designing an analog input that will accept any external sensor to
our device. I want to be able to support 0-3V, 0-5V, 0-10V and 0-12V.
-I only have access to a 3V regulated voltage supply on the PCB.
-I'm using the 12-bit ADC on the Msp430x1612 microcontroller.
-I'm trying to assume I don't know the output impedance of the
connected sensor
My current strategy would be to have a voltage divider in front of a
voltage follower.
However, the output impedance can vary very much (I'm assuming from 0
to 50 kohm). I don't see how I can have an effective voltage divider
that will give me an error less than 1 LSB unless I use resitors of the
order of 1000 Mohm.
I'm thinking of several solutions:
1)Changing the resistor values to accommodate each using depending on
the sensor. I don't think this is very practical in terms of
assembly management.
2)I could use a potentiometer in order to trim the voltage divider
depending on the sensor.
3)I could give myself headroom assuming a maximum impedance of let's
say 50 kohm - 2.5V. When the impendance is lower the maximum voltage
would drop. It would be up to the user to adjust the range in
software. This solution is very practical in terms of hardware but it
diminishes the range and hence the resolution.
Any other solution to propose? I'm sure there's a fundamental strategy
that is much more effective.
Thank you very much.
Yvan
Newtrax Technologies
www.newtraxtech.com