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Analog

There are a number of functions that start a simple analog sensor server. We'll use startPotentiometer() as an example, but you can use any of the following, as they all use the same configuration.

In the simplest case, you just pass the pin to startPotentiometer(). The voltage on the pin (typically between 0V (GND) and 3.3V (VCC)) will be translated to a number between 0 and 1.

import { gpio } from "@devicescript/core"
import { startPotentiometer } from "@devicescript/servers"

const slider = startPotentiometer({
    pin: ds.gpio(3),
})
slider.reading.subscribe(v => console.data({ value: 100 * v }))

Scaling​

There are two settings, offset and scale that let you modify the value read from the sensor. The actual reported reading is (offset + (raw_reading * scale) / 1024) / 0xffff clamped to 0 ... 1 range. The range of raw_reading is 0 ... 0xffff. The defaults are { offset: 0, scale: 1024 } so the raw_reading is just reported back.

For example, if you find you can never quite reach the 0 and 1 values, you can try the following:

import { gpio } from "@devicescript/core"
import { startPotentiometer } from "@devicescript/servers"

const slider = startPotentiometer({
    pin: ds.gpio(3),
    offset: 0x1000,
    scale: 900,
})

Limiting power consumption​

A potentiometer typically has 3 terminals, let's call them L, M, R. You connect L to GND, R to VCC and M (middle) to the sensing pin. The M terminal will then get a voltage proportional to the position of the knob.

However, the current (0.3mA with typical 10kOhm potentiometer) will always flow from L to R, regardless if you measure it or not. To improve power consumption, you may connect say R to a GPIO and configure the service like this:

import { gpio } from "@devicescript/core"
import { startPotentiometer } from "@devicescript/servers"

const slider = startPotentiometer({
    pin: ds.gpio(3),
    pinHigh: ds.gpio(7),
})

This tells the driver to set GPIO7 (pinHigh) to 1 (3.3V) before taking the measurement from GPIO3 (pin). After taking the measurement, pinHigh will be left floating, so no current will flow through the potentiometer.

You can also set pinLow (which is set to 0 before taking measurement) or both pinHigh and pinLow, but typically one is enough.

Timings​

The samplingItv settings defaults to 9 milliseconds and specifies how often to sample the sensor.

The streamingItv setting defaults to 100 milliseconds and specifies how often to stream values on the Jacdac bus. The client can override this through streaming_interval Jacdac register.

Additionally, you can set samplingDelay to a number of milliseconds to wait after setting pinHigh/pinLow before taking the measurement (default is 0, so effectively a few microseconds (not milliseconds)).