Computing – Page 4 – owenduffy.net

mpd on a RPi, streamripper and sox

For some years I have run mpd on an early RPi as a media player, and it has worked very well… better as Raspbian improved in robustness. Playback is controlled mostly from mpdroid on our Android tablets or phones. Playlists switches can be automated using cron on the RPi.

Whilst using Telstra Bigpond ADSL for broadband access we have been unable to stream Shoutcasts (“Internet Radio”) without frequent stops and starts rendering it unusable. The 8Mb/s broadband service performed so badly it would not sustain near real time traffic at 200kbps.

With the experience that Telstra does not maintain sufficient capacity to give its customers good service, we chose another provider once NBN access became available. Continue reading mpd on a RPi, streamripper and sox

Last update: 11th October, 2016, 9:07 PM

Adapting a 5V TTL GPS to RS232

5V TTL interface GPSs can be had for about $10 on eBay. They are aimed at the RC market and although the GPS chip is a 3.3V chip, they have a 5V regulator on board and level shifters or 5V tolerant IO.

To use them with APRS you usually need to get RS232 output and to support the common 12V feed on the DE9 connector, the RS-232 / TTL adapter needs to incorporate a 12V/5V regulator.

This article describes a couple of modules that are available on eBay for a dollar or so, and suitable for modification by adding the regulator.

Above left and bottom are two MAX3232 modules that have had a LM78L05 regulator and decoupling cap added to provide for 12V in and 5V to power the MAX3232 and GPS (top right is a Ublox NEO6M).

In the case of the lower module, a track has to be cut to disconnect the pad for 12V in from the existing circuitry.

Last update: 3rd October, 2016, 5:48 PM

Fan controlled by humidity sensor – pre implementation data gathering

This article documents measurements of temperature and relative humidity (RH) over 10 days prior to implementing the fan solution to provide a baseline for designing the Fan controlled by humidity sensor.

A RC-4HC datalogger was used to collect temperature and RH measurements over 10 days which included a range of late winter weather, some rain, some fine clear days. The logger was located at 1.5m above floor level in the shed in a relatively clear spot in the middle of the area..

Above is a chart of temperature and RH. The daily RH peaks are typically between 08:00 and 09:30, and pretty much coincide with the minimum observed temperature. There is clearly a lag from outside temperature which would tend to be minimum a few hours earlier, and a lower minimum (there were plenty of frosty days in the sample set). Continue reading Fan controlled by humidity sensor – pre implementation data gathering

Last update: 22nd August, 2016, 5:43 PM

Time to get some experience with 32bit microcontrollers – some progress

At Time to get some experience with 32bit microcontrollers I wrote that after almost 50 years working with 8bit microcomputers and microcontrollers, I thought it about time to get my hands dirty on some 32bit microcontrollers.

This article reports some work in the STM stream.

I abondoned the ST Discovery board in favour of a low cost basic ST32F103 development board costing about $4 on eBay. The chip is a 32bit microcontroller clocked at 72MHz.

As a learning vehicle, I decided to implement the functionality contained in Arduino thermistor thermometer – a tutorial.

The development environment is Eclipse with the GNU ARM toolchain, a debugger probe, the basic development board, and a 1602 LCD display with I2C backpack and an inexpensive CP2102 USB RS232-TTL interface.

Above is the working trial. The GDB debugger allows On Chip Debugging (OCD).
Continue reading Time to get some experience with 32bit microcontrollers – some progress

Last update: 8th August, 2016, 6:10 PM

Fan controlled by humidity sensor – design technique

This article gives an outline of the process used in designing the Fan controlled by humidity sensor to use my Generic heating / cooling controller design (hcctl).

Arduino thermistor thermometer – a tutorial gave a method for designing a thermometer based on a formula predicting the behaviour of the sensor. This article explains a different approach where that is not possible.

Above is a characteristic from the manufacturer’s data.

The curves to no lend themselves to simple curve fits, so a cubic spine interpolation will be made based on key points from the curve.

Four our purposes, the mean curve (green) is sufficient for design.

Above, the mean curve was digitised to capture the shape of the curve, 17 points were used.
Continue reading Fan controlled by humidity sensor – design technique

Last update: 24th July, 2016, 9:26 AM

A drive test of RTKLIB accurate GPS

Accurate GPS positioning has been of interest in automating data collection in field strength surveys of antennas on HF. To be useful, the positions need to be accurate to 100mm.

RTKLIB is an open source program package for GNSS positioning.

A number of experiments were conducted using a U-Blox LEA-6T assembly with integral small patch antenna (cost ~A$40) and RTKLIB v2.4.3(b8) using a base station feed from Geoscience Australia (with thanks). The test location is about 200km from the reference station at Symonston ACT.

Above, the LEA-6T and a RS-232 to USB adapter are strapped to a roof rack bar with stretch film. The high mounting position gives good view of the sky.

Above is a position plot of about an hour with the vehicle stationary (though in Kinematic mode) beside the house. Sky view was slightly restricted by the house and a line of tall trees to the west.

For the most part the track is smooth, but there is one section where the track in a more heavily treed section is markedly jaggy.

Last update: 23rd October, 2022, 2:35 PM

Micro SD card premature failure

I bought a couple of ‘generic’ micro SD cards on eBay about a year ago. They were not much cheaper than brand name cards, and though only speed 6 rated, were available locally for quick delivery. I have a vague recollection that it might have been a RPi product supplied with NOOBS on it (I have a couple of SD adapters with the RPi logo on them).

These were both used in RPi B systems and worked without fault for the last year, though they are not running full time (perhaps a couple of hundred hours of use).

During a Raspbian sofware update, both cards failed with the same problem, they effectively became read-only cards. Continue reading Micro SD card premature failure

Last update: 26th June, 2016, 12:06 PM

Arduino app to set DS1307 Real Time Clocks

I use a number of implementations of the DS1307 or DS3231 Real Time Clock chip, preferably the latter these days as they are considerably more accurate and compatible with DS1307 code.

In some applications, it is necessary or sometimes just better to preset the clock before connecting it into the application, and the need arises to set the clock ‘stand alone’. The method I have used for this has been clumsy and not as accurate as one might want for the DS3231, so this article describes a new solution.

The solution uses an Arduino as the engine if you like. Above is an Arduino Pro, but a range of similar Arduinos would be equally suitable. ALso pictured are three RTCs, one connected to pins A2, A3, A4 and A5 providing GND, VCC, SDA and CLK respectively. Continue reading Arduino app to set DS1307 Real Time Clocks

Last update: 22nd November, 2020, 4:31 PM

Counterfeit FTDI

I purchased a USB-RS232 adapter which claimed to use an FTDI chipset.

Above is a pic of the device, branded Hexin model HXSP-2108D.

The device delivered pretends to be FTDI to the extent it ships with a FTDI driver disk, uses FTDI’s VID and PID to identify to USB, and works to some extent with separately sourced FTDI drivers, but it does not use FTDI chips. Attempts to read the chip with FTPROG return an empty EEPROM that cannot be programmed… in fact it causes errors in FTPROG.

eBay effectively supports these sellers of counterfeit goods as they require return of the goods to the seller for possible refund, and in this case that would cost about the same as was paid for the goods.

The seller insisted that they would test it and return it or a replacement, carefully avoiding the question of whether it used a genuine FTDI chipset, further reason to not return it as it would just cost good money to get the same counterfeit product back..

eBay harbours counterfeiters, and whilst I have bought plenty of FTDI based devices that appeared genuine (eg using FTPROG), this Hexin product is an incomplete knock off.

Last update: 17th April, 2016, 2:13 PM

Precision GPS experiment #1

This article reports an experiment to evaluate the usefulness of precision GPS for the purpose of location data for automated antenna field strength surveys.

The experiment was conducted with the rover located in a fixed location 13km North of the reference station at Symonston and with very wide view of the sky, about 7:00 am 07/04/2016.

Only GPS satellites were used for the rover.

The software was RTKLIB v2.4.3b8.

The GPS was a UBLOX LEA-6T with a small patch antenna (as sold for small UAVs). The LEA-6T provides binary data as used by RTK for carrier phase measurements. Above is the GPS and a USB-RS232 adapter. Continue reading Precision GPS experiment #1

Last update: 8th April, 2016, 1:16 PM