Dialing in to ESC Minneapolis 2017

September 01, 2017

Max The Magnificent-September 01, 2017

In my previous column, I described how I'd come to run across a capriciously cunning display device called a Lixie. Created by Connor Nishijima, this is a LED-based interpretation of a Nixie tube. I closed that column by saying:

The reason I'm waffling about all of this here is that I will be attending the forthcoming Embedded Systems Conference (ESC), November 8-9, in Minneapolis, and I plan on bringing a Lixie to show to my chums (and anyone else who doesn't get out of the way fast enough).

I've now taken delivery of 12 Lixies, which will serve as the primary display mechanism for a project I'm calling a Countdown Clock. These will be grouped in pairs that will display the years, months, days, hours, minutes, and seconds remaining until the start of the event in question. I'm still debating with myself how to present the Lixies -- either as a single row containing six pairs, or as two rows each containing three pairs.

Now, suppose we wish to use the Countdown Clock to mark my 100th birthday, for example. This momentous occasion will occur on May 29, 2057 (it might be best to mark your calendar now). I certainly don’t want to be getting up early on my birthday, so let's set the kickoff time to be exactly 10:00 a.m. This means that we will need some way to enter 57 05 29 10 00 00 to represent the year, month, day, hour, minute, and second, respectively. Once this date has been locked in, the clock will use the current day/time to determine how long there is to go, and it will then start to display the number of years, months, days, hours, minutes, and seconds remaining.

So, the next question is how we are going to enter the date of the target event. In fact, I'm planning on using multiple mechanisms. For ease of use, I'll use my smartphone to control the Countdown Clock via Bluetooth. I'm thinking of a simple app that allows me to add, delete, and modify multiple events.

But I also want to provide an entry mechanism that provides a little more panache and joie de vivre, as it were, and few things provide more style and chic than a retro rotary telephone controller.


(Source: Max Maxfield)

The controller shown above is a restored Western Electric #7 Dial for 500 series telephones (the model 500 telephone series was the standard domestic desk telephone set issued by the Bell System in North America from 1950 through the 1984 Bell System divestiture.) I acquired this little beauty from the Old Phone Shop website.

If we look at the back, we see two switches. The one in the center closes when you start to dial an individual number and opens again once you've finished. The one on the right opens and closes to generate a series of pulses corresponding to the number being dialed.


(Source: Max Maxfield)

In the case of North American phones, one pulse corresponds to the number '1', two pulses to the number '2', and so on up to 10 pulses for '0', but different countries used different schemes, so make sure to check things out if you plan on doing something like this yourself.

I connected the terminals from the right switch up to a 5V supply via a 10KΩ resistor, hooked it up to an oscilloscope, and dialed the number '7'. The result was seven pert positive-going pulses as shown below.


(Source: Max Maxfield)

Each pulse has a duration of close to 100ms (60ms at 5V and 37ms at 0V). One thing that surprised me is just how regular these pulses are. Also, even though I zoomed in, I was surprised to see that there is no discernible switch bounce (I wonder how they managed that).

Will you be attending ESC Minneapolis yourself? If so, I'm planning on bringing my telephone dial for "show and tell." You'll be amazed how good it feels in use -- possibly more so if you actually used one when you were younger without thinking much about the underlying technology.

I'll also be presenting two sessions: Advanced Technologies for 21st Century Embedded Systems and Building an Artificial Brain. Happily, both of these talks will be in the ESC Engineering Theater, which means anyone can attend so long as they are flaunting a Free Expo Pass, but you do have to register. Hopefully I'll see you there. I'll be the one in the Hawaiian shirt. As always, all you have to do is shout "Max, Beer!" or "Max, Bacon!" to be assured of my undivided attention.

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