Yann Guidon / YGDESThe RES15 relay is nice but requires way too much current to operate, in particular in some circuits where low current is necessary : the DRAM sense circuit as well as the instruction sense circuit, because 16 bits multiply the coil current, that reaches a value that can't be reliable...
Another type of relay is required and @Artem Kashkanov suggested the RES55 : a reed-type relay with the typical fast operation and low operating current, though at a higher voltage.
I couldn't find a suitable lot of this reference on eBay but found 2 other things :
- RES-64A rated 9-11V : vintage, pretty bulky, only SPST but 2K ohm coil so it must be pretty sensitive
- 1A12 : miniature SIP chinese reed SPST relays, rated 12V, 1K ohm coil, very cheap
I just tested the 1A12 and I am impressed : the contact closes at about 5V (varies with the piece) and opens at about 3V, with a current under 2mA. With such a hysteresis and low power, it even becomes interesting to use them for the register set...
I still have to receive the RES-64A, which would look way better, and I'll have to compare it to the modern miniature version. However there is now a good solution to the problem I had before : I can switch 16 bits on, and draw at most 2×16=32mA, which will not strain the address decoder's contacts much.
Oh and I still have to design that automated relay tester...
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And reed relays are pretty faster than usual one,. so It can be very helpful for DRAM refresh logic.
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yes however they can handle/switch less current and most often are SPST. So I use them as "amplifiers" for now.
If I start to want to replace all the RES15 I'll need DPDT reed relays and they use a higher voltage so it would also change all the power supplies and topologies...
DRAM refresh logic will be quite simple, I think. With a sensitive current sensor, the capacitor can retain data longer and refresh slower, reducing the wear of all the contacts.
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