3 ms·

By the way there are cheap and easy to use quartz delay lines used in old TVs.

orbital-decay 3y ago
Those provide 64 microseconds delays, which is probably too short to store data for a slow machine like this. Delay lines used in storage typically provided single-digit ms.
- Animats 3y ago
  A few of those in series, with a regenerator stage after each one, would work. It's hard to find non-IC delay lines today. "Analog" delay lines in guitar pedals now use a charge-coupled bucket brigade IC. They're analog in amplitude, but discrete in time. I was expecting that someone would still be manufacturing some kind of acoustic delay line product, but there's not much out there. The EDSAC rebuild people built a delay line memory.[1] Not too complicated, but a pain to get it to work. You need a piezoelectric or magnetostrictive transducer driving a metal rod, with a receiving sensor at the other end. Liquid level sensors which work that way are common. A metal rod dips into the liquid, and a transducer at the top sends a ping down the rod. The impedance change where the rod enters the liquid causes a reflection, which is sensed by the transducer that sent the pulse. Converting one of those into a delay line might be possible. You need some length. The speed of sound in steel is around 5,000 meters per second, so you'll need 5 meters for a millisecond delay. This can be a coil; it doesn't have to be straight. A longer delay line can store more bits, but the cycle time is slower. These things are temperature sensitive, so they either have to be self-clocking or temperature controlled. [1] https://www.youtube.com/watch?v=9BA4AyvlKnM https://www.youtube.com/watch?v=9BA4AyvlKnM
  - orbital-decay 3y ago
    If I remember correctly some old textbooks I've read, these lines were usually made of invar or a similar alloy to avoid the thermal expansion, and the torsional wave spreads slower (around 3km/s). Reflections were dampened using rubber pads.

Those provide 64 microseconds delays, which is probably too short to store data for a slow machine like this. Delay lines used in storage typically provided single-digit ms.

Animats 3y ago
A few of those in series, with a regenerator stage after each one, would work. It's hard to find non-IC delay lines today. "Analog" delay lines in guitar pedals now use a charge-coupled bucket brigade IC. They're analog in amplitude, but discrete in time. I was expecting that someone would still be manufacturing some kind of acoustic delay line product, but there's not much out there. The EDSAC rebuild people built a delay line memory.[1] Not too complicated, but a pain to get it to work. You need a piezoelectric or magnetostrictive transducer driving a metal rod, with a receiving sensor at the other end. Liquid level sensors which work that way are common. A metal rod dips into the liquid, and a transducer at the top sends a ping down the rod. The impedance change where the rod enters the liquid causes a reflection, which is sensed by the transducer that sent the pulse. Converting one of those into a delay line might be possible. You need some length. The speed of sound in steel is around 5,000 meters per second, so you'll need 5 meters for a millisecond delay. This can be a coil; it doesn't have to be straight. A longer delay line can store more bits, but the cycle time is slower. These things are temperature sensitive, so they either have to be self-clocking or temperature controlled. [1] https://www.youtube.com/watch?v=9BA4AyvlKnM https://www.youtube.com/watch?v=9BA4AyvlKnM
- orbital-decay 3y ago
  If I remember correctly some old textbooks I've read, these lines were usually made of invar or a similar alloy to avoid the thermal expansion, and the torsional wave spreads slower (around 3km/s). Reflections were dampened using rubber pads.