Bicycling For The Fun of It All

Somewhere out there, you’ll find his video:

Photo Op - 2020-11-09 - 287
Photo Op – 2020-11-09 – 287

Everybody needs a reason to smile!

Bonus: enough vehicles to keep the signal at Burnett green.

In the unlikely event you were wondering, 287 is the frame number from the video-to-still conversion:

ffmpeg -ss 00:03:30 -i /mnt/video/AS30V/2020-11-09/MAH07624.mp4 -t 20 -f image2 -q 1 'Photo Op - 2020-11-09 - '%03d.jpg

All in all, a fine day for a ride …

XFCE vs. Screen Locking

For reasons not relevant here, I was asked to tweak an XFCE 20.04 installation to not ask for a password after the screen power-saver kicks in. There’s no need for a screensaver with an LCD panel, so this should be straightforward, as per the XFCE 18.04 setup:

XFCE Power Manager Light Locker settings 18.04
XFCE Power Manager Light Locker settings 18.04

Which had no effect.

For some reason, perhaps having to do with an upgrade from 18.04 to 20.04, Light Locker wasn’t actually handling the screen locking; some dedicated searching suggested this is a problem of long standing.

So tweak the Lock Screen settings of the screen saver that’s not in use:

XFCE Screensaver Lock Screen Preferences - 20.04
XFCE Screensaver Lock Screen Preferences – 20.04

If you’re doing this remotely, adding a stanza to ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-screensaver.xml should suffice:

<?xml version="1.0" encoding="UTF-8"?>

<channel name="xfce4-screensaver" version="1.0">
  <property name="saver" type="empty">
    <property name="mode" type="int" value="0"/>
  </property>
  <property name="lock" type="empty">
    <property name="enabled" type="bool" value="false"/>
  </property>
</channel>

The threat model for this particular installation is “minimal”.

Raspberry Pi Camera vs. RTSP Streaming

It Would Be Nice to turn the various Raspberry Pi camera boxen around here into more-or-less full-automatic IP streaming cameras, perhaps using RTSP, so as to avoid having to start everything manually, then restart the machinery after a trivial interruption. I naively thought video streaming was a solved problem, especially on an RPi, particularly with an Official RPi Camera, given the number of solutions found by casual searching with the obvious keywords.

As far as I can tell, however, all of the recommended setups fail in glorious / amusing / tragic ways. Some failures may be due to old configurations no longer applicable to new software, but I’m nowhere near expert experienced enough to figure out what’s broken and how to fix anything in particular.

Doing RTSP evidently requires the live555.com Streaming Media libraries & test suite. Compiling requires adding -DNO_SSL=1 to the COMPILE_OPTS line in the Makefile, then letting it bake it for a while.

The v4l2rtspserver code fetches & cleanly compiles its version of the live555 code, then emits various buffer overflow errors while streaming; the partial buffers clearly show how the compression works on small blocks in successive lines. Increasing various buffer sizes from 60 kB to 100 kB to 300 kB had little effect. This may have to do with the stream’s encoding / compression methods / bit rates, none of which seem amenable to random futzing.

Another straightforward configuration compiled fine, but VLC failed to actually show the stream, perhaps due to differences between the old version of Raspbian (“Stretch”) and the new version of Raspberry Pi OS (“Buster”).

Running the RPi camera through the Video4Linux2 interface to create a /dev/video0 device seems to work, but controlling the camera’s exposure (and suchlike) with v4l2_ctl behaves erratically. Obvious effects, like rotation & flipping, work fine, but not the fine details along the lines of auto exposure and color modes.

Attempting to fire raspivid through cvlc to produce an RTSP stream required installing VLC on a headless Raspberry Pi, plus enough co-requisite packages to outfit world+dog+kitchenSink. After all the huffing & puffing wound down, the recommended VLC parameters failed to produce an output stream. The VLC doc regarding streaming is, to me, impenetrable, so I have no idea how to improve the situation; I assume RTSP streaming is possible, just not by me.

Whenever any of those lashups produced any video whatsoever, the images suffered from tens-of-seconds latency, dropped frames, out-of-order video updates, and generally poor behavior. Some maladies certainly came from the aforementioned inappropriate encoding / compression methods / bit rates.

The least horrible alternative seems to be some variation on the original theme of using raspivid to directly create a tcp stream or firing raspivid into netcat to the same effect, then re-encoding it on a beefier PC as needed. I’m sure systemd can automagically restart raspivid (or, surely, a script with all the parameters) after it shuts down.

So far, this has been an … unsatisfactory … experience, but now I can close a dozen browser tabs.

Mini-Lathe Ball Drilling Fixture

Despite successfully drilling holes in a few plastic balls, I wanted a somewhat less terrifying setup than this:

Micromark Ball Vise - lathe ball hack
Micromark Ball Vise – lathe ball hack

The stiffness of the bike helmet mirror mount suggested a similar clamp would have enough griptivity to immobilize the ball while cutting it in the lathe:

Helmet Mirror Mount - 10 mm ball
Helmet Mirror Mount – 10 mm ball

Building the clamp around the lathe’s three-jaw lathe chuck eliminates the need for screws / washers / inserts:

Lathe Ball Fixture - 19 mm - Show
Lathe Ball Fixture – 19 mm – Show

The Ah-ha! moment came when I realized the fixture can expose half of the ball’s diameter for drilling while clamping 87% of its diameter, because 0.5 = sin 30° and 0.87 = cos 30°:

Lathe Ball Fixture - 19 mm - Show - front orthogonal
Lathe Ball Fixture – 19 mm – Show – front orthogonal

That’s an orthogonal view showing 13% of the ball radius sticking out of the fixture; it’s 6% of the diameter.

Which looks like this in real life:

Lathe Ball Fixture - 19 mm - sections with ball
Lathe Ball Fixture – 19 mm – sections with ball

The socket is offset toward the tailstock end of the clamp (on the right in the picture) to expose half its diameter flush with the surface perpendicular to the lathe axis. The other side necks down into a cylinder of the same diameter to clear the drill bit.

This works nicely until the ball diameter equals the chuck jaw’s 20 mm length, whereupon larger balls protrude into the chuck body’s spindle opening. Although I haven’t yet built one, the 25 mm balls in my Box o’ Bearings should fit, with exceedingly sissy cuts required for large holes.

The fixture doesn’t require support material, because the axial holes eliminate the worst of the overhang. Putting the tailstock side flat on the platform gives it the best-looking surface:

Lathe Ball Fixture - 19 mm - Slic3r - equator
Lathe Ball Fixture – 19 mm – Slic3r – equator

The kerf between the segments ensures the jaws can apply pressure to the ball, whereupon the usual crappy serrated 3D printed surface firmly grabs it.

The fixture is a slip fit on the chuck jaws:

Lathe Ball Fixture - 19 mm - installed
Lathe Ball Fixture – 19 mm – installed

Tightening the jaws shoves them all the way into the fixture’s slots and clamps the ball:

Lathe Ball Fixture - 19 mm - center drill
Lathe Ball Fixture – 19 mm – center drill

Overtightening the chuck will (probably) compress the ball around the drill, which will (best case) give you slightly oversize holes or (worst case) cause the ball to seize / melt around the drill bit, so sleaze up to the correct hole diameter maybe half a millimeter at a time:

Lathe Ball Fixture - 19 mm - 6 mm drill
Lathe Ball Fixture – 19 mm – 6 mm drill

That fixture exposes 9.5 mm = 19/2 of the ball. The drill makes a 6 mm hole to fit the telescoping shaft seen above.

Obviously, you must build a custom fixture for every ball diameter in your inventory, which is no big deal when you have a hands-off manufacturing process. Embossing the diameter into the fixture helps match them, although the scribbled Sharpie isn’t particularly elegant.

The OpenSCAD source code as a GitHub Gist:

// Lathe Ball Drilling Fixture
// Ed Nisley KE4ZNU 2020-11
/* [Layout options] */
Layout = "Build"; // [Build, Show, Body, Jaws]
BallDia = 10.0; // [5.0:0.5:25.0]
/* [Extrusion parameters] */
/* [Hidden] */
ThreadThick = 0.25;
ThreadWidth = 0.40;
HoleWindage = 0.2;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
function IntegerLessMultiple(Size,Unit) = Unit * floor(Size / Unit);
Protrusion = 0.1; // make holes end cleanly
inch = 25.4;
ID = 0;
OD = 1;
LENGTH = 2;
//* [Basic dimensions] */
Chuck = [21.0,100.0,20.0]; // chuck bore, OD, jaw length
Jaw = [Chuck[LENGTH],15.0,12.0]; // jaw free length, base width, first step radius
JawInclAngle = 112; // < 120 degrees for clearance!
JawAngle = JawInclAngle/2; // angle from radius
WallThick = 5.0; // min wall thickness
Kerf = 0.75; // space between clamp blocks
ClampSides = 8*(2*3);
ClampBore = BallDia/2; // clear bore through clamp
ClampAngle = asin(ClampBore/BallDia); // angle from lathe axis to clamp front
Plate = [ClampBore,
BallDia + 2*WallThick + 2*Jaw.z,
Jaw.x];
LegendDepth = 1*ThreadWidth;
ShaftOD = 3.6; // sample shaft
ShowGap = 1.5;
//----------------------
// Chuck jaws
// Real jaws have a concave radiused tip we simply ignore
module ChuckJaws(l=Jaw.x,r=10) {
for (a=[0:120:240])
rotate(a)
linear_extrude(height=l)
translate([r,0])
difference() {
translate([Chuck[OD]/4,0])
square([Chuck[OD]/2,Jaw.y],center=true);
for (i=[-1,1])
rotate(i*(90 - JawAngle))
translate([-Jaw.z/2,0])
square([Jaw.z,2*Jaw.y],center=true);
}
}
//----------------------
// Clamp body
module ClampBlocks() {
difference() {
cylinder(d=Plate[OD],h=Plate[LENGTH],$fn=ClampSides); // main disk
translate([0,0,-Protrusion]) // central bore
cylinder(d=ClampBore,h=2*Plate[LENGTH],$fn=ClampSides);
for (a=[0:120:240]) // kerf slits
rotate(60 + a)
translate([Plate[OD]/2,0,Protrusion])
cube([Plate[OD],Kerf,2*Plate[LENGTH]],center=true);
translate([0,0,BallDia/2 * cos(ClampAngle)]) // ball socket
sphere(d=BallDia,$fn=ClampSides);
for (a=[0:120:240]) { // legend
rotate(4.5*360/ClampSides + a)
translate([Plate[OD]/2 - LegendDepth,0,Plate[LENGTH]/2])
rotate([0,90,0])
linear_extrude(height=LegendDepth + Protrusion,convexity=10)
mirror([0,0,0])
text(text=str(BallDia," mm"),size=2.5,spacing=1.20,font="Arial:style:Bold",halign="center",valign="center");
rotate(-4.5*360/ClampSides + a)
translate([Plate[OD]/2 - LegendDepth,0,Plate[LENGTH]/2])
rotate([0,90,0])
linear_extrude(height=LegendDepth + Protrusion,convexity=10)
mirror([0,0,0])
text(text="KE4ZNU",size=2.5,spacing=1.20,font="Arial:style:Bold",halign="center",valign="center");
}
}
}
//----------------------
// Clamp with jaw cutouts
module ClampBody() {
difference() {
ClampBlocks();
translate([0,0,-Protrusion])
ChuckJaws(l=Jaw.x + 2*Protrusion,r=BallDia/2 + WallThick);
}
}
//----------------------
// Lash it together
if (Layout == "Body") {
ClampBlocks();
}
if (Layout == "Jaws") {
ChuckJaws();
}
if (Layout == "Build") {
ClampBody();
}
if (Layout == "Show") {
ClampBody();
color("ivory",0.2)
ChuckJaws(r=BallDia/2 + WallThick + ShowGap); // move out for E-Z viewing
color("red",0.4)
translate([0,0,-Jaw.x/2])
cylinder(d=ShaftOD,h=2*Jaw.x,$fn=ClampSides,center=false);
color("white",0.5)
translate([0,0,BallDia/2 * cos(ClampAngle)]) // ball socket
sphere(d=BallDia,$fn=ClampSides);
}

The dimension doodles, including some notions that didn’t work:

Lathe Ball Clamp - dimension doodles
Lathe Ball Clamp – dimension doodles

Arducam Motorized Focus Camera: Rotary Encoder and Equation

Mashing rotary encoder reading together with the focus-distance-to-DAC equation produces well-behaved camera focusing.

First, set up another test range:

Arducam Motorized Focus Camera - desktop test range
Arducam Motorized Focus Camera – desktop test range

Run the test code:

# Simpleminded focusing test for
#  Arducam Motorized Focus Camera
# Gets events through evdev from rotary encoder knob

# Ed Nisley - KE4ZNU
# 2020-10-20

import sys
import math
import evdev
import smbus

# useful functions

def DAC_from_distance(dist):
    return math.trunc(256*(10.8 + 2180/dist))

# write DAC word to camera I2C bus device
#  and ignore the omnipresent error return

def write_lens_DAC(bus,addr,val):
    done = False
    while not done:
        try:
            bus.write_word_data(addr,val >> 8,val & 0xff)
        except OSError as e:
            if e.errno == 121:
#                print('OS remote error ignored')
                done = True
        except:
            print(sys.exc_info()[0],sys.exc_info()[1])
        else:
            print('Write with no error!')
            done = True

# set up focus distances

closest = 50            # mm
farthest = 500
nominal = 100           # default focus distance

foci = [n for n in range(closest,nominal,5)] \
     + [n for n in range(nominal,250,10)]  \
     + [n for n in range(250,1501,25)]

# compute DAC equivalents for each distance

foci_DAC = list(map(DAC_from_distance,foci))

focus_index = foci.index(nominal)

# set up the I2C bus

f = smbus.SMBus(0)
lens = 0x0c

# set up the encoder device handler
# requires rotary-encoder dtoverlay aimed at pins 20 & 21

d = evdev.InputDevice('/dev/input/by-path/platform-rotary@14-event')
print('Rotary encoder device: {}'.format(d.name))

# set initial focus

write_lens_DAC(f,lens,foci_DAC[focus_index])

# fetch I2C events and update the focus forever

for e in d.read_loop():
#    print('Event: {}'.format(e))

    if e.type == evdev.ecodes.EV_REL:
#        print('Rel: {}'.format(e.value))

        if (e.value > 0 and focus_index < len(foci) - 1) or (e.value < 0 and focus_index > 0):
            focus_index += e.value

        dist = foci[focus_index]
        dac = foci_DAC[focus_index]

        print('Distance: {:4d} mm DAC: {:5d} {:04x} i: {:3d}'.format(dist,dac,dac,focus_index))

        write_lens_DAC(f,lens,dac)

Because the knob produces increments of ±1, the code accumulates them into an index for the foci & foci_DAC lists, then sends the corresponding entry from the latter to the lens on every rotary encoder event.

And then It Just Works!

The camera powers up with the lens focused at infinity (or slightly beyond), but setting it to 100 mm seems more useful:

Arducam Motorized Focus Camera - 100 mm
Arducam Motorized Focus Camera – 100 mm

Turning the knob counterclockwise runs the focus inward to 50 mm:

Arducam Motorized Focus Camera - 50 mm
Arducam Motorized Focus Camera – 50 mm

Turning it clockwise cranks it outward to 1500 mm:

Arducam Motorized Focus Camera - 1500 mm
Arducam Motorized Focus Camera – 1500 mm

The mug is about 300 mm away, so the depth of field extends from there to infinity (and beyond).

It needs more work, but now it has excellent upside potential!

Raspberry Pi Rotary Encoder: Knob Switch Key

The rotary encoder knob I’m using for these tests has a pushbutton switch in its shaft:

RPi rotary encoder - improved test fixture
RPi rotary encoder – improved test fixture

Now that I know where to look, it turns out there’s a Raspberry Pi overlay for that:

Name:   gpio-key
Info:   This is a generic overlay for activating GPIO keypresses using
        the gpio-keys library and this dtoverlay. Multiple keys can be
        set up using multiple calls to the overlay for configuring
        additional buttons or joysticks. You can see available keycodes
        at https://github.com/torvalds/linux/blob/v4.12/include/uapi/
        linux/input-event-codes.h#L64
Load:   dtoverlay=gpio-key,<param>=<val>
Params: gpio                    GPIO pin to trigger on (default 3)
        active_low              When this is 1 (active low), a falling
                                edge generates a key down event and a
                                rising edge generates a key up event.
                                When this is 0 (active high), this is
                                reversed. The default is 1 (active low)
        gpio_pull               Desired pull-up/down state (off, down, up)
                                Default is "up". Note that the default pin
                                (GPIO3) has an external pullup
        label                   Set a label for the key
        keycode                 Set the key code for the button

Snuggle the button configuration next to the encoder in /boot/config.txt:

dtoverlay=rotary-encoder,pin_a=20,pin_b=21,relative_axis=1,steps-per-period=2<br>dtoverlay=gpio-key,gpio=26,keycode=83,label="KNOB"

I haven’t yet discovered where the label text appears, because I picked a keycode defining the button as the decimal point key on a numeric keypad. Perhaps one could create a unique key from whole cloth, but that’s in the nature of fine tuning. In any event, pressing / releasing the button produces key-down / key-up events just like you’d get from a real keyboard.

The four pins required for the encoder + switch make a tidy block at the right (in this view, left as shown above) end of the RPi’s header:

Raspberry Pi pinout
Raspberry Pi pinout

If you needed the SPI1 hardware, you’d pick different pins.

Reboot that sucker and another input device appears:

ll /dev/input/by-path/
total 0
lrwxrwxrwx 1 root root 9 Oct 18 10:00 platform-button@1a-event -> ../event0
lrwxrwxrwx 1 root root 9 Oct 18 10:00 platform-rotary@14-event -> ../event2
lrwxrwxrwx 1 root root 9 Oct 18 10:00 platform-soc:shutdown_button-event -> ../event1

As with the encoder device, the button device name includes the hex equivalent of the pin number: 26 decimal = 0x1a.

Run some code:

# Keypress from Raspberry Pi GPIO pin using evdev
# Add to /boot/config.txt
#  dtoverlay=gpio-key,gpio=26,keycode=83,label="KNOB"

import evdev

b = evdev.InputDevice('/dev/input/by-path/platform-button@1a-event')
print('Button device: {}'.format(b.name))

print(' caps: {}'.format(b.capabilities(verbose=True)))
print(' fd: {}'.format(b.fd))

for e in b.read_loop():
    print('Event: {}'.format(e))
    if e.type == evdev.ecodes.EV_KEY:
        print('Key {}: {}'.format(e.code,e.value))

Which produces this output:

Button device: button@1a
caps: {('EV_SYN', 0): [('SYN_REPORT', 0), ('SYN_CONFIG', 1)], ('EV_KEY', 1): [('KEY_KPDOT', 83)]}
fd: 3
Event: event at 1603036309.683348, code 83, type 01, val 01
Key 83: 1
Event: event at 1603036309.683348, code 00, type 00, val 00
Event: event at 1603036310.003329, code 83, type 01, val 00
Key 83: 0
Event: event at 1603036310.003329, code 00, type 00, val 00

All in all, that was easy …

Raspberry Pi Rotary Encoder: evdev Proof of Concept

After Bill Wittig pointed me in the right direction, writing a Python program to correctly read a rotary encoder knob on a Raspberry Pi is straightforward. At least given some hints revealed by knowing the proper keywords.

First, enhance the knob’s survivability & usability by sticking it on a perfboard scrap:

RPi rotary encoder - improved test fixture
RPi rotary encoder – improved test fixture

Then find the doc in /boot/overlays/README:

Name: rotary-encoder
Info: Overlay for GPIO connected rotary encoder.
Load: dtoverlay=rotary-encoder,
=
Params: pin_a GPIO connected to rotary encoder channel A
(default 4).
pin_b GPIO connected to rotary encoder channel B
(default 17).
relative_axis register a relative axis rather than an
absolute one. Relative axis will only
generate +1/-1 events on the input device,
hence no steps need to be passed.
linux_axis the input subsystem axis to map to this
rotary encoder. Defaults to 0 (ABS_X / REL_X)
rollover Automatic rollover when the rotary value
becomes greater than the specified steps or
smaller than 0. For absolute axis only.
steps-per-period Number of steps (stable states) per period.
The values have the following meaning:
1: Full-period mode (default)
2: Half-period mode
4: Quarter-period mode
steps Number of steps in a full turnaround of the
encoder. Only relevant for absolute axis.
Defaults to 24 which is a typical value for
such devices.
wakeup Boolean, rotary encoder can wake up the
system.
encoding String, the method used to encode steps.
Supported are "gray" (the default and more
common) and "binary".

Add a line to /boot/config.txt to configure the hardware:

dtoverlay=rotary-encoder,pin_a=20,pin_b=21,relative_axis=1,steps-per-period=2

The overlay enables the pullup resistors by default, so the encoder just pulls the pins to common. Swapping the pins reverses the sign of the increments, which may be easier than swapping the connector after you have it all wired up.

The steps-per-period matches the encoder in hand, which has 30 detents per full turn; the default value of 1 step/period resulted in every other detent doing nothing. A relative axis produces increments of +1 and -1, rather than the accumulated value useful for an absolute encoder with hard physical stops.

Reboot that sucker and an event device pops up:

ll /dev/input
total 0
drwxr-xr-x 2 root root 80 Oct 18 07:46 by-path
crw-rw---- 1 root input 13, 64 Oct 18 07:46 event0
crw-rw---- 1 root input 13, 65 Oct 18 07:46 event1
crw-rw---- 1 root input 13, 63 Oct 18 07:46 mice

I’m unable to find the udev rule (or whatever) creating those aliases and, as with all udev trickery, the device’s numeric suffix is not deterministic. The only way you (well, I) can tell which device is the encoder and which is the power-off button is through their aliases:

ll /dev/input/by-path/
total 0
lrwxrwxrwx 1 root root 9 Oct 18 07:46 platform-rotary@14-event -> ../event0
lrwxrwxrwx 1 root root 9 Oct 18 07:46 platform-soc:shutdown_button-event -> ../event1

The X axis of the mice device might report the same values, but calling a rotary encoder a mouse seems fraught with technical debt.

The name uses the hex equivalent of the A channel pin number (20 = 0x14), so swapping the pins in the configuration will change the device name; rewiring the connector may be easier.

Using the alias means you always get the correct device:

# Rotary encoder using evdev
# Add to /boot/config.txt
#  dtoverlay=rotary-encoder,pin_a=20,pin_b=21,relative_axis=1,steps-per-period=2
# Tweak pins and steps to match the encoder

import evdev

d = evdev.InputDevice('/dev/input/by-path/platform-rotary@14-event')
print('Rotary encoder device: {}'.format(d.name))

position = 0

for e in d.read_loop():
    print('Event: {}'.format(e))
    if e.type == evdev.ecodes.EV_REL:
        position += e.value
        print('Position: {}'.format(position))

Which should produce output along these lines:

Rotary encoder device: rotary@14
Event: event at 1603019654.750255, code 00, type 02, val 01
Position: 1
Event: event at 1603019654.750255, code 00, type 00, val 00
Event: event at 1603019654.806492, code 00, type 02, val 01
Position: 2
Event: event at 1603019654.806492, code 00, type 00, val 00
Event: event at 1603019654.949199, code 00, type 02, val 01
Position: 3
Event: event at 1603019654.949199, code 00, type 00, val 00
Event: event at 1603019655.423506, code 00, type 02, val -1
Position: 2
Event: event at 1603019655.423506, code 00, type 00, val 00
Event: event at 1603019655.493140, code 00, type 02, val -1
Position: 1
Event: event at 1603019655.493140, code 00, type 00, val 00
Event: event at 1603019655.624685, code 00, type 02, val -1
Position: 0
Event: event at 1603019655.624685, code 00, type 00, val 00
Event: event at 1603019657.652883, code 00, type 02, val -1
Position: -1
Event: event at 1603019657.652883, code 00, type 00, val 00
Event: event at 1603019657.718956, code 00, type 02, val -1
Position: -2
Event: event at 1603019657.718956, code 00, type 00, val 00
Event: event at 1603019657.880569, code 00, type 02, val -1
Position: -3
Event: event at 1603019657.880569, code 00, type 00, val 00

The type 00 events are synchronization points, which might be more useful with more complex devices.

Because the events happen outside the kernel scheduler’s notice, you (well, I) can now spin the knob as fast as possible and the machinery will generate one increment per transition, so the accumulated position changes smoothly.

Much better!