ZIO, Motherboard User Manual
Rev. 2.0
Zilogic Systems
Page 14
To better understand the operation of the circuit, the circuit is shown with the internal pull-up
resistor on the
Sensor
signal, in the following diagram.
Using superposition, the voltage at
Sensor 0
is given by the following formula.
Voltage at
Sensor 0
= 1.5V + V
i
/ 2
As V
i
decreases from 3V to -3V, the voltage at the
Sensor 0
decreases linearly from 3V to 0V, and
the raw value from 0xFFFF to 0.
V
i
(V)
Voltage at
Sensor 0
(V)
Raw Value
3
3
0xFFFF
0
1.5
0x7FFF
-3
0
0
Voltage measurement, -15V to +15V.
The following circuit can be used to measure voltages
in the range -15V to +15V. The input voltages and the corresponding raw values is shown in the
table below.
V
i
(V)
Voltage at
Sensor 0
(V)
Raw Value
15
3.0
0xFFFF
0
1.5
0x7FFF
-15
0.0
0
4.3. Non-resistive Sensors
Transistor Buffer.
Non-resistive sensors usually generate a voltage signal that varies with the
parameter being measured. Such sensors cannot be directly connected to the
Sensor N
signal,
due the signal being pulled-up to 3V using a 10K resistor. A transistor buffer can be used to
overcome this problem. The transistor isolates the sensor from the pull-up. A transistor buffer
circuit is shown below.
