# Control hardware from a schematic

> Take control, command valves and buttons, and release control from a schematic.

An operator commands hardware by clicking symbols on a [schematic](https://docs.synnaxlabs.com/reference/visualize/schematics). The schematic writes to the command channel of each symbol, and a write task sends the command to the device. Schematics are the only place in the Console where you control hardware by hand.

Before you start:

* Add actuator symbols, such as valves and buttons, to a schematic. In the [control tab](https://docs.synnaxlabs.com/reference/visualize/schematics#control-tab) of each symbol, set its command channel and its state channel.
* Make sure that a [write task](https://docs.synnaxlabs.com/reference/hardware/tasks#write-tasks) listens on each command channel.

You cannot control a snapshot of a schematic.

Enterprise

Your role decides what you can do:

* **Owner** and **Engineer** can take control and [set the schematic authority](https://docs.synnaxlabs.com/reference/control/manual#set-the-schematic-authority).
* **Operator** can take control, but cannot edit schematics. For an Operator, editing is always off, so the first click on a symbol takes control. The schematic always writes at authority 1, and the **Control** tab does not show.
* **Viewer** cannot control hardware, and the control button does not show.

See [users and roles](https://docs.synnaxlabs.com/reference/enterprise/users#roles).

## Take control and command a valve

1. Move the pointer over the schematic, then click the control button () in the top-right corner. Its tooltip is **Acquire control**.

   Editing turns off, and the schematic takes control of the command channel of each symbol. The [control chip](https://docs.synnaxlabs.com/reference/control/manual#control-chips) next to each symbol turns blue.

2. Click a valve. The schematic writes to the command channel of the valve. When the state channel reports the new value, the valve shows as open.

3. When you are done, click the control button again. Its tooltip is **Release control**. The writer with the next highest authority gets control of each channel.

[](https://synnax.nyc3.cdn.digitaloceanspaces.com/docs/console/schematics/valve-dark.mp4#t=0.001)

When editing is off and the schematic does not have control, a click on a symbol takes control first, then sends the command. You can also right-click the schematic and select **Take control** or **Release control**. Closing the schematic also releases control. To release control and edit at the same time, click **Release control and enable editing** in the component toolbar.

If the chip next to a symbol is a red square, a different writer controls the channel, and Synnax drops your commands. See [control authority](https://docs.synnaxlabs.com/reference/control/authority).

## Take absolute control of one channel

1. Click the control chip next to the symbol. The schematic writes to that channel at authority 255, and the chip turns green.
2. To give the channel back, click the green chip. The schematic goes back to its own authority on that channel.

A chip click takes control at 255 even when the chip is blue. A different writer that opened on the channel first at 255 keeps control.

[](https://synnax.nyc3.cdn.digitaloceanspaces.com/docs/control/manual/absolute-control-dark.mp4#t=0.001)

## Set the schematic authority

Each schematic writes at one authority, from 0 to 255. The default is 1, so almost every other writer can take control from it.

1. Turn on editing for the schematic.
2. In the component toolbar, select the **Control** tab.
3. Set **Control authority**.
4. Take control again.

Each Console keeps its own authority for each schematic. The value is not saved with the schematic, so another Console that opens the same schematic writes at 1.

## Set a value and read back the device state

A **Setpoint**, **Text input**, or **Select** symbol writes a value when you click **Set**.

1. Type a number or text, or select an option. The **Set** button turns blue to show an edit that you did not send.
2. Click **Set**. The schematic writes the value to the command channel. The button stays blue until the command channel reports the new value.

If the symbol has a color, the button uses that color, not blue. The field shows the last value on the command channel, from you or from a different writer. If a write fails, the field keeps your value and **Set** stays blue.

To see the value that the device reports, set a [state channel](https://docs.synnaxlabs.com/reference/visualize/schematics#show-the-device-state-on-a-setpoint) on the symbol. The reported value shows under the field. A select shows the name of the option that matches the value. When no new sample arrives within the staleness **Timeout** of the symbol, the reported value shows in the staleness **Color**.

## What each symbol writes

| Symbol                         | Writes                                                       | When                   |
| ------------------------------ | ------------------------------------------------------------ | ---------------------- |
| Valve, pump, and other toggles | `1` when the symbol shows inactive, `0` when it shows active | On click               |
| Button, Fire mode              | `1`                                                          | On release             |
| Button, Momentary mode         | `1` on press, then `0` on release                            | On press and release   |
| Button, Pulse mode             | `1`, then `0` at once                                        | On press               |
| Setpoint                       | The number you type                                          | When you click **Set** |
| Select                         | The number mapped to the option you choose, not its label    | When you click **Set** |
| Text input                     | The text you type                                            | When you click **Set** |

A toggle shows as active when its state channel has a value from 0.9 to 1.1. A toggle with no state channel always shows inactive, so each click writes `1`.

If the **Delay** field of a symbol is set, you must press and hold the symbol for that number of milliseconds before it writes. **Momentary** buttons have no delay. Set the fields in the [control tab](https://docs.synnaxlabs.com/reference/visualize/schematics#control-tab).

## Control chips

The chip next to an actuator symbol shows which writer controls its channel. Move the pointer over the chip to see its tooltip.

| Chip         | Tooltip                                                      | Click does                            |
| ------------ | ------------------------------------------------------------ | ------------------------------------- |
| Gray circle  | Uncontrolled. Click to take control.                         | Takes absolute control (255).         |
| Faded circle | No channel connected                                         | Nothing.                              |
| Blue         | You’re in control. Release the schematic to give up control. | Takes absolute control (255).         |
| Green        | You have absolute control. Click to release.                 | Goes back to the schematic authority. |
| Red          | Not controlled by you. Click to take absolute control.       | Takes absolute control (255).         |

To hide the chip and the colored bar of a symbol, turn off the **Control chip** switch in the control tab of the symbol.

## Control legend

A colored bar next to each actuator symbol shows the color of the writer that controls its channel. The control legend lists each writer that controls a channel on the schematic, with its color:

* **A schematic** shows as the username, with a user icon, and the schematic name.
* **An Arc automation** shows as its Arc name when it runs on the Core, and as its task name when it runs on a Driver.

To change the color of a writer, click its swatch. To move the legend, drag it. To show or hide the legend, use the **Show control state legend** switch in the **Control** tab of the component toolbar.