2016-01-31 21:48:59 +01:00
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# sigma delta Module
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This module provides access to the sigma-delta component. It's a hardware signal generator that can be routed to any of the GPIOs except pin 0.
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The signal generation is controlled by the [`setprescale()`](#sigma_deltasetprescale) and [`settarget()`](#sigma_deltasettarget) functions.
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2016-02-21 22:32:34 +01:00
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2016-02-21 22:28:01 +01:00
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- 0 < target <= 128<br />
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2016-01-31 21:48:59 +01:00
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t<sub>high</sub> = (prescale + 1) / 80 µs<br />
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t<sub>period</sub> = t<sub>high</sub> * 256 / target
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2016-02-21 22:28:01 +01:00
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- 128 < target < 256<br />
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2016-01-31 21:48:59 +01:00
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t<sub>low</sub> = (prescale + 1) / 80 µs<br />
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t<sub>period</sub> = t<sub>low</sub> * 256 / (256 - target)
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2016-02-21 22:28:01 +01:00
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- target = 0<br />
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2016-01-31 21:48:59 +01:00
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signal stopped at low
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Fixed frequency PWM at ~312.5 kHz is availble with the [`setpwmduty()`](#sigma_deltasetpwmduty) function.
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## sigma_delta.close()
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Stops signal generation and reenables GPIO functionality at the specified pin.
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#### Syntax
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`sigma_delta.close(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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`nil`
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## sigma_delta.setprescale()
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Sets the prescale value.
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#### Syntax
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`sigma_delta.setprescale(value)
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#### Parameters
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`value` prescale 1 to 255
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#### Returns
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`nil`
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#### See also
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[`sigma_delta.settarget()`](#sigma_deltasettarget)
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## sigma_delta.setpwmduty()
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Operate the sigma-delta module in PWM-like mode with fixed base frequency.
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#### Syntax
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`sigma_delta.setpwmduty(ratio)`
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#### Parameters
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`ratio` 0...255 for duty cycle 0...100%, 0 stops the signal at low
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#### Returns
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`nil`
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#### Example
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```lua
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-- attach generator to pin 2
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sigma_delta.setup(2)
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-- set 50% duty cycle ratio (and implicitly start signal)
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sigma_delta.setpwmduty(128)
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-- stop
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sigma_delta.setpwmduty(0)
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-- resume with ~99.6% ratio
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sigma_delta.setpwmduty(255)
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-- stop and detach generator from pin 2
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sigma_delta.close(2)
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```
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## sigma_delta.settarget()
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Sets the target value.
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#### Syntax
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`sigma_delta.settarget(value)
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#### Parameters
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`value` target 0 to 255
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#### Returns
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`nil`
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#### See also
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[`sigma_delta.setprescale()`](#sigma_deltasetprescale)
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## sigma_delta.setup()
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Stops the signal generator and routes it to the specified pin.
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#### Syntax
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`sigma_delta.setup(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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`nil`
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