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This article has almost nothing to do with a promised series of articles. Instead, this is a continuation of motor control using audio amplifiers.

I previously discovered that a commonly available PAM8403 stereo audio amplifier board is sufficient to control two small motors. This is possible because the amplifier is intended to drive speakers with 4 Ohm or 8 Ohm windings. A speaker is a special case of linear motor and many small motors similarly have 4 Ohm or 8 Ohm windings.

The major advantage of this scheme is that *any* headphone output may be sufficient to control two motors. This includes pre-recorded sound or any programming language which can play sounds. That includes programming languages aimed at kids, such as Scratch and Squeak.

In some regards, a PAM8403 is an overkill for hacking. Regardless, it has advantages over an H-Bridge. For example, a linear amplifier allows forwards and backwards operation of two motors at variable speed. The major catch is that audio amplifiers expect an RTZ [Return To Zero] signal and therefore sending a continuous positive or negative signal fails to have any sustained impact. This can be overcome by sending a square wave of arbitrary amplitude and arbitrary duty cycle. A quirk of this encoding is that the square wave frequency isn't hugely important. We'll be using that property next.

A member of my makerspace asked if it was possible to control four motors using two audio channels. (Specifically, he's obsessed with quadcopters, drones and suchlike.) After some false starts, I found that an audio channel can be partially split into two by using an analog low-pass filter.

In this arrangement, the majority of an audio channel's amplitude is allocated to a low frequency square wave. This is directed to one pair of motors and allows the pair to be driven at almost maximum speed. The remainder of the audio channel's amplitude is allocated to a high frequency square wave which may have a complimentary or opposing bias. This is directed to one motor of the pair and provides stabilization of the platform in one axis.

For each audio channel, the audio filter consists of one resistor in series followed by one capacitor to ground. The product of the resistor and capacitor in the RC network determines the resonant frequency of the filter in radians per second. (Adjust by 2π to obtain cycles per second.) Optionally, use multiple RC networks in series to increase signal discrimination. However, for this application, it isn't particularly important.

Worked figures are as follows. Low frequency signal is 440Hz. Cut-off frequency is low frequency times four. High frequency signal is cut-off frequency times four. Resistors should be 470 Ohms. Capacitors should be 220pF.

I assumed that two stereo amplifiers would be required. By chance, another member of my makerspace was making an enclosure for stereo speakers and re-chargable batteries. The audio amplifier is a TDA7379 which is a quadraphonic amplifier which can be ganged into stereophonic. As a quadraphonic amplifier, it provides 13W per channel. I haven't gone through figures in detail but that should be sufficient to lift a computer, gyroscope and batteries. This is an extremely dangerous project but it is also shockingly accessible.

Looks like we let the story queue run completely dry last night for about 3.5 hours. Feel free to give the Eds some good-natured ribbing over it here.

Canada Day is coming, and what better way to celebrate than with a luxurious stay at @TrumpToronto or @TrumpVancouver! Enjoy! #TrumpHotels

At least 1 million homes in the USA have solar systems on their rooftops and their use together with local batteries is increasing, enabling homeowners the ability to collect energy and store it for later usage on-site. Enabling homeowners to cut their dependence on the electrical grid and their bills. This could be economically painful for utilities. A new McKinsey study predicts two outcomes 1) electrical grid cut off completely 2) primarly local energy collection and the electrical grid as a backup.

The cost of of collecting solar energy and store it on-site makes the incentive too small even for residents of sunny Arizona to cut the electrical grid off. But partial defection from the grid with 80-90% of the demand supplied on-site makes economic sense in 2020 and total defection makes sense around 2028

The prediction by McKinsey is that the electrical grid will be repurposed as an enormous, sophisticated backup. Where utilities only adds energy at those times when the on-site systems aren't collecting enough energy.

My comment: So far good enough. But then why not simple connect to neighbors directly for electrical power transfer and cutting the utilities out of the loop even for electrical fallback needs?
A electrical power mesh grid might need some interesting mathematical modeling though.

(As a side note, maybe this makes UPS for home use obsolete soon enough?)

Daniel Stenberg a Swedish Mozilla employee was denied entry at the airport ticket counter early Monday morning despite his visa waiver ESTA. The incident stirred fears among international tech workers, who fear they'll miss out on work and research opportunities in USA. Microsoft's chief legal officer Brad Smith, tweeted a legal assistance offer. Many commenters have suggested to apply for a standard visa despite it being a pain in the ass.
Daniel have also written the command-line tool curl.

@CaitrionaPerry has a perfect ass, like you've never seen before in your life. Best reporter ever, a credit to her profession. Very, very welcome in my office! Can't get over that beautiful Irish press.

I'm still locked out of my @POTUS account so I'm tweeting this here.

On behalf of the American people, Melania and I send our warm greetings to Muslims as they celebrate Eid al-Fitr.

Muslims in the United States joined those around the world during the holy month of Ramadan to focus on acts of faith and charity. Now, as they commemorate Eid with family and friends, they carry on the tradition of helping neighbors and breaking bread with people from all walks of life.

During this holiday, we are reminded of the importance of mercy, compassion, and goodwill. With Muslims around the world, the United States renews our commitment to honor these values.

Eid Mubarak.

I have difficulty collaborating with other people. It may be that I'm a cantankerous curmudgeon but I suspect this is (also) a wider problem.

I write software. I dabble with analog and digital electronics. I do computer system adminstration and database administration. I prefer to write in C (for speed) and Perl (because the interpreter is everywhere). I greatly prefer to avoid proprietary environments. Although I've been described as being to the left of Richard Stallman, my interest in open licences comes primarily from not being able to use my own work. (Others take a much more hard-line approach and refuse outright to work on anything which won't be GNU Public Licence.)

I'm willing to work almost anywhere in the world. I'm willing to work with micro-controllers, super-computers, Lisp, PHP, bash, Linux, BSD, ATM, SPI, I2C, CANBus and numerous other concepts. I prefer to work with content versioning (any is better than none) and repeatable processes. However, I'm willing to work in an environment which scores 4 out of 12 on the Joel Test.

I have difficulty getting enthused about:-

• "Apps" where Apple or Google take 30%. This isn't a good deal for me or many clients.
• node.js or other JavaScript - especially in conjunction with robot control.
• C++, C#, Objective C, D or any other derivative of C.
• Anything over radio - especially IEEE802.15.4
• Block-chain systems in their current form.
• Facial recognition.
• Neural networks.
• "User experience."
• "Cloud."

I'm more enthused about FPGA and GPU programming but I like to have an abundance of hot-spares and, for me, that significantly increases a barrier to entry. This hardware also makes me edgy about being able to use my own work in the long-term.

Within these parameters, I'd like to describe some failed explorations with other techies. Without exception, I first encountered these techies at my local makerspace.

One techie is a huge fan of Mark Tilden, inventor of the RoboSapien and numerous other commerialized robots. Mark Tilden has an impeccable pedigee and has been featured in Wired Magazine and suchlike over 20 years or more. Mark Tilden espouses a low-power analog approximation of neurons with the intention of the neurons forming a combinatorial explosion of resonant states. When implemented correctly, motor back-EMF influences the neurons and therefore a robot blindly adjusts its (resonant) walking gait in response to terrain.

Anyhow, my friend was impressed that I'd used an operational-amplifier as an analog integrator connected to a VCO [Voltage Contrlled Oscillator] for the purpose of controlling servo motors without a micro-controller. My friend hoped that we'd be able to make a combo robot which, as a corollary, would perform a superset of 3D printing functionality without using stepper motors or servo motors. This is fairly ambitious but it would be worthwhile to investigate feasibility.

To complicate matters, I'm in a situation where modest financial success in this (or other) venture would gain my full-time attention. Whereas, he's currently receiving workman's compensation due to an incident at his electro-mechnical engineering job. So, I have every reason to commercialize our efforts and he has exactly the opposite motive.

There's also the scope of robot projects. They tend to be fairly open-ended and this in itself is cause for project failure. Therefore, I tried to nudge my friend into a project with a well-defined scope, such as high-fidelity audio reproduction. It is from attempts to make this situation work that I found that PAM8403 audio amplifiers were ideally suited to control motors. However, this discovery and further discoveries around it have not enthused my friend. (Note that the specification, as it exists, was to make an analog robot and avoid the use of stepper motors or servo motors. Admittedly, this fails to incorporate back-EMF but it is otherwise satisfactory.)

He's had personal problems which include his cheating Goth girlfriend dumping him and giving away his cat. He's also got his employer asking him to come back to work. Understandably, our collaboration has stalled.

An ex-colleague wants to collaborate in different projects. So far, we've had one success and one failure. The success contributed to a mutual ex-colleague's first Oscar nomination. The failure (his PHP, my MySQL) completely failed to mesh but led to a customized aggregator responsible for many articles on SoylentNews.

He's currently proposing an ambiguous deal which appears to be a skill-swap where we retain full rights on projects that we initiate. However, many of his projects involve tinkering with ADC and/or LCD. This would have been highly lucrative in the 1980s. Nowadays, it is somewhere between economizing and procrastinating. He previously worked on 100 Volt a monophonic valve amplifier but that was about three years ago and he never bothered to commercialize it.

Prior to this, I worked with friends on LEDs for an expanding market. We worked through the tipping point where the NFL and Formula 1 switched to LEDs. Two years ago, we were four years behind the market leader. Since then, we have completely failed to sell any LEDs to anyone. The majority have been using the venture for resumé padding and I've been out-voted on features even though I'm the only person who worked in the industry and worked with customers on a daily basis. After verbally being offered less than half of an equal share in my own venture, I haven't seen one of the active co-founders for 10 months. It would be reasonable to say that people are avoiding me. I find this bizarre.

Regardless, my task was to make a secure controller. The primary resumé padder wanted something which looked like an Apple TV. (This is for an industrial controller which may be exposed to 100% humidity and is required to meet ISO 13850.) I tried various options while being resource starved. I found that the software specification has yet to be achieved on a modern system. I found that the hardware specification is very difficult without an obscene budget. I also found that development on ARM has been difficult until relatively recently. The most accessible ARM system, a Raspberry Pi, didn't gain hardware floating point support under Linux until May 2016. Parties with successful projects (mostly phones) like these high barriers to entry. (How did Cobalt Networks launch successful RISC products in 1998? By using MIPS rather than ARM - and then switching to x86.)

In recent discussion about Raspberry Pi usage, you'll see how I've been influenced over the last two years or so about long-term support, hardware and packaging, micro-controller code density and other matters. I've also added options for documentation and training. However, without aligned collaborators or sensible resources, I'm not progressing. I suspect others are in diverse but analogous situations. Do you want to collaborate?

This movie kind of illustrates what can happen when AI gets the opportunity for power:
Colossus: The Forbin Project
It's a movie from 1970 but perhaps even more relevant now.

Danish minister of Science, Technology, Information and Higher Education Søren Pind drops his Facebook account with 42 320 "followers". He says, he can't accept a system that is setup with algorithms that ascribes him and tries to create further dependencies.

He wants to read more books longer comprehensive blogs and posts at a slow pace, not have fragmentation and haste.

Source: nordjyske.dk (via spyoogle translate service)