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Home Brew Analog Computer System

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C:

you just need the electronic version of a  mechanical clutch.
On trigger you drop the clutch connecting the input (the X & Y signals) to the Output X & Y signals that was set to start with the desired starting reference..

I think Selsyn and Synchro Devices were some of the first IO devices of an Analog Computer
http://en.wikipedia.org/wiki/Synchro

Think of what a Sine wave really is, the result of having a marker attached to rim of a rolling circle when the rim is rolling on a line.
If you are thinking the circle has a shaft then rules have to change for that way of thinking.

I think I remember from a very short crash course on Selsyn's that there is a circuit that will do what you want. One of the first uses of a CRT was as an improvement from using Selsyns. So in the dust of time is probably the circuit with a good description.

Note that what you create for circuits today could be much more complicated due to not using something very common in old days.
A simple OP amp is shown as two variable resistors connecting the two supplies to a common output. In the old days it was not unusual to have resistors added to the supply leads of the output variable resistors.
By adding the two resistors, a single ended center input Op Amp could convert to a differential output from the power rails. Need more signal swing, connect the outputs of two Op Amps together with only one having the two to-rail resistors.

It was also not uncommon to have output of one or more Op Amps supplying the rail voltage to another Op Amp.

Some things you do not see much of these days

C

robrenz:

--- Quote from: C on January 31, 2014, 06:46:13 pm ---Think of what a Sine wave really is, the result of having a marker attached to rim of a rolling circle when the rim is rolling on a line.

C

--- End quote ---

That would be a Cycloid not a sine wave.
http://en.wikipedia.org/wiki/Cycloid

C:

--- Quote from: robrenz on January 31, 2014, 07:28:16 pm ---
--- Quote from: C on January 31, 2014, 06:46:13 pm ---Think of what a Sine wave really is, the result of having a marker attached to rim of a rolling circle when the rim is rolling on a line.

C

--- End quote ---

That would be a Cycloid not a sine wave.
http://en.wikipedia.org/wiki/Cycloid

--- End quote ---
Yes,
 forgot the connecting rod.
or the slide slot.

C

GK:

--- Quote from: C on January 31, 2014, 06:46:13 pm ---
you just need the electronic version of a  mechanical clutch.
On trigger you drop the clutch connecting the input (the X & Y signals) to the Output X & Y signals that was set to start with the desired starting reference..
--- End quote ---


I'm afraid it is not that simple. What you describe provides no mechanism for synchronizing the zero crossing of a free running sinusoidal timebase (oscillator) with the trigger pick-off threshold/point of a periodic input signal.

BTW, there is only one input signal (neither X nor Y) - that representing the distance from the pole, r.

Perhaps this simplified block diagram of the prototype circuit will make things clearer:



Polar coordinate system explained here:
http://en.wikipedia.org/wiki/Polar_coordinate_system



   

johnwa:

--- Quote from: GK on January 31, 2014, 11:39:23 pm ---
I'm afraid it is not that simple. What you describe provides no mechanism for synchronizing the zero crossing of a free running sinusoidal timebase (oscillator) with the trigger pick-off threshold/point of a periodic input signal.

BTW, there is only one input signal (neither X nor Y) - that representing the distance from the pole, r.

Perhaps this simplified block diagram of the prototype circuit will make things clearer:
 

--- End quote ---

Hi GK,

It is nice to see some more analogue computation ideas on the go! One of the things on my to-do list at the moment is a phasor display for working with polyphase systems. I am thinking that I will generate some quadrature sine waves, then multiply with the incoming signals and low pass filter to get the endpoints. A further multiplication with a ramp will give the lines for the phasors.

This is a somewhat similar situation to your current problem, though I was going to have my oscillator phase locked to one of the incoming signals, but otherwise free running.

One thought occurred to me - would it be possible to 'freeze' the state of a quadrature sinewave oscillator using some sort of sample and hold? It could then be set up to a known phase angle, then triggered by the input signal. I haven't really though through the details of this, but it might possibly be worth investigating.

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