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New DRAM array

A project log for YGREC16 - YG's 16bits Relay Electric Computer

Fork of #AMBAP, here I discuss about the physical implementation of the bitslice architecture with russian РЭС15 (see what I did here?)

Yann Guidon / YGDES 04/01/2017 at 20:312 Comments

I just had the best idea of the last days, in the most unlikely place, but I'm not surprised anymore because that's the way progress happens : with cross-polination of ideas :-)

So I was returning to the #Dot flippers page and looked at the schematic of the arrays... The log Wild guesses contains some useful ideas, such as this image :

Everything is there ! This is the solution ! Just replace the coils with capacitors ! Diodes to the rescue !!!

When the previous DRAM array circuit is rotated 90°, the circuit saves the large duplicated MUX that connects the diodes to 0V. After all, only one of them will conduct current.

The revised DRAM circuit is there :

The added diodes to the left increase the voltage drop but it's not significant. Their leakage though is critical.

The increase in diodes count is not significant but the saving in relays is great ! Less relays means less power consumption, fewer assembly hassles and less expensive...

So the number in the log Backplane routing considerations must be corrected.

512 words is in the realm of possible but I'll start with 256 so I need "scalability"!


Wait !

Wait wait wait !

There's something else with the flip dot arrays : all the lines are driven simultaneously and only one column is active ! Could this be applied to our capacitor array ? If it is possible (without the gotchas that I was pointed to in the first iteration of the DRAM array) then I can save AGAIN a whole lot of relays and use only one MUX for all the columns ! I must test this ! If this holds true then


Following @roelh's comment, here are the (expected) current flows through the MUX and array:

Discharge:

Charge:

I hope it's clearer now :-)


Re-update: falstad simulation shows @roelh's concerns were justified... See https://hackaday.io/project/20864-ygrec-15-bis/log/56753-first-dram-array-prototype#discussion-list

Discussions

esot.eric wrote 04/03/2017 at 01:10 point

Good luck! 

I still don't get the diodes... oh, so one capacitor doesn't discharge into the next?

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2017 at 01:14 point

Something like that... it's a bit more convoluted though but without them, the array won't work.

  Are you sure? yes | no