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first stab at a first world problem
Sunday, November 1 2015
Daylight savings time is always welcomed when it first arrives in the morning, especially for people like Gretchen who work on Sundays. But when sundown comes shortly after 4:00pm, it adds to the dreariness that this time of year is already signaling. My Ahmed Mohamed clock is based on an Atmega328 whose 32 kilobytes of flash ROM firmware is nearly 70% used, and yet it has no automatic provision to adjust to and away from Daylight Savings Time, adding somewhat to my confusion about what time it was.
Not many years ago, landline telephones were useful ways to reach out to friends, governments, and businesses to set up appointments, make dates, or just chat about stuff. Indeed, as recently as the late 90s, this was the main way this remote communication was conducted. But in recent years (accelerating maybe five or six years ago), landlines have become the province of hucksters, spammers, and the kind of people who get Ben Carson to endorse their products. These days, caller ID is an essential part of landline service and nobody under fifty would answer a call before first finding out who it is coming from. This dramatic deterioration in the value of landline service must be especially crushing for the elderly, who are stuck in their ways and likely to still be answering their landlines like they did back in the 1980s. I have a feeling there are legislative fixes available for this problem, but such job-killing regulations are a pipe dream while a plurality of voters are driven to madness either by the reality of gay marriage or the existence of a president who is not white and male. It's admittedly a first world problem, but it's a problem nonetheless.
One solution would be to dump our landline and rely on cellphone service (which is more heavily regulated), but in our area the only broadband available is DSL, which is difficult to extricate from a package that includes a landline. Also, I don't have a cellphone, and I much prefer the voice quality delivered by a landline. Often times I can barely understand what is being said even by friends if part of the link involves a cellphone tower (and forget about it if the caller is a tech job recruiter who learned English in Calcutta).
A little less than two years ago, the solution I tried was something called a T-lock Call Blocker, which supposedly stores phone numbers from known spammers and automatically hangs up on them. Unfortunately, though, neither Gretchen nor I could get the thing to work. Its caller ID functionality failed to identify the phone numbers of shitheads even when our phone managed to do so. Clearly, what we needed was a device that could be tinkered with and configured. That sounds like a job for an Arduino.
So this evening, I began work on yet another Arduino-based project. This one will attempt to read caller-ID information from a ringing telephone line and then use that information to, in many cases, automatically answer and then hangup the phone. It might also do things like log phone numbers with timestamps so that they can be mined for patterns (because Big Data!).
Today's work involved creating the rudiments of a phone interface. Phone lines are prone to high voltage swings, transients (some caused by lightning), and are controlled by stodgy, impersonal bureaucracies (who nevertheless allow hucksters and spammers to proliferate on their network). To condition phone signals for interpretation by five-volt logic, I had to isolate them using capacitors, a resistor, a 1:1 audio transformer, and a pair of zener diodes connected back-to-back. The design was mostly a simple one I found online, with the zener diodes suggested by this very useful page. Most of the parts were salvaged from old modems and telephones, which are rich in precisely the values of parts that I needed. Eventually these conditioned signals will end up being interpreted by a EM92547B FSK decoder, which will pass the data onto some sort of low-end Arduino for further interpretation, comparison to a known blacklist, and a series of repercussions that will include automatically hanging up the phone.
For linking purposes this article's URL is:
http://asecular.com/blog.php?151101 feedback
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