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Adventures in Simulations and Thought

A project log for Homemade DRAM-like thing from TTL logic gates

I like to build circuits with 7400 series logic chips. DRAM-like is perfect because it's big, has plenty of logic, and has some challenge.

Dylan Brophy 4 days ago2 Comments

I have been thinking a lot about how I would get the relay DRAM to work as I want it, and how to save parts at the same time. I originally referenced YG's https://hackaday.io/project/18757-ygrec16-ygs-16bits-relay-electric-computer/log/49877-capacitors-and-diodes project log for an idea of how to make large amounts of DRAM. This design uses TONS of diodes and theoretically does not support non-volatile storage (discussed in previous log), although I haven't tested that.

I only have maybe 60 diodes. Some are in PCBs. So, I would have to order a few hundred diodes from @Digi-Key Electronics. I don't want to spend more money on parts other than maybe more capacitors, so I decided to run a simulation of the DRAM without diodes. It worked! and it's still non-volatile in it's weird capacitor-based way.

I don't have many relays (yet), that's why I didn't actually build the circuit. It does seem in the simulation however that the diodes make the memory work worse, not better. A real circuit will tell if I need the diodes.

I think the diodes were for preventing capacitor loops. Since I am using relays to 'disable/enable' the capacitors, the loops never occur. So in theory the diodes are unneeded.

You may view the simulation here.

Discussions

Yann Guidon / YGDES wrote 4 days ago point

Hmmmmm..... I'll have to check your assertions.

Particularly since I just received a reel of 10K+ dual diodes :-D

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Dylan Brophy wrote 4 days ago point

Oh.  I don't even know what to say...  Try the simulation and tell me what you think - Or actually build the circuit.  Tell me what you come up with.

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