Merge pull request #134 from open-ephys/issue-94

Motivate heartbeat functionality in breakout

Author: jonnew

articles/hardware/breakout/heartbeat.md

@@ -5,20 +5,22 @@ hardware: true
 device: heartbeat
 ---
 
-The following excerpt from the Breakout Board [example workflow](xref:breakout_workflow)
-demonstrates heartbeat functionality.
+ONIX has a single special device, called a heartbeat, that produces data at regular intervals and is always enabled.
+When data is read from the hardware by software, the reading thread will block until enough data has been produced by
+the hardware. If no devices are enabled, the software would block forever. The heartbeat prevents this from happening
+since it is always enabled and always producing data. In practice, you can ignore the heartbeat functionality. In any
+case, the following excerpt from the Breakout Board [example workflow](xref:breakout_workflow) demonstrates how to
+observe the heartbeat.
 
 ::: workflow
 ![/workflows/hardware/breakout/heartbeat.bonsai workflow](../../../workflows/hardware/breakout/heartbeat.bonsai)
 :::
 
 The <xref:OpenEphys.Onix1.HeartbeatData> operator generates a sequence of
-<xref:OpenEphys.Onix1.HeartbeatDataFrame>s. `HeartbeatData` emits `HeartbeatDataFrame`s at a regular
-interval defined during <xref:breakout_configuration> using the
-<xref:OpenEphys.Onix1.ConfigureBreakoutBoard>'s `Heartbeat BeatsPerSecond` property (in our case 10
-Hz). In the Breakout Board example workflow, the `HeartbeatData`'s `DeviceName` property is set to
-"BreakoutBoard/Heartbeat". This links the `HeartbeatData` operator to the corresponding
-configuration operator. The
-[MemberSelector](https://bonsai-rx.org/docs/api/Bonsai.Expressions.MemberSelectorBuilder.html)
-operator selects the `Clock` member from the `HeartbeatDataFrame` so the user can visualize `Clock`
-data from the `HeartbeatDataFrame`.
+[HeartbeatDataFrames](xref:OpenEphys.Onix1.HeartbeatDataFrame). `HeartbeatData` emits `HeartbeatDataFrames` at a regular
+interval defined during <xref:breakout_configuration> using the <xref:OpenEphys.Onix1.ConfigureBreakoutBoard>'s
+`Heartbeat BeatsPerSecond` property (in our case 10 Hz). The `HeartbeatData`'s `DeviceName` property is set to
+"BreakoutBoard/Heartbeat". This links the `HeartbeatData` operator to the corresponding configuration operator. The
+[MemberSelector](https://bonsai-rx.org/docs/api/Bonsai.Expressions.MemberSelectorBuilder.html) operator selects the
+`Clock` member from the `HeartbeatDataFrame` so the user can visualize the number of clock cycles that have passed for
+a given heartbeat pulse if they double-click the `Clock` node.