The Analog Computer Project
The Guru has always been fascinated with different ways of approaching a problem - and here's a unique example. Long before laptops and PC's, before the Apple 1 and the MITS ALTAIR 8800, before the VAX, the UNIVAX, the TRS-80 and the CDC Cyber, there was the Heathkit EC-1 analog computer. A desktop computer weighing close to 50 pounds and having a 30-minute warm-up time. This was a big deal more than a half-century ago.
A view of the unit zeroed-out and ready for programming.
A view of the EC-1 resting atop a lab bench. The unit is in standby mode.
A front view of the EC-1 . The unit is operating in a simple feedback loop.
Another view of the unit performing the unitary feedback test.
Top view of the unit showing the amplifier tubes. We are using original Heathkit tubes.
The operational schematic for the EC-1 analog computer.
Interior shot of the operational amplifier circuits in standby mode.
A simple analog computer program showing the multiplication of 'six' times any value.
The result of 6·(-1.5)=-9.
The Guru's EC-1 was manufactured in 1959. It falls into a very early class of computational devices known as 'analog computers'. As the name implies, an analog computer works by analogy, that is, it draws a comparison between an electric circuit and some mechanical device by applying what is known as the electro-mechanical analogy of physics. It is at heart a differential equation solving machine (specifically ones of the second-order constant coefficient nonhomogeneous variety).
The EC-1 originally retailed for 400 dollars in 1959 and was available as a 'low cost' computer for teaching engineering, physics and mathematics. It was sold primarily in kit form to universities for use in complex problem solution (remember, there were no calculators at that time, just pencil, paper, and slide-rules). It is programmed through a switchboard wiring interface and has no microprocessor or digital logic of any kind for that matter. In an analog computer there are no 'yes' (binary 1) or 'no' (binary 0) answers as is the case with modern digital computers. The answer is provided as a continuously variable voltage output. In this regard, the analog computer represents a problem solution exactly as shown in nature (digital computers always show quantized representations of the same thing). The EC-1 utilizes nine DC operational amplifiers (op-amps) for its computational engine allowing for up to three initial conditions and five independent coefficients on the system of equations being modeled. Output information is provided via the panel voltmeter or an oscilloscope (in our case, a modern Tektronix 3014 Data Acquisition unit). The photographs show the unit in a simple feedback test configuration transferring the output of one op-amp into the next.
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One example problem we recently performed for an educational demonstration was to simply have the computer multiply two numbers together. To do this we created a so-called 'broken key calculator' which would only calculate the value of six (the broken key) times any other value.
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Why? Simple, we had a 6 volt lantern battery hanging around the lab which would provide the number 'six' times any input we wanted to adjust on the computer. We could have used any battery type, or a variable power supply for that matter, but it just did not have the charm or simplicity of our one-sided calculator. The photo shown here contains the completed program where we are feeding the 6V input into the third coefficient bank via the seventh operational amplifier (the choice is arbitrary, we chose these two to physically separate the electrical connections making them easier to see in the photographs). The fifth coefficient potentiometer is acting as a reset button on a calculator (allowing us to zero out the result at any voltage level). |
The 'Broken Key' Calculator |
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The answer is then sent via the remaining red wire to the volt meter display on the computer. The ground of the meter was wired back to the negative terminal of the battery completing the electrical connection. The results of the calculation of 6 x (-1.5) = -9 is shown in the slideshow above. |
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