> ## Documentation Index
> Fetch the complete documentation index at: https://instro.nominal.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Using instro

> Using instro with some more detail

This page discusses details about using `instro`.

## Instruments

### Two ways to get data

You can acquire measurements from an instrument in two ways.  The difference is who triggers the reads and how often.

|              | Background acquisition                                                                                                                                         | On-demand acquisition                                                                                   |
| ------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------- |
| **How**      | Call `start()`. A background daemon reads from the instrument at a fixed, configurable rate. Pull the latest N values with `get_channel()` when you need them. | Call read methods (`read_analog()`, `get_voltage()`, …) only when you want a measurement.               |
| **Best for** | Apps where data should always be available and publishing.                                                                                                     | Apps that need measurements only at specific times; lower system and bus load. DMMs are a good example. |

## open()/close() or `with` block

Instruments can also be open/closed automatically using a `with` block.

<Tabs>
  <Tab title="Explicit open() / close()">
    Best when the instrument's lifetime spans many functions, or when you want to interleave setup and teardown across event handlers, fixtures, or REPL sessions.

    ```python theme={null}
    from instro.psu import InstroPSU
    from instro.psu.drivers import SimulatedPSU

    psu = InstroPSU(
        name="bench_psu",
        driver=SimulatedPSU("TCPIP0::127.0.0.1::5025::SOCKET"),
        num_channels=2,
    )
    psu.open()

    psu.set_voltage(5.0, channel=1)
    psu.set_current_limit(1.0, channel=1)
    psu.output_enable(True, channel=1)

    voltage = psu.get_voltage(channel=1)
    print(f"V: {voltage.latest:.3f} V")

    psu.output_enable(False, channel=1)
    psu.close()
    ```
  </Tab>

  <Tab title="with block">
    Best for scripts and tests where the instrument is used inside a single scope. `close()` runs automatically on the way out, even if an exception is raised.

    ```python theme={null}
    from instro.psu import InstroPSU
    from instro.psu.drivers import SimulatedPSU

    with InstroPSU(
        name="bench_psu",
        driver=SimulatedPSU("TCPIP0::127.0.0.1::5025::SOCKET"),
        num_channels=2,
    ) as psu:
        psu.set_voltage(5.0, channel=1)
        psu.set_current_limit(1.0, channel=1)
        psu.output_enable(True, channel=1)

        voltage = psu.get_voltage(channel=1)
        print(f"V: {voltage.latest:.3f} V")
    ```
  </Tab>
</Tabs>