Breakout Board Analog IO

The following excerpt from the Breakout Board example workflow demonstrates analog IO functionality by computing a ~1Hz sawtooth pattern, outputting it to the analog IO port, and reading it back from the analog IO port. It also saves analog input data.

Analog outputs

The RampGenerator operator generates a sequence of single precision floating point values which comprises ~1Hz sawtooth waveform from -10 to 10. The AnalogOutput updates the analog output port upon receiving a value in the upstream sequence. In the Breakout Board example workflow:

• The AnalogOutput's DeviceName property is set to "BreakoutBoard/AnalogIO". This links the AnalogOutput operator to the corresponding configuration operator.
• The AnalogOutput's DataType property is set to "Volts". The RampGenerator operator computes a sawtooth pattern that consists floats in units of volts, so AnalogOutput must be set to "Volts" to accept this input. Of course, the RampGenerator could be used to produce a sequence of signed 16-bit DAC codes. In that case, DataType property would be set to "S16".

Although a voltage ramp is sent to all the channels, only channel 0 was selected to be a output, so this is the only channel that will be affected. If other channels are configured as output (see Breakout Board Configuration), they will also ramp their voltage. The RampGenerator is a GroupWorkflow that contains multiple Bonsai operators. Examine RampGenerator's internals by pressing Ctrl + Enter when the node is selected:

Tip

To understand how the RampGenerator works, double click each nodes in the workflow while its running to visualize how data is transformed as it flows through each operator. Additionally, the F1 key can be pressed while a node is selected ot bring up its documentation.

This video shows how Bonsai how to examine the data flowing through different elements of workflow as it operates. The "AnalogOutput" window shows the values that are being used by the AnalogOutput operator to update the analog IO port. 12 signals are produced, one for each channel. However, only analog channel 0 is actually updated because it's the only channel configured as output by the BreakoutBoard operator. The "AnalogData" window shows the voltages at the various pins of the analog IO port. They are being read by the the ADCs on the breakout board and produced in Bonsai by the AnalogInput operator. This confirms that only analog channel 0 is outputting the sawtooth waveform.

Analog inputs

Analog input data is recorded from all analog IO channels, regardless of each channels' AnalogIO setting. Because analog inputs and outputs share pins on the breakout board, this enables a loopback of signals from the analog output through the analog input so that a copy of the output signal being sent to external hardware can be saved automatically. The example workflow does exactly this on analog IO channel 0.

The AnalogInput operator receives a sequence of AnalogInputDataFrames with the following properties settings:

• BufferSize is set to 50. Therefore, each frame will contain a 50-element Clock vector and a 12-channel x 50-sample AnalogData matrix. The analog inputs are sampled at 100 kHz per channel so this corresponds to 500 µs of data. That's lower than the minimal latency introduced by the BlockReadSize setting. Therefore, the chosen value for BufferSize will not impose a significant effect on processing latency. The buffer will be filled essentially every time hardware is accessed and propagated instantly.
• DataType is set to Volts. This means that samples will be represented as units of units of voltage in a single-precision floating point type.
• DeviceName is set to "BreakoutBoard/AnalogIO". This links the AnalogInput operator to the corresponding configuration operator.

The MemberSelector operators each select a member from the AnalogInputDataFrame, Clock and AnalogData which contain the AcquisitionClockHz-based sample times and sample values, respectively. The MatrixWriter operators saves the selected members to files with the following format: analog-clock_<filecount>.raw and analog-data_<filecount>.raw, respectively.

Tip

The easiest way to add a MemberSelector to the output of an operator is to right-click the node and hover over Output in the resulting context menu to examine the output type. A MemberSelector can be added by left-clicking the desired expanded property of the Output type.