"Keypecker" is a device for measuring key/button switch response speed and reliability. It uses a stepper motor to (repeatedly) move an actuator rod up and down, and records the time from the start of the movement to a signal edge on one or more digital inputs (channels), for each such movement (pass).
Keypecker can be used to characterize both physical switches and response of devices controlled by switches, provided they report events as digital signal edges.
The device firmware is based on the Zephyr RTOS.
Keypecker is controlled via a TTL-level USART using an interactive shell with an assortment of supported commands (including stock Zephyr commands):
acquire :Acquire a timing measurement on all enabled channels for specified
number of passes (default 1)
adjust :Adjust the "current" (default), "top", or "bottom" actuator
positions interactively
check :Check reliability of all-channel triggering between the top and
bottom positions, over the specified number of passes (default is
one)
clear :Clear screen.
device :Device commands
devmem :Read/write physical memory
Usage:
Read memory at address with optional width:
devmem address [width]
Write memory at address with mandatory width and value:
devmem address <width> <value>
down :Move actuator down (n steps)
get :Get parameters
help :Prints the help message.
history :Command history.
kernel :Kernel commands
measure :Acquire a timing measurement on all enabled channels for specified
number of passes (default 1), and output "brief" (default), or
"verbose" results
off :Turn off actuator
on :Turn on actuator
print :Print the last timing measurement in a "brief" (default) or
"verbose" format
resize :Console gets terminal screen size or assumes default in case the
readout fails. It must be executed after each terminal width
change to ensure correct text display.
set :Set parameters
setup :Make sure the actuator is on, and setup top and bottom positions
specified number of steps (default 1) around the trigger point.
Verify trigger with specified number of passes (default 2).
shell :Useful, not Unix-like shell commands.
swing :Move actuator back-n-forth within n steps around current position,
until interrupted
tighten :Move the top and bottom positions within the specified number of
steps (default 1) around the trigger point. Verify trigger with
specified number of passes (default 2).
up :Move actuator up (n steps)
Here's an example session beginning at the power-on, configuring two channels to detect pressure and release of a directly-connected key switch (Cherry MX Brown), setting up the top and bottom positions tightly around the trigger point, verifying that the trigger is reliable through 32 passes, and then measuring timing of 256 passes (half down, and half up):
*** Booting Zephyr OS build zephyr-v3.3.0-474-geead89e7f22d ***
keypecker:~$ resize
keypecker:~$ set ch 0 down rising DOWN
keypecker:~$ set ch 1 up falling UP
keypecker:~$ setup
Actuator is off.
Move the actuator manually to a point above the trigger, and press Enter.
Press Ctrl-C to abort.
Actuator is on.
The current position is the top.
Moving one step down.
Press up and down arrow keys to move the actuator to a point below the
trigger, and press Enter.
Press Ctrl-C to abort.
Bottom position is set.
Tightening around the trigger point.
Press Ctrl-C to abort.
Setup complete.
keypecker:~$ check 32
100%
keypecker:~$ measure 256
#0 #1
DOWN UP
-------- --------------- ---------------
Both Value Value
-------- --------------- ---------------
Trigs, % +100 +100
Min, us +2680 +1900
Mean, us +2800 +1930
Max, us +2920 +1960
-------- --------------- ---------------
Time Triggers Triggers
-------- --------------- ---------------
Both, us 0 105 0 128
| : |_____________:
1900 | : |_____________|
1963 | : | :
2026 | : | :
2089 | : | :
2152 | : | :
2215 | : | :
2278 | : | :
2341 | : | :
2404 | : | :
2467 | : | :
2530 | : | :
2593 |_ : | :
2656 | |___________: | :
2719 |_____________| | :
2782 | : | :
2845 | : | :
2908 | : | :
-------- --------------- ---------------
keypecker:~$
The plus + signs before the measured numbers indicate overcapture
(bouncing), which is normal for physical switches.
Here's another session. This time a USB keyboard is tested. It signals the detection of a key pressure/release on the rising edge, and the report of that event over USB, on the falling edge, using a single wire. That is connected to two channels - one detecting rising, another - falling edges. After the setup of the trigger point, and a check of 16 triggers, a measurement of 256 passes is taken:
*** Booting Zephyr OS build zephyr-v3.3.0-474-geead89e7f22d ***
keypecker:~$ resize
keypecker:~$ set ch 0 both rising DETECT
keypecker:~$ set ch 1 both falling REPORT
keypecker:~$ setup
Actuator is off.
Move the actuator manually to a point above the trigger, and press Enter.
Press Ctrl-C to abort.
Actuator is on.
The current position is the top.
Moving one step down.
Press up and down arrow keys to move the actuator to a point below the trigger, and press Enter.
Press Ctrl-C to abort.
Bottom position is set.
Tightening around the trigger point.
Press Ctrl-C to abort.
Setup complete.
keypecker:~$ check 16
100%
keypecker:~$ measure 256
#0 #1
DETECT REPORT
-------- --------------- ---------------
Both Value Value
-------- --------------- ---------------
Trigs, % 100 100
Min, us 6080 12500
Mean, us 14320 20500
Max, us 22560 28500
-------- --------------- ---------------
Time Triggers Triggers
-------- --------------- ---------------
Both, us 0 49 0 204
|___________ : | :
6080 | | : | :
7481 | | : | :
8882 | | : | :
10283 | |_: |_____________:
11684 | _____| |_____________|
13085 |_______| : | :
14486 | : | :
15887 | : | :
17288 | : | :
18689 | : |__ :
20090 | : |__| :
21491 | : | :
22892 | : | :
24293 | : | :
25694 | : | :
27095 | : | :
28496 | : | :
-------- --------------- ---------------
keypecker:~$
The data shows that the events are only reported via USB at the interrupt endpoint polling intervals (set to 9ms).
After (or during) capture the results can be output in verbose mode (somewhat truncated for brevity):
keypecker:~$ print verbose
#0 #1
DETECT REPORT
Up/Down Time, us Time, us
-------- --------------- ---------------
Down 14000 21240
Up 6840 12540
Down 8380 12540
Up 9920 12540
Down 11440 12540
Up 12980 20520
(truncated)
Down 9620 12960
Up 11160 12960
Down 12700 12960
Up 14220 20960
-------- --------------- ---------------
Up Value Value
-------- --------------- ---------------
Trigs, % 100 100
Min, us 6240 12500
Mean, us 14400 20500
Max, us 22560 28500
-------- --------------- ---------------
Down Value Value
-------- --------------- ---------------
Trigs, % 100 100
Min, us 6080 12500
Mean, us 10040 16870
Max, us 14000 21240
-------- --------------- ---------------
Both Value Value
-------- --------------- ---------------
Trigs, % 100 100
Min, us 6080 12500
Mean, us 14320 20500
Max, us 22560 28500
-------- --------------- ---------------
Time Triggers Triggers
-------- --------------- ---------------
Up, us 0 29 0 102
|__________ : | :
6080 | | : | :
7481 | _| : | :
8882 | | : | :
10283 | |____: |_____________:
11684 | ________| |_____________|
13085 |____| : | :
14486 | : | :
15887 | : | :
17288 | : | :
18689 | : |__ :
20090 | : |__| :
21491 | : | :
22892 | : | :
24293 | : | :
25694 | : | :
27095 | : | :
28496 | : | :
-------- --------------- ---------------
Down, us 0 25 0 102
|___________ : | :
6080 | | : | :
7481 | |__: | :
8882 | | | :
10283 | _|: |_____________:
11684 | _| : |_____________|
13085 |________| : | :
14486 | : | :
15887 | : | :
17288 | : | :
18689 | : |__ :
20090 | : |__| :
21491 | : | :
22892 | : | :
24293 | : | :
25694 | : | :
27095 | : | :
28496 | : | :
-------- --------------- ---------------
Both, us 0 49 0 204
|___________ : | :
6080 | | : | :
7481 | | : | :
8882 | | : | :
10283 | |_: |_____________:
11684 | _____| |_____________|
13085 |_______| : | :
14486 | : | :
15887 | : | :
17288 | : | :
18689 | : |__ :
20090 | : |__| :
21491 | : | :
22892 | : | :
24293 | : | :
25694 | : | :
27095 | : | :
28496 | : | :
-------- --------------- ---------------
keypecker:~$