Keyboard Control

Learning objectives

To stop a moving device, define its behavior when a key is released or communication is lost, as well as when a key is pressed.

Execution conditions

Reproduce behavior using an input event list. Connecting a real keyboard or device is a separate step that connects the same processing function to the event receiver.

From key input to velocity commands

Starting conditions

$t=\begin{bmatrix}0&0.1&0.2&0.3&0.4&0.5\end{bmatrix}$ s, key=[w,w,release,d,quit,w]. Set w=(1,0) and d=(0,-1) m/s.

Procedure

1. Create a pure function that converts each input into vx, vy, and termination state.
2. Set velocity to 0 on release, and ignore all inputs after quit.
3. Record the command vector and state for each input row.

Results to retain

• A processing table with 6 input rows and a processing function.

events=list(zip([0,.1,.2,.3,.4,.5],['w','w','release','d','quit','w']))
key_velocity={'w':(1.,0.),'s':(-1.,0.),'a':(0.,1.),'d':(0.,-1.)}
# TODO: Write decode(key, stopped), including the stopped state.

Record results and self-check

t [s]:

key:

vx [m/s]:

vy [m/s]:

Termination state:

Points to check

• Does w after quit leave velocity disabled?
• Do undefined keys trigger a stop or an explicitly defined ignore rule?

Time intervals and cumulative movement

Starting conditions

Assume the velocity from activity 1 is maintained until the next input. The initial position is (0,0) m.

Procedure

1. Calculate Δposition=v*Δt for each interval.
2. Create a position table over time and an xy trajectory plot.
3. Compare with the result when all input intervals are changed to .2 s.

Results to retain

• Compare trajectories and final positions under the two interval conditions.

import numpy as np
import matplotlib.pyplot as plt
position=np.zeros(2)
# TODO: Integrate the commands from the first activity over the time intervals.

Record results and self-check

Interval:

Δt [s]:

Velocity [m/s]:

Cumulative position [m]:

Points to check

• Did you distinguish velocity from travel distance?
• Does position remain fixed after termination?

Repeated input and long gaps

Starting conditions

Add a record with repeated w key events at $t\in\{0,.01,.02\}$ s, followed by .5 s without input. Set the timeout to .2 s.

Procedure

1. Compare the behavior to ensure repeated inputs set velocity rather than accumulate acceleration commands.
2. Add a rule to stop when .2 s has elapsed since the last input.
3. Record how commands and positions differ before and after applying a timeout.

Results to retain

• Plots before and after applying a timeout, and 3 sentences describing the behavior rules.

events=[(0.,'w'),(.01,'w'),(.02,'w')]
timeout=.2
# TODO: Calculate commands up to .5 s using a virtual clock with .01 s steps.

Record results and self-check

Time point:

Last input / elapsed time [s]:

Timeout?:

Velocity:

Position:

Points to check

• Can you reproduce behavior using recorded events without sending actual OS keyboard input?
• Are input processing, time updates, and device transmission separated?