Analog In

Analog input pins read a continuous range of voltages instead of just high or low. Each input pin connects internally to an Analog-to-Digital Converter (ADC) that converts the voltage into a digital value.

Microcontrollers running on 3.3V can typically read voltages between 0V and 3.3V. The ADC's resolution determines accuracy:

• SC20xxx — 16-bit ADC (65,536 steps; ~50 µV per step over a 3.3V range)
• SC13xxx — 12-bit ADC (4,096 steps; ~0.8 mV per step over a 3.3V range)

Voltage changes smaller than one step are below the ADC's resolution and won't register.

NuGet packages: GHIElectronics.TinyCLR.Devices.Adc for the API, and GHIElectronics.TinyCLR.Pins for pin name constants.

tip

Channel number ≠ pin number. Use the pin constants from GHIElectronics.TinyCLR.Pins to map a physical pin (like PA0) to its ADC channel — for example, SC20100.Adc.Controller1.PA0.

Reading a value

ReadRatio() returns a normalized double from 0.0 to 1.0; ReadValue() returns the raw integer (range depends on resolution).

using GHIElectronics.TinyCLR.Devices.Adc;
using GHIElectronics.TinyCLR.Pins;
using System.Diagnostics;
using System.Threading;

var adc = AdcController.FromName(FEZBit.Adc.Controller3.Id);
var analog = adc.OpenChannel(FEZBit.Adc.Controller3.P0);

while (true){
    double ratio = analog.ReadRatio();
    Debug.WriteLine("An-> " + ratio.ToString("N2"));
    Thread.Sleep(100);
}

Sampling time

The ADC takes a small but non-zero amount of time to settle on each conversion. Longer sampling times improve accuracy on high-impedance signals at the cost of throughput. Default is 1 tick (one tick = 100 ns).

adcChannel.SamplingTime = TimeSpan.FromTicks(10); // ~1 µs

If the requested time falls between two supported values, the higher (slower) one is used.

SC20xxx (full or half speed):

Ticks	Time
0	23 ns
1	132 ns
2	257 ns
5	507 ns
10	1.0 µs
60	6.1 µs
126	12.7 µs

SC13xxx (full speed):

Ticks	Time
0	81 ns
1	156 ns
3	306 ns
5	593 ns
11	1.2 µs
30	3.1 µs
80	8.0 µs

SC13xxx (half speed):

Ticks	Time
1	162 ns
3	312 ns
6	612 ns
11	1.2 µs
23	2.3 µs
60	6.2 µs
160	16.0 µs

Internal temperature sensor

SITCore chipsets include an internal temperature sensor on a dedicated ADC channel. Calibration values are stored in chip-specific memory regions and read with Marshal.ReadInt32.

using System;
using System.Threading;
using System.Diagnostics;
using System.Runtime.InteropServices;
using GHIElectronics.TinyCLR.Devices.Adc;
using GHIElectronics.TinyCLR.Native;
using GHIElectronics.TinyCLR.Pins;

var sc20xxx = DeviceInformation.DeviceName.IndexOf("SC20") >= 0;

var ts_reg1 = sc20xxx ? (IntPtr)0x1FF1E820 : (IntPtr)0x1FFF75A8;
var ts_reg2 = sc20xxx ? (IntPtr)0x1FF1E840 : (IntPtr)0x1FFF75CA;
var enable_reg = sc20xxx
    ? (IntPtr)(0x40000000U + 0x18020000 + 0x6300 + 8)
    : (IntPtr)(0x40000000U + 0x08000000U + 0x08040300U + 8);

var controller = sc20xxx
    ? AdcController.FromName(SC20100.Adc.Controller3.Id)
    : AdcController.FromName(SC13048.Adc.Controller1.Id);

var channel = sc20xxx
    ? controller.OpenChannel(SC20100.Adc.Controller3.InternalTemperatureSensor)
    : controller.OpenChannel(SC13048.Adc.Controller1.InternalTemperatureSensor);

var enable_val = Marshal.ReadInt32(enable_reg);
enable_val |= (1 << 23);
Marshal.WriteInt32(enable_reg, enable_val);

while (true) {
    var v = channel.ReadValue() * 1.0;

    var ts1 = Marshal.ReadInt32(ts_reg1);
    var ts2 = Marshal.ReadInt32(ts_reg2);

    if (!sc20xxx) {
        ts1 &= 0xFFFF;
        ts2 &= 0xFFFF;
        v *= 1.1;
    }

    var t1 = (110 - 30) * 1.0;
    var t2 = (ts2 - ts1) * 1.0;
    var t3 = (v - ts1) * 1.0;

    var temperature = t1 / t2 * t3 + 30;

    Debug.WriteLine("T = " + temperature + " Celsius");

    Thread.Sleep(1000);
}

API reference

Namespace	Description
GHIElectronics.TinyCLR.Devices.Adc	ADC controller and channel classes