# Sense "Amplifier" Circuit...

A project log for Incandescent RAM

Use lightbulbs to store data!

Eric Hertz 09/26/2023 at 13:515 Comments

Ken Shirriff did a writeup on DRAM...

check this baby out... looks a heck of a lot like what I came up with!

In my case I'm essentially measuring a small *resistance* difference, rather than voltage. But, of course, the voltage-divider created by those resistances is what's responsible for which relay "wins." The 50 ohm (calibratable) resistor is essentially our reference resistance. If the bulb resistance is higher than 50 ohms, it's considered "on" and the lower relay turns on faster than the upper relay, cuting it out of the circuit. (The bulbs measure roughly 10ohms cold, 100 hot).

[The 10ohm resistor is an addition for the refresh circuit to self-reset when it advances from one bulb to the next.]

Simulations, long ago, showed that a bulb could be determined as having been "on" when its resistance had dropped *dramatically*. Real-world tests were not expected to go as well, yet really did far better than I expected, "bits" retaining their value for upwards of a second [of course, that also means that *clearing* a bit to zero also takes upwards of a second], while only being refreshed for a fraction of that. This, too, was a bit of a surprise; I kinda figured I might have to use higher voltages than the bulb's rating to get it to heat fast enough. But, instead, I was able to get a functional system running at less than the bulbs' rated voltages. Increasing the voltage, then, might allow for longer durations between shorter refreshes, which would mean more bits could be handled by the same sense/refresh circuit. [This "sense" circuit also "refreshes" the bulb.]

## Discussions

Dr. Cockroach wrote 09/27/2023 at 16:12 point

Still, at least you are picking up. I have been dragging my heals on my projects for way too long and need to get a fresh start. Also started working part time to help pay the bills :-(

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Eric Hertz wrote 09/27/2023 at 20:30 point

I heard you'd been doing that... That can surely put a damper on project-energy and time... As far as 'mad scientists' go, I've seen you amongst the most-imaginative and productive. And accessible/educational, to boot. Down-time on projects (ala writer's block) is hard enough to fight through... The economy has done the world a disservice in further impeding progress on whatever projects you put your mind to!

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Dr. Cockroach wrote 09/28/2023 at 00:07 point

Thanks for the kind words. Yeah, writers block does best describe my time right now. The good thing is that I am working at a seniors thrift store receiving donations and checking out what works and what does not. Some interesting electronics come in the back so I might have a golden op to snag some interesting future projects :-)

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Dr. Cockroach wrote 09/27/2023 at 11:12 point

Darn, you are making some good advances in this :-)

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Eric Hertz wrote 09/27/2023 at 12:48 point

Oh, thanks! but, actually, I was just remembering where I left-off a yearish ago... heh!

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