FlexCase
Analog Input Guide
Analog Input Specifications
| Feature | Specification |
|---|---|
| Maximum Input Voltage | 36V |
| Default Pull | Pull down |
| Resolution | 8, 10, 12, 14* bit |
| Cutoff Frequency | Coming soon. |
| Reading Precision | 0.25% |
| Capacitance | 455 pF |
| Protections | Overvoltage, Reverse Polarity |
*Only available on some models.
Analog Circuit Details
The standard SKUs have a voltage divider of 1/12th, so a 36V input will reach the MCU at 3.0V.
The equation to calculate theoretical ticks is
ADC ticks = (Resolution of ADC/3300 mV) * (Input voltage mV) * (Divider Ratio)
A 12V input on the standard input circuit (Divider ratio = 1/12) for different resolutions is calculated as:
| Resolution of ADC | Input Voltage | Read Ticks | Millivolts/tick |
|---|---|---|---|
| 8bit = 255 | 12000 mV | 77 | 155 |
| 10bit = 1,023 | 12000 mV | 310 | 39 |
| 12bit = 4,095 | 12000 mV | 1240 | 9.7 |
| 14bit = 16,383 | 12000 mV | 4964 | 2.4 |
However, there are voltage drops along the sensing line and tolerances with the components, so it is always best to calibrate.
Alternative Configuration Examples
For volume orders, the voltage divider can be modified to order as required. This can be useful for a 0-5V throttle signal to achieve sub 1mV/tick accuracy. Note that the maximum voltage on the line is reduced to the maximum measurement value if changed.
A dual position sensor may commonly have a 0-5V range, load requirements, and capacitance requirements. With two 23K2 resistors the measurement becomes 0.4mV/tick with a 0-6V range and a 15mV precision.
A PT1000 can have a resistance of 800-1600 ohms across a temperature range of -50 to 130C. If the sensor is supplied with the 5V sensor supply and connected to an analog input with R1 configured for 0 ohm and R2 configured for 1000 ohm the following performance is achieved.
At its worst sensitivity (150 C), a 14bit analog read 0.8 degrees C/tick.
Note: It may be important to calibrate the sensor readings.
A NTC 10K can have a resistance of 500-700,000 ohms across a temperature range of -50 to 130C. If the sensor is supplied with the 5V sensor supply and connected to an analog input with R1 configured for 0 ohm and R2 configured for 700 ohm the following performance is achieved.
Note: It may be important to calibrate the sensor readings.
