Late Adopter of Things

After the dusty relics of recent posts (tubes, slide rules, etc) it is time for something more 'on trend'...

I was pleased to meet Richard, g0vxg, at the recent "Radio Active" rally and it was he who told me I should be checking out Expressif''s ESP8622. Accordingly, the notorious late adopter put in an order via the internet.

The devices have been making their way toward me ever since and the proverbial 'slow boat' just docked...

As you can see, I chose to buy some ESP8266s with a mounting PCB, which allows for the unit to be mounted via 0.1 inch headers on my beloved solderless breadboards for simple prototyping. This extra expense was no expense at all, as the whole enterprise cost less than a pint of best.

The ESP8266 (for those who cannot be bothered to follow hyperlinks) is a WiFi chip with an integrated micro, which can be programmed via the Arduino IDE. It has its own (limited) I/O capabilities. It has been described by some commentators as the Arduino killer. Obviously - I had to try it - but in order to try it, you need to program it...

Of course, given my purchase, I could plug it into a solderless breadboard. But I decided i) that I didn't want to commit a breadboard and ii) that I needed something a little more permanent.

So...

A scrap of perfboard (which had been rejected at work because it had been ordered in error, by somebody who thought it was stripboard - I rescued it from the trash can and gave it a loving home) gives, in turn, the ESP8266 module a home. Also, there is provided the two push-buttons, required to pull the ESP8266's Reset and GPIO0 pins to ground and manually cause it to enter the FLASH mode, in which it can be programmed using a USB to TTL module, which plugs in at bottom left, according to the recipe that can be found all over the 'net. The ESP8266 can be powered either from the programming module's computer or by the pair of AA batteries in the holder at the right of the photo (the ESP8266 is a 3v3 device).

However, pressing buttons is very yesteryear - so I was pleased to find a description of a simple circuit on www.arduinesp.com which also is implemented on the board above. The entire 'programming' side of my board is as described below...

You change between 'manual' and 'automatic' programming by inserting links on the jumper. I found the little twin transistor circuit worked perfectly as described on www.arduinesp.com - apart from one additional step...

It was necessary to set the Reset Method to 'nodemcu' in the 'Tools' drop down menu of the Arduino IDE:

Once this is understood, you can go ahead and plug in your FTDI board and get coding within the familiar Arduino development environment.

Here you see the little red USB to TTL board, with an extra flying lead to connect to the 'Ready to Send' and 'Data Terminal Ready' lines (the latter is also available on the edge-facing pins - but I did it this way for convenience). The little solderless breadboard hosts an LED for the inevitable 'blink' programs which form the subject of microcontroller programming 101...

There is a blink example described on www.arduinoesp.com - which is a modified version of the blink example in the built-in Arduino resources. But what's the point of this? You might as well just use an Arduino! To get added value from the ESP8266, you need to start to exercise the WiFi functionality. Fortunately, doing that is super-easy...

I found a great tutorial on www.openhomeautomation.net and - within minutes - I was able to hack it to control the LED in the photo above over the internet from a browser on my phone...

The browser page is served by the little ESP8266...

This application is only for local control (i.e. over your own WiFi network) but www.openhomeautomation.net goes on to explain how to extend control over the entire internet.

This is incredible - here we have a device, which costs less than a beer, which can be used to do all sorts of neat stuff, of which controlling an LED is really just the beginning. Applications limited not by cost or size (Richard's server, including its power supply, was hiding in a matchbox). Not limited by technology at all - just by imagination.

Genuinely exciting.

...-.- de m0xpd

ECL86 Amplifier Test

Every once in a while, life in general and my shack in particular gets into such a mess that I can hardly breathe. At times like these my long-suffering XYL comes to my rescue and helps me to tidy things up. We had a bit of a tidy today and I found some goodies - including the old ECL86 AF amp prototype and a dummy load for AF amplifier testing.

After the tidy up was completed, I treated myself to a little gentle play at the bench, by hooking up this little tube amp to the 'new' HT supply. First (after fixing all the broken wires) I just listened to it, then I connected it to the dummy load...

Just as with RF experiments, cheapskate audio engineers find it difficult to get hold of perfect dummy loads. In the case of AF, there isn't a problem with inductance (as the frequencies are so low that wire-wound power resistors can be used for amplifier testing to first order of approximation, at least). However, exactly as we can't find 50 Ohm resistors straight out of the E series for RF, there similarly aren't 8 or 16 Ohm resistors to emulate ordinary nominal speaker loads.

Fortunately, 10 Ohms is close enough (and we don't get standing wave patterns on speaker cables, HI HI), so that's what I've always used to model an 8 Ohm speaker...

Note that as well as the ordinary 4mm binding posts, my 10 Ohm dummy load has a BNC socket, which allows me to read the voltage across the load. This allows me to simply measure - for example - the voltage gain of an amplifier, which I took the opportunity of doing for my little toy triode/pentode amp...

It offers about 32dB of gain over a pretty narrow bandwidth, which is fine for the voice applications for which it was conceived.

Now I have to tidy away this little amp - which is making the place look a mess and getting in the way of any real work. Then I have to go and say 'thanks' to the XYL.

...-.- de m0xpd

Beer and Filters

I'm planning to show off my nice old Pickett N-515-T to some students in a few days time. I think I'll need a hook to get them interested and one sure way of attracting the attention of engineering students always used to be beer...

As is well known, empty (or part-empty) beer bottles, exhibit a nice acoustic second order resonance, analogous to the electrical resonance of an LC filter...

Reflecting the analogy, the resonant frequency is determined by exactly the same equation  I presented in the recent post on my beautiful old slide rule, where the 'capacitance' is the acoustic compliance of the volume of air in the body of the bottle and the 'inductance' is the acoustic mass of the 'slug' of air in the neck.

The equations for these parameters are...

in which rho is the mass density of air and c is the speed of sound.

Air is surprisingly 'heavy' stuff - such that its density at the ordinary temperatures and pressures in which you're likely reading these words is around 1.22 kg per cubic metre and the speed of sound is around 340 metres per second. V is the volume of air in the 'body' of the bottle, l is the length of the neck and S is the cross-sectional area of the neck.

There are a bunch of other details, which I'll not bore you with - such as the reason for saying 'acoustic' compliance above. Also, the length l needs an 'end correction' (an additional length), to account for the radiation of sound from the open end of the bottle and the cross sectional area of the neck is not constant in the Bud bottle pictured above, such that specifying S isn't easy!

Taking a look at the bottle through half-closed eyes (and noting it was specified on the label to hold 330mL), I came up with some very ROUGH ESTIMATES of V=295 e-6 cubic metres, l=0.09 metres and S=3.14 e-4 square metres.

These produce the following equally rough values for the 'capacitance' and the 'inductance' (don't worry about the units):

C = 2.09 e-9
L = 347

I tried to solve for the resonant frequency of (the air inside) the Bud bottle on the Pickett N-515-T (I wonder if that's been done before?) using exactly the same steps as previously described.

We start with the rough estimate on the Decimal Point Locator...

First, we find the capacitance of 2090 pF, since there isn't a nanoFarad scale (I've indicated 2000 pF by my green line and red circle)...

then we move the slide until the 2090pF lines up with 347 H on the slide. This is difficult to do, as 347 Henries would be one big mother of an inductor, so the scales didn't run that high, stopping at 100H.

Fortunately, there's clear space above 100 Henries and we can easily see how the logarithmic scale works so, extrapolating from the decade 10:100, we can 'imagine' the decade 100:1000 (which I've labelled in blue on the photo below) and position the slide approximately...

Then, we should be able to read off the resonant frequency from below the arrow...

it is around 200 Hz.

For more accuracy, we can multiply together the 'inductance' and 'capacitance' to find the LC product...

 
 to get 7.25 (e-7) and set the hairline of the cursor over this value on the cursor on the 'H' scale...

The resonant frequency is directly read from the D scale to be around 187 Hz.

Blowing over the beer bottle, in traditional bar-room style, whilst running a tuning app on the iPad, revealed an actual frequency of 196 Hz ...

so this model - and the rough estimates of sizes - was reasonably accurate.

The bottle is (as many will know) an instance of what is called a Helmholtz resonator, after German physician and physicist Hermann von Helmholtz. Hermann was way too dignified to blow over bottles in bar rooms - here's an image from my copy of his 'On the Sensations of Tone...', showing his equivalent of the Bud bottle...

He even arranged a nice little 'Guttapercha' tube to direct the blowing!

It is nice to see that the Pickett N-515-T is good for more than electronics. I wonder if many other folks have done acoustics on it - or taken it into the bar?

...-.- de m0xpd

A New Book

Today, on this anniversary of the admission of Ohio as the 17th State of the Union,

I’m pleased to announce a new book, ‘getting there’

The book tells – superficially – of my experiences at last year’s QRP-ARCI Four Days in May convention in Dayton, Ohio.

Whilst it is told against the background and context of amateur radio, THIS IS NOT A TECHNICAL, ‘HOW-TO’ BOOK, so please don’t buy it expecting to find a series of schematics of radios or computer programs!

Instead, the book talks of my experiences of preparing to go not only to Dayton, but also on a longer journey of exploration... back to my old home in Wyoming.

The words of my book are about my journey last year – but between the lines the book tries to speak of bigger journeys and the people we meet along the way.

In my case, many of these meetings have occurred within amateur radio, and the little book is propelled by my special relationships with three people who you will know, by reputation at least: g4ilo, g3rjv and n6qw...

Of these friends, George, g3rjv, has written a Foreword for the book. I’ll leave him to do some ‘marketing’ by quoting from his Foreword...

“Paul’s entertaining, and often amusing, book 

gives a lively account of people and radios.” 

‘getting there’ is available from Amazon.co.uk, Amazon.com and all good booksellers!

…-.- de m0xpd