Skip to content

InputPulseWidth.md

Latest commit

 

History

History
78 lines (53 loc) · 2.32 KB

InputPulseWidth.md

File metadata and controls

78 lines (53 loc) · 2.32 KB
Raw

Overview

This page describes the configuration of RC servo pulse width input interface.

Hardware

The pulse signal is fed to PPM pin that is 5v-tolerant.

        +-----------------< +5v
        |   +-------------< pulse
        |   |       +-----< GND
        |   |       |
+-------|---|---|---|--------------------------+
|      +5v PPM DIR GND                         |

Configuration

First you need to enable the appropriate mode of the PPM interface.

# reg hal.PPM_mode 1

Now you can see how the controller receives the control signal. If variable hal.PPM_signal_caught is 1 then pulse is captured. Use HAL commands to view pulse parameters.

# hal_PPM_get_PERIOD
# hal_PPM_get_PULSE

Select the pulse width range in which you want to work. Put this range to a PPM configuration. We use three point conversion from pulse width to the control value.

# reg ap.ppm_pulse_range[0] <us>
# reg ap.ppm_pulse_range[1] <us>
# reg ap.ppm_pulse_range[2] <us>

Choose what parameter you want to control. You can choose any of the registers available for writing. By default the speed control is selected as a percentage of maximal no load speed. There is a variable pm.s_setpoint_pc.

# reg ap.ppm_reg_ID <reg>

Select the control variable range. So the input pulse width range will be converted to this control range.

# reg ap.ppm_control_range[0] <x>
# reg ap.ppm_control_range[1] <x>
# reg ap.ppm_control_range[2] <x>

Also select the startup range which means an area in which the motor can start. This is necessary to avoid an unexpected start. So to start the motor you will need to apply a control that motor is not dangerous (low speed) and only then increase control signal.

# reg ap.ppm_startup_range[0] <x>
# reg ap.ppm_startup_range[1] <x>

When you change the configuration we recommend to disconnect pulse signal for safety.

Precision

You can change the resolution of the timer that is used to measure the pulse width. By increasing the resolution you increase a minimum pulse rate that can be captured.

# reg hal.PPM_timebase <hz>

The minimum frequency is determined from the expression. Default timebase allows you to capture pulses from 31 Hz.

        timebase
Fmin = ----------
         65536

Maximal timebase allowed is 84000000 Hz that gives a resolution about 12 ns with 1282 Hz minimal pulse frequency.