Electronics > Projects, Designs, and Technical Stuff
Home Brew Analog Computer System
c4757p:
--- Quote from: IanB on February 10, 2014, 01:18:13 am ---However, I think in practice an automatic gain control circuit is required to keep the amplitude constant, otherwise any small errors in the system will be integrated without limit.
--- End quote ---
The beauty, though, is that it's only allowed to "oscillate" for one cycle.
GK:
Yes, a single cycle before initial conditions are reinstated; but see my subsequent comments on damping.
If an amplitude servo is added to facilitate continuous oscillation, you'll wind up with what is known as a State Variable Oscillator, such as this:
http://www.users.on.net/~glenk/thd/generator.pdf
GK:
I finally have a completed sin/cos, triggered timebase up and running using the above described method. Has 12 calibrated sweep speeds in 4 ranges, from 0.5s to 100uS in 1/2/5 steps. Other features included are an auto-triggering mode and user-variable trigger hold-off. I'm still tweaking a few component values and finalizing the schematic.
GK:
Things have been a little hectic for me lately, but this evening I finally managed to get the (almost complete) Fourier synthesis character generator/display unit up and running.
Here are the four main boards wired up:
Here is a closeup of the actual analog Fourier ROM for the 16 character character set (0-through-f). The IC's are all TL074 quad op-amps. The ROM is just a resistor matrix, the Fourier components simply being passively summed to produce the necessary X and Y deflection waveforms to trace out each unique character onto the CRT. Soldering in all of those resistors was about two or three orders of magnitude less tedious than actually computing the values.
When initially powered a random garble of characters appears on screen, depending on how the un-programmed screen RAM comes up:
For initial testing purposes, I wired a series for switches to the 12-bit parallel programming port, to manually program the display. The seven switches to the left are the address lines, selecting the actual character to be programmed, while the 5 remaining switches are the data lines. There are 17 characters if the blank space is counted. This is why I required 5 bits for the data port rather than 4. The (micro) push button to the far right is the strobe line. When pressed the address and data line status is written to the internal latches and seamlessly transferred to the screen RAM during the next subsequent blanking interval, updating the display.
Here is the display I initial generated playing with the switches. I numbered the columns (16) and rows ( 8 ) and left some of the random stuff in the middle.
dr_dan:
Beautiful! :clap:
Been waiting for this, since you posted a screenshot of "3" some while back!
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