Cron configuration improvements for Raspberry Pi

One of the shortcomings or RPi for (m)any serious applications is that it lacks a hardware clock so when it starts, the clock is not set correctly.

This deficiency can be overcome to some extent for some applications with the fake-hwclock module and SNTP where the RPi is always connected to a network.

The standard scheduling daemon cron does not run tasks that were missed because the system was not running at the time they were scheduled. It is a significant shortcoming that has been overcome by adding another element, anacron, which wraps the cron tasks and is scheduled by cron and at startup. All of this is very dependent on correct clock time, and for RPi systems that lack a hardware clock (the out of the box hardware), the system time can be quite wrong at the time anacron is scheduled as part of the startup procedure.
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Real time clock for Raspberry Pi

One of the shortcomings or RPi for (m)any serious applications is that it lacks a hardware clock so when it starts, the clock is not set correctly.

This deficiency can be overcome to some extent for some applications with the fake-hwclock module and SNTP, but this is not a solution if the RPi is not always connected to a network time reference.

One solution is a real time clock module such as the DS1307, or better still the DS3231. The latter has an internal crystal with 2ppm (5s/month) accuracy from 0-40° which is much better than typically achieved with a DS1307 (which is dependent on the external crystal). Continue reading

APRS: how many digi hops to make it to APRS-IS

APRS is almost exclusively source routed, and depends greatly on sensible path configuration by each and every user.

This is one of those cases where individuals acting independently and rationally for their own personal behave contrary to the whole group’s long-term best interests by depleting some common resource (the tragedy of the commons).

Increasing the available WIDE path length does expose a station’s packets to more iGates, but the average effect of everyone following that strategy is to literally exponentially increase channel busy as the available hops is increased. Continue reading

APRS test drive – 20140930

A short test drive was conducted to evaluation APRS effectiveness in capturing a motor vehicle journey of about 30km.

Google Earth googleearth 30/09/2014 , 13:28:39

The test area is between two digipeaters spaced almost 40m apart, so within the overlapping coverage area of VK2RHR-1 about 17km NW of the test area, and VK2AMW-1 about 17km SW of the test area.

Three position capture devices were used:

  • APRS on 2m (blue track on the maps);
  • APRSdroid (green track on the maps);
  • Bushnell Backtrack Detour (stand alone GPS logger) (red track on the maps).

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Synthetic fibre rope for antenna rigging

Fibre rope has applications in antenna rigging, typically for halyards and tails to support the ends of wire antennas such as dipoles. The use of fibre rope for guying applications has issues due to shrinkage when wet.

Much is made of the ‘best’ fibre rope for these applications, and the almost universal answer is black Dacron (Polyester) in small sizes from 2.5mmm to 6mm diameter. The smaller sizes are usually a braided construction, commonly known as venetian cord. Claims are that the Polyester rope is strong, UV proof and rot proof. Whilst Polyester rope is resistant to mild acids and alkalis, it is damaged by strong alkalis (such as might develop when an alkaline solution dries on the rope). Continue reading

Headless aprx APRS server – RPi packages

In earlier articles I documented a trial of aprx v2.08r593:

Encouraged by Kenneth Finnegan who merged some fixes by WB4XO (which still didn’t work properly), I set about resolving some problems.

Further fixes and some enhancements have been pushed to the source fork at owenduffy/aprx. This was forked from PhirePhly/aprx which in time may pull the changes.

You can browse owenduffy/aprx for brief descriptions of the changes.

Recent Debian packages for RPi based on my fork have been uploaded to http://owenduffy.net/files/aprx/ .

Mostly electronics…