good-gui.de

Price Calculation

2021-12-11T05:59:02+00:00

Price Calculator

Do you have used items, that you want to sell but don't know what price tag to put on? Here, you can calculate a suggested price. The item should still be functional. The calculated price here is a suggested price. There is no guaranty, that it is the best price.

Original price:

Age in years:

Category:

Furniture
Major appliance
Consumer electronic
Custom

The equation we use here to calculate the price is: $$ p = n (1 - log_2(\frac{a}{d} + 1)) $$ with new price n, age in years a, and loss in value parameter d. The loss in value parameter is here the time in years it takes a new item to reach a price 0. This should depend on the category of item you want to sell. A chair will not lose value as fast as a cell phone. It also depends on build quality and if the item was well maintained. The values that are used here are rough averages. For a specific case, d can be set in the "Custom" category.

Baha-í Calendar

2021-08-15T05:59:02+00:00

An easy way to add Baha’í dates (Badi Calendar) into a Flutter app is with the open source dart library Badi date.

To install add the following to the “dependencies” section of pubspec.yaml file:

dependencies:
  badi_date: ^1.0.1

and run flutter pub get or dart pub get.

The following shows the library in use:

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import 'package:badi_date/badi_date.dart';

final date1 = BadiDate(day: 1, month: 1, year: 178);
final date2 = BadiDate.fromDate(DateTime.now());

final DateTime start = date1.startDateTime;
final DateTime end = date1.endDateTime;
final BahaiHolyDayEnum? holyDay = date1.holyDay;
final bool = date2.isPeriodOfFast;
final bool = date2.isAyyamIHa;
final BadiDate nextHolyDay = date2.nextHolyDate;

In 3 a BadiDate object is created with Badi day, month, and year. In 4 creation with a Dart DateTime is demonstrated. If the optional parameter longitude and latitude are set, the library will consider the exact sunset time. If not set, 6pm will be assumed for sunset. 6pm will also be used for the polar regions. 6 and 7 return the begin and the end of the Badi date. If the date is a holyday, 8 will return a non null result.

The library is used in the open source Baha’i Calendar app.

dart-suncalc

2021-08-14T05:59:02+00:00

The open source library dart_suncalc calculates the sun position and can offer sun set and sun rise times for different locations and dates. It is a port of the JavaScript library suncalc into Dart and comes with Dart’s sound null-safety. In addition to sun position it can calculate also the position of the moon.

The easiest way to install is to add the following to the “dependencies” section of pubspec.yaml file:

dependencies:
  dart_suncalc: ^0.2.1

and run flutter pub get or dart pub get.

To use the library you can import it with

import 'package:dart_suncalc/dart_suncalc.dart';

Than you calculate sun light times with the following:

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// get today's sunlight times for London
final times = SunCalc.getTimes(date, lat: 51.5, lng: -0.1);

final sunrise = times.sunrise?.toLocal();

Beside the sunrise time, out of the box you will get the sunset, dawn, dusk, nautical dawn, nautical dusk, night, goldenHour, noon, and nadir times. For other times, there is an interface to add additional times:

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// set time for sun angle 45 degree
SunCalc.addTime(45.0, '45-rise', '45-set'});
// get sunlight times for London
final times = SunCalc.getTimes(date, lat: 51.5, lng: -0.1);
// get 45.0 degree time in the first half of the day
final custom = times.custom['45-rise'];

The position of the sun can be calculated with:

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// get position of the sun (azimuth and altitude) at today's sunrise
final sunrisePos = SunCalc.getPosition(times.sunrise, lat: 51.5, lng: -0.1);

// get sunrise azimuth in degrees
final sunriseAzimuth = sunrisePos.azimuth * 180 / PI;

Password

2021-05-18T05:59:02+00:00

Authentication is increasingly becoming important in the internet and as long alternatives are not wide spread, secure passwords are very important. There are several measures to ensure your password is secure like not to use the same password for different services, use a random string, and most important don’t use a password that a random dude on the internet is recommending. Let’s put all these measures aside. The other day, I learned that some people use URLs as password. It is not recommended to do that, but we don’t want to listen to that for a moment, remember that?

If you are looking for a URL that you can use as a password, you could consider my homepage www.i1u.de. It’s brief and you can remember it easily and look if you capitalize some letter, www.I1U.de has everything most password validators require: upper and lower case letters, number, special characters, and it has 10 characters. Perfect. I’m not saying you should use it as your password. I’m just saying if you do, I don’t mind.

A Moment Please

2018-11-15T16:39:02+00:00

Have you ever been in that situation? Someone asks you: "What time is it?". You start to answer: "It's 11, and 23 minutes", "...and 45 seconds, haha" you are made fun of for beeing precise.

One of my favorit watch faces on my smart watch is the fuzzy clock, where the approximate time is given.

source code

From software developer side, it is anoying to have year, month, day, hour, minute, and second all to describe, one thing, time. Thank God, we have unix time. Unix time is a single value. A number consisting of 64 ones and zeros (or a decimal integer) to address all seconds from billions of years before the big bang up to billions of years from now.

source code

While it's easy to develop software with unix time, it's impractical for everyday use. Wouldn't it be nice if we could remove some clutter and have less parameter for time. I have given it some thought and tried to come up with something for the time of the day. What if instead hour, minute and second just have a single number. I call it moment. 240 moments are a day, as everyone knowes. So one hour is ten moments. 1 moment is 6 minutes. In my experience, if someone asks me to wait just one moment, only five minutes not more, I usualy end up waiting 6. Hence the name moment. Moments can also be used as fractions. If someone does not need a full moment, she can ask for half a moment.

It turns out, I'm not the first who comes up with an alternative time unit named moment. Not even 240 for a day is something new (citation needed). There have been many ideas and suggestions. I like 240 moments for a day. It has advantages over 100 for a day. The first advantage is: you can easily convert hour and minute to moments. For example, 11:30 is 115 moments = hours x 10 + 30 minutes is 5 moments. The second advantage is 240 can be evenly divided by 3. So, you can for example say an adult should sleep one third of a day or 80 moments. 100 divided by 3 is 33.33333. Not so nice.

Don't confuse my moment time unit with military time. Military time is horrible for a software developer. Military time you can't just add times. 1630 + 30 is not 1660. It's 1700. But in moments 165 + 5 is equal 170. It all works out.

source code

Light Switch

2017-11-01T05:59:02+00:00

Smart bulbs and lights are a dream for hackers. There are light switches available for smart bulbs but why buy if you can DIY. My light switch should have two buttons. One to turn on and to make the lights brighter and one to turn off or darken the lights. If both buttons are pressed the lights should change colors. The new color should be a color from a predefined set of colors. Here, one way to go: You need

Smart lights (of course)
computer with GPIO (e.g. Raspberry Pi)
Two buttons, two LEDs, resistances, cables, optionally a board

Wire the one button to GPIO 35 and one to 37 and one LED to 38 and one to 40.

The following python script does the job for the Philips Hue system

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#!/usr/bin/python3

# Import the required module. 
import RPi.GPIO as GPIO, time
import requests
import json
import time

# Set the mode of numbering the pins. 
GPIO.setmode(GPIO.BOARD)
# GPIO 38 and 40 is the output. 
GPIO.setup(38, GPIO.OUT)
GPIO.setup(40, GPIO.OUT)
# GPIO 35 and 37 is the input. 
GPIO.setup(35, GPIO.IN)
GPIO.setup(37, GPIO.IN)
# Initialise GPIO21 to high (true) so that the LED is off. 
GPIO.output(40, False)
GPIO.output(38, False)

# Base URL 
url = "http://[IP]/api/[TOKEN]/groups/[GROUP ID]"
hue_index = 4

def change_brightnes(change):
    r = requests.get(url)
    brightnes = min(int(r.json()["action"]["bri"] + change), 254)
    if brightnes > 0:
        requests.put(url+"/action", data = json.dumps({"bri": brightnes, "on": True, "transitiontime": 5}))
    else:
        requests.put(url+"/action", data = json.dumps({"bri": 1, "on": False, "transitiontime": 50}))

def change_hue():
    global hue_index
    hues = [0, 5461, 10922, 16384, 21845, 25500, 27306, 32767, 38229, 43690, 46920, 49151, 54612, 60074]
    requests.put(url+"/action", data = json.dumps({"hue": hues[hue_index], "sat": 254}))
    hue_index = (hue_index + 1) % len(hues)


def button_press(channel):  
    global start
    global double
    led = channel + 3
    if GPIO.input(channel) == 1:
        GPIO.output(led, True)
        double = True if GPIO.input(35) == GPIO.input(37) else False
        start = time.time()
    if GPIO.input(channel) == 0:
        elapsed = time.time() - start
        GPIO.output(led, False)
        if double == True and GPIO.input(35) + GPIO.input(37) == 1:
            change_hue()
        elif double == False:
            sign = 1 if channel == 37 else -1
            change = sign * elapsed * 50
            change_brightnes(change)
 
GPIO.add_event_detect(35, GPIO.BOTH, callback=button_press)
GPIO.add_event_detect(37, GPIO.BOTH, callback=button_press)

try:
    while 1:
        time.sleep(1)
finally:
        GPIO.cleanup()

The GPIO pins are set up (lines 9-19) and set up the base URL with the IP address to the Hue bridge and the authentication token as well as the ID of the light group that should be controlled (line 22). You can find out on the Hue developer page how to get a token. A function is defined to change the brightness (line 25). The current brightness is requested (line 26) and the new brightness is set as current plus change but not more than the maximum of 254 (line 27). If the new brightness is greater than 0 the brightness is changed (line 29) otherwise the lights are turned of with a transition time of 5 s (line 31). A function to change colors is defined (line 33) with a set of colors (line 35). The color is set (line 36) and the an index is set that loops through all colors in the set (line 37). And a function for checking the button events is defined (line 40). We assign an LED to the events pin (line 43). If the button event was a press event (line 44) the controll LED is turned on (line 45), we check if both buttons are pressed (line 46), and start the timer (line 47). If the button event was a release event (line 48) the elapsed time since button press is calculated (line 49), the control LED is turned off (line 50), and we check if the other button is pressed (line 51). If so the color is changed (line 52) if not we check if the other button have been pressed while this one was pressed (line 53). Only if it hadn’t a sign is assigned to mark a increase or decrease of brightness (line 54), the change of brightness is calculated depending on how long the button was pressed (line 55), and the brightness is changed (line 56). For each button an event is set for press and release and the just defined function is set as callback (line 58 and 59). A while loop prevents our program to finish by it self (line 62) and we clean up in case of interruption (line 65).

Turn it down

2017-08-16T05:59:02+00:00

When I watch TV at nights, I often don’t pay attention on the volume. To avoid angry neighbours, I wrote a python script to turn the volume down on my smart TV. The most difficult part of this task was to find some kind information on the TV API because there is no public documentation. Here is the script for a Philips TV

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import requests
import json
 
try:
    r = requests.get('http://[TV_IP]:1925/1/audio/volume')
    if r.json()["current"]<10 and not r.json()["muted"]:
        requests.post('http://[TV_IP]:1925/1/audio/volume', 
            data = json.dumps({'current':10}))
except OSError:
    exit

It requests volume information (line 5) and checks if the volume is above 10 and not muted (line 6). If so it will reduce the volume to 10 (line 7). Exceptions need to be caught if the TV is not reachable/ TV is off (line 9). A cron job runs the script every night at 10pm. Create the cron job with crontab -e and add
00 22 * * * [path to script]
A nice side effect is a visual and audible yet inconspicuous notification for when it turns 10 pm.

And the Nobel Goes To…

2013-10-18T05:59:02+00:00

This years Nobel prize in chemistry is awarded to Martin Karplus, Michael Levitt, and Arieh Warshel. Three of my fellow computational scientist who worked in the field of quantum mechanics and molecular mechanics simulation. Congratulations from my side. You really deserve that prize. The other day I was telling one of my students that the time for experimentalist is up. They had a good run but from now on we, the computational guys, are the new heros. There is a new sheriff in town.

Partition Problems

2013-10-16T05:59:02+00:00

We got a new Linux workstation in our lab and guess who had to set it up. I had to change the partitioning of the hard disk and while I was doing that I also updated the software. The software update made a reboot necessary and someone forgot to change the partition table before rebooting. That caused the system not to boot completely. In the file /etc/fstab the partitions where listed with the partition ID instead of the device name. Because the old partitions were deleted the system could not boot them. The system booted / in read only and didn’t allow to change that. So, there was no way to change fstab. It’s not important whose fault it was. We don’t want to point fingers on someone, especially not at me. Here is what I did to save the day.

Stay calm and don’t panic.
Open fstab with:
vi /etc/fstab
The file opens in read only
Note down the partition ID and type of the partition that is missing
Use fdisk to change the partition ID by typing:
fdisk disk [identifier] (e.g. /dev/sdb1)
x
i
[partition ID from step 3]
w
Make sure that the partition type hasn’t change from what you have from step 3. If you have changed the type while you were partitioning the system, change it back.
Reboot

That should solve the problem. No data lost. Once the system boots OK you can change the fstab and than change also the partition ID if needed.

What Computer

2013-09-08T05:59:02+00:00

The other day someone asked me what computer we have. What is an appropriate answer to that question? There is obviously the answer “a grey one!”. In the 80s you could answer a 386 PC, a Mac, an Amiga, and so on. But what do you say now? Nowadays even Macs have Intel inside. So what should I say instead the CPU type? Mac user are usually very specific about what computer they have, all the time. Instead losing the laptop, they cannot find the MacBook Air. That does apply to other Apple products, as well. Apple user never look up something on a tablet but on a iPad, they don’t call someone on there phone, instead they send a text with their iPhone, and I don’t have an awesome song on my MP3 player but awful songs on my 3rd generation 32GB iPod touch. So, how do you answer the question what computer you have? Do you say what operation system is running on it? Do you describe the hardware in detail? Or is it the color?