Electronics > Projects, Designs, and Technical Stuff
Home Brew Analog Computer System
timofonic:
Would a similar design using SMD be possible and provide some advantages or the high current would do it unable to be made?
rstofer:
--- Quote from: timofonic on April 02, 2016, 08:02:12 am ---Would a similar design using SMD be possible and provide some advantages or the high current would do it unable to be made?
--- End quote ---
The OP is building a 100V Analog Computer. SMD parts may be hard to find.
Later generations used 10V as '1' so, yes, SMD parts definitely apply. I used socketed 8 pin DIPs so that I could try various op amps (which I never have) but my next version will likely use SMD. I just need to settle on some particular op amp.
Accurate capacitors will be a problem regardless of form factor and the capacitor is the key ingredient for the integrators. There used to be some very accurate capacitors used in commercial analog computers. I have yet to find a source much less in SMD. 0.1% would be acceptable.
Here is the machine I built. It has 2 integrators, 3 summers and an inverter plus some other gadgets like a multiplier. Two integrators is a serious limitation except that it will handle many problems in mechanics as it can handle acceleration, velocity and distance as this only requires two integrators.
http://www.analogmuseum.org/english/homebrew/vogel/
GK:
--- Quote from: timofonic on April 02, 2016, 08:02:12 am ---Would a similar design using SMD be possible and provide some advantages or the high current would do it unable to be made?
--- End quote ---
Since an analog computer is an antiquated thing I decided to stick with traditional through-hole parts (mostly) throughout, though if you are only referring to the shown deflection drivers for the display unit, they could be mostly implemented in SMD except for the power output devices, which is more practical in through-hole due to the power dissipated. For example the originally vertical (now horizontal as the display is rotated 90 degrees) deflection channel with the re-wound yoke coil requires just shy of +/- 2A peak for full scale deflection (to deflect the dot from the center of the screen to either edge). The supply rails are +/-40V, so if the dot is (horizontally) static at the edge of the screen the deflection amplifier is dissipating ~80W.
GK:
Here is the current supply arrangement to provide all of the operating potentials required of the CRT while I continue to prototype and test the (again) re-designed/improved deflection amplifiers.
I hack-sawed the direct off-line part of the PSU from the donor televisions motherboard and rebuilt the LOPT section dead-bug style on a rectangle of blank PCB, minus all of the superfluous functions.
The direct off-line part is a bit of a crappy discrete self-oscillating fly-back with voltage mode control - I have actually traced out the circuit in its entirety. A BU508 power transistor does the primary switching and a auxiliary secondary winding is used exclusively for feedback and regulation. The secondary winding for the supply rail outputs has a single tap to provide two supply rails (half-wave rectified) of 18V and 110V. The associated rectifier and filter caps are now located on the new LOPT board.
I'll design my own substitute off-line regulator utilizing the magnetics, but I'll do away with the crappy BU508 and all those high power resistors associated with the base-drive circuitry.
The 110V rail, originally serving both the deflection an LOPT circuitry, now only serves the LOPT. The 18V rail now powers an LM555 timer (via a 3V zener V-dropping diode) which substitutes for the horizontal timebase. The TVs original circuit used a 2SD1398 "flyback driver" transistor (with integral anti-parallel diode) BJT to switch the primary current of the LOPT, itself driven from a base-drive coupling transformer and open collector switching/driver transistor receiving the 15.626kHz, ~50% duty cycle horizontal signal from an LSI "horizontal/vertical combination" integrated circuit. I substituted all of that with the LM555 directly driving an STW4N150 MOSFET.
These LOPTs operate in a resonate mode with an external parallel capacitor (which I simply pulled off the TV motherboard). When operating correctly the primary voltage waveform is a clean high-voltage half-sinewave, as shown in that attached scope screenshot (alongside the MOSFET gate-drive waveform). The LOPT provides the final anode, focus grid, screen grid and heater supply voltages for the CRT.
GK:
Long time no post. Got this little projects 19" frame assembled this evening. Now I have 84U to fill.......
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