/* zapojení AI na Unipi 1.1 */
Analog inputs on Unipi 1.1 serve for reading 0-10 V⎓ voltage or resistance sensors (eg. Pt1000 temperature sensors). For resistance measurements, it is necessary to perform an external adjustment. The negative pole of the measured external device is connected to the **AIx-** terminal of the given connector while the positive pole (signal) is connected to the **AIx+** terminal (**x** represents the input's number).
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Unipi 1.1
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**Analog inputs are available only on Unipi 1.1**
====== Connection ======
The following pictures illustrate connection for measuring a voltage source on terminals **AI2+**, **AI1-**, **AI2+** and **AI2-**.
{{ :en:hw:019_connection_of_io.png?direct |}}
====== Resistance measurement ======
If you need to use the Unipi 1.1 to measure resistance (eg. from Pt1000 temperature sensor), you need to add a resistor between the sensor and the board, as shown on the picture below:
{{ :en:hw:020_connection_of_io.png?direct |}}
12 V⎓ power supply on Unipi 1.1 is designed for digital inputs and can act as float voltage. For accurate readings we recommend using external power supply:
{{ :en:hw:021_connection_of_io.png?direct |}}
**R_sens** = sensor resistance (400 Ω - 5000 Ω) \\
**R_ref** = reference resistor (1.2 kΩ) \\
**R_ai** = AI input resistance = 12.2 kΩ \\
**Vcc** = voltage supplied to the circuit. The image above depicts 12 V⎓ voltage. \\
**V_ai** = measured voltage between **AIx+** and **AIX-**.
At 12 V⎓ voltage and R_sens >= 200Ω, use reference resistance R_ref = 1.2 kΩ. At R_sens < 200 Ω use R_ref = 10 kΩ.
The **R_sens** value of the measured resistance is calculated using voltage measured on the selected analog input:
Vcc - V_ai R_ref * R_ai
R_sens = ------------ * --------------
V_ai R_ref + R_ai
An example of calculating the read resistance: {{files:products:unipi1:unipi_1_resistance_reading.pdf|PDF download}}