Difference between revisions of "CGS analog logic voltage processor"

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(Created page with "centre|400px'''CGS26''' the '''Analog Logic voltage processor''' module is the analog implementation of some basic logic elements. Instea...")
 
[[File:cgs photo cgs26 analogic.jpg|centre|400px]]
[[File:cgs photo cgs26 analogic.jpg|centre|400px]]'''CGS26''' the '''Analog Logic voltage processor''' module is the analog implementation of some basic logic elements. Instead of dealing with binary inputs, the "logic" is applied to whatever voltages are present on the inputs. When the AND element is fed several voltages, the output will equal the the lowest input voltage. The NAND output will be the inversion around 0 volts of the AND output. When the OR element is fed several voltages, the output will equal the the highest input voltage. The NOR output will be the inversion around 0 volts of the OR output. Apparently the AND and OR functions are the same thing as "peak" and "trough" on old Serge synthesizers, though they are implemented somewhat differently.
 
== How to use this module ==
 
== A little on how it works ==
[[File:cgs schem cgs26 v12 analog logic.gif|centre|840px|thumb|The schematic of the Analog Logic. There are minor differences between this diagram and the earlier version, notably with the output buffers.]][[File:cgs schem cgs26 v12 analog mixer.gif|centre|662px|thumb|The schematic of the onboard mixer included on the v1.2 PCB.]]The elements along the left side of the schematic are essentially "perfect diodes", that is diodes with a voltage drop of 0 volts. For the OR/NOR module, the diodes are forward biased, while for the AND/NAND module they are reverse biased. Pull down resistors on the inputs of the OR/NOR module set any unused inputs to the lowest voltage possible, so that those inputs will not affect the output. Pull up resistors pull any unused inputs of the AND/NAND module to the highest possible voltage for the same reason.
[[File:cgs schem cgs26 v12 analog mixer.gif|centre|662px|thumb|The schematic of the onboard mixer included on the v1.2 PCB.]]
The elements along the left side of the schematic are essentially "perfect diodes", that is diodes with a voltage drop of 0 volts. For the OR/NOR module, the diodes are forward biased, while for the AND/NAND module they are reverse biased. Pull down resistors on the inputs of the OR/NOR module set any unused inputs to the lowest voltage possible, so that those inputs will not affect the output. Pull up resistors pull any unused inputs of the AND/NAND module to the highest possible voltage for the same reason.
 
In both modules (AND/NAND and OR/NOR), the next op amp is wired as a voltage follower, to buffer the voltage from the combined inputs. Following that are traditional unity gain inverting buffers, the first giving the inverted outputs and the second giving the non inverted outputs for their corresponding modules. There is a trimpot in series with each of the output buffers, allowing the modules to be precisely trimmed for 1/V per octave on at least one of the inputs.
 
== Construction ==
[[File:cgs pcb cgs26 analogic.gif|thumb|centre|450px|The component overlay. Connections can be determined from the circuit diagram.]][[File:cgs pcb cgs26 analog logic.gif|thumb|centre|600px|The component overlay for the v1.2 PCB. Click through for an enlarged, printable version. Print at 300dpi for a correct scale printout.]]Note that the v1.2 board has the following issues: OR and NOR outputs have their labels swapped with each other. AND and NAND outputs have their labels swapped with each other.
[[File:cgs pcb cgs26 analog logic.gif|thumb|centre|600px|The component overlay for the v1.2 PCB. Click through for an enlarged, printable version. Print at 300dpi for a correct scale printout.]]
Note that the v1.2 board has the following issues: OR and NOR outputs have their labels swapped with each other. AND and NAND outputs have their labels swapped with each other.
 
Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.
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