On Thevenin’s theorem – #2

On Thevenin’s theorem looked at a simple source network to demonstrate some key characteristics and limitations of Thevenin’s equivalent circuit.

The example network used was linear in V,I for all V,I combinations possible. Let’s now look at a network that is not linear for all V,I, but is sufficiently linear over a sub range to be usefully modelled using Thevenin’s equivalent circuit.

Black Box for discussion

For the purpose of discussion, we have a Black Box with just two terminals and is a source of DC voltage and current, and the internal implementation is hidden from us.

A series of measurements is made with different load resistors attached and the voltage and current at the terminals is recorded and plotted uniformly stepped currents.

The V,I characteristic is clearly non-linear, but on closer examination there are two fairly linear regions, from 0.008 to 0.060A and 0.08A to 0.1A. It is a device that is usually used in the region below the knee, and for our application, let us concentrate on 0.008 to 0.030A. Continue reading On Thevenin’s theorem – #2

Last update: 26th December, 2018, 6:18 PM

A third test of the FA-VA5 antenna analyser

I recently acquired a FA-VA5 antenna analyser.

Whilst preparing A first test of the FA-VA5 antenna analyser, issues were noticed with the user interface design / implementation. I stated in a later article that The matter of the clumsy / unproductive user interface will be explored more at a later time.

This article introduces a short video demonstration of the frustrating / unreliable user interface (UI) in firmware v1.08 where buttons do not seem to operate intuitively and consistently.

The video shows that whilst the up down buttons seem to work reliably and consistently in ‘menu’ mode, they do not do so when trying to adjust the frequency. Continue reading A third test of the FA-VA5 antenna analyser

Last update: 16th May, 2020, 7:30 AM

The first seven days of Exetel broadband Internet access

We have had wired broadband service delivered to these premises for almost ten years, supplied by five vendors: Telstra Bigpond, iiNet, Amaysim, Southern Phone and now Exetel.

The change from Amaysim was at Amaysim’s choice, they decided to quit the wired broadband business stating that they could not make a profit, and they sold their customer base to Southern Phone.

Southern Phone was unable to deliver the VOIP service we have had for many years through all of those broadband suppliers, so we churned to an Exetel “Standard Plus” service.

Cutover

The cutover was badly coordinated, there was a 12 hour outage, and I had to phone Exetel (yes, wait in the interminable queue to try to get the modem PPP credentials, it had DSL service and was routed to Exetel, just needed the authorisation details for Exetel).

Telecommunications providers are all about strong procedures for handling usual business, and this part of the business is known as provisioning. The events with Exetel hint that their provisioning processes are not sensitive to churning an existing NBN connected service which should be done to minimise disruption, including advising the logon credentials, doing it when their support desk is open, holding if the customer needs a new modem etc. This is the bread and butter of the business, but a FAIL to Exetel on this occasion.

First impressions are lasting ones… so how do they come back from that start?

Service levels

I have an expectation that “I want it to deliver most of the rated speed, most of the time during the hours that I want to use it”.

As a result of behaviour of the industry, the ACCC gives some guidance on terms used to advertise a service, and a service expectation.

Essentially they say:

Standard Plus Evening Speed—plans using this label will deliver a minimum speed of 30Mbps during the busy period. This plan would be suitable for a higher usage profile (e.g. streaming an ultra-high definition movie and streaming music on one or more other device during the busy period)

 

So on that measure, how well did they perform?

Above are the results of file transfer tests conducted automatically, the above are filtered for those in the ACCC’s defined “evening hours” on which they base their service level enforcement. All + symbols in the pink area break the 30Mb/s minimum. Continue reading The first seven days of Exetel broadband Internet access

Last update: 24th February, 2019, 1:09 PM

ISP adapter for Arduino Pro Mini / Pro Micro

I have started using Arduino Pro Micros recently, and sourced inexpensive clones from China.

Experience is that all manner of inexpensive small microcontroller modules from China are likely to have issues with the bootloader: it isn’t there, it is back level, not suited to the actual clock speed.

I have come to routinely install a current / known / working bootloader to avoid wasting time down the track.

The Pro Micro does not have an ISP header, and the QFN package does not suit a chip adapter, so the next option is an adapter that can connect to the board with no pins, male or female headers, top or bottom.

Above is an adapter built on a small piece of Veroboard. If you are ging to copy it, make it one row of holes higher. I did initially, and in a miscount of rows, I incorrectly removed the top row. The black mark identifies the pin 1 of the Pro Micro, and the adapter connects to the side with the /RST pin.

 

The headers on the adapter engage JP6, preserving the pin ordering, pin 1 to the black mark on the veroboard. The adapter does not use or connect to JP7.

Continue reading ISP adapter for Arduino Pro Mini / Pro Micro

Last update: 26th September, 2023, 11:49 AM

Yet another change of Internet broadband access

We have had wired broadband service delivered to these premises for almost ten years, supplied by five vendors: Telstra Bigpond, iiNet, Amaysim, Southern Phone and now Exetel.

Download speed

Download speed is an important performance characteristic, and fairly quantifying it is a challenge.

If I were to express my service expectation as “I want it to deliver most of the rated speed, most of the time during the hours that I want to use it” we can express that by better defining the three terms:

  • most of the rated speed;
  • most of the time; and
  • the hours that I want to use it.

Most of the rated speed

Let’s consider that most means 80%, so the critical value of speed is 80% of the rated speed, eg 80% of 12Mb/s is 9.6Mb/s.

Most of the time

Let’s consider that most means 80%, so the critical value is 80% of the time.

During the hours that I want to use it

I sleep at nights, and use the Internet variously during the day, the most important times for service to be adequate are from 06:00 to 20:00.

Critical speed requirement

Capturing the foregoing, I could write “Download speed must exceed 80% of the rated speed, 80% of the time between the hours of 06:00 and 20:00” each week.

This is known as a Service Level specification.

Statistically, this is stated as the 20 percentile speed measured between 06:00 and 22:00 over a week must be greater than 80% of the rated speed.

Test results

A realistic simple HTTP download is scheduled every half hour, and the effective download speed is recorded. This data has been gathered for many years.

Over the nearly 10 years of service, the rated speed has varied, 8, 12, and 50Mb/s at different times. To compare these, the speed in any one observation needs to be normalised to the applicable rated speed, so for this purpose speed is calculated as a percentage of the applicable rated speed.

Telstra

Above is a plot of the measured speed over a period of many years. Continue reading Yet another change of Internet broadband access

Last update: 24th February, 2019, 1:10 PM

IoT – exploration of LoRa – part 3

This series documents a set of experiments to explore LoRa for a telemetry application. Note this is simple multipoint to point LoRa, it does not use LoRaWAN.

IoT – exploration of LoRa – part 1 outlined a simple direct RESTful submission to Thingspeak from the LoRa – Wifi gateway.

IoT – exploration of LoRa – part 2 outlined a simple RESTful submission to Node-Red from the LoRa – Wifi gateway.

This article describes a direct MQTT submission from the gateway. In this case the gateway converts the binary LoRa payload into more friendly MQTT key,value pairs.

The block diagram above shows the information flow between the main elements. Continue reading IoT – exploration of LoRa – part 3

Last update: 26th March, 2019, 12:51 PM

IoT – exploration of LoRa – part 2

This series documents a set of experiments to explore LoRa for a telemetry application. Note this is simple multipoint to point LoRa, it does not use LoRaWAN.

IoT – exploration of LoRa – part 1 outlined a simple direct RESTful submission to Thingspeak from the LoRa – Wifi gateway.

This article introduces an intermediate flexible and extensible Node-Red flow.

The block diagram above shows the information flow between the main elements. Continue reading IoT – exploration of LoRa – part 2

Last update: 5th December, 2018, 6:19 PM