I like all sorts of electronics, analog and digital. I can't really understand why most computer types are really scared of touching hardware. Recently I have not had the time to hack much on electronics, except for 6.111 (digital design lab hell). For my final project in the class, I designed and built a digital vector graphics engine.

I have a number of HeNe lasers and a pile of mirrors that I have yet to do anything interesting with. Right now I'm still looking for scanning galvos and AO modulators with which to build a decent graphics rig.

sgw just dumped some nifty stuff on me, including some LN01 guts and some autotransformer based dimmers. Maybe I'll get the AO modulators working. Yeah right.

970609:

Heh. Got the AO modulators working. Unfortunately they're of the digital variety, and only deflect the beam at a fixed angle. I don't feel psyched to build a ~100MHz VCO just yet... Picked up a couple of General Scanning G330 galvos at a swapfest, and hopefully I'll get an amp built for them. I may also be building scary things like variable quadrature oscillators in order to make analog cycloid generators and rotators with which to drive these things. You see, Analog Devices has this wonderful analog "trig function" chip that would be just right for this kind of thing. I'm also looking at getting some G325 galvos when I scrape together the money. I'd love to hear from anyone who has functional G120s for cheap...

971124:

Picked up a couple of G325 galvos. Still havent' gotten them to work yet, as I'm still trying to build a workable servo amp. Meanwhile, real work and random theatre type things have intruded into the electronics hacking. Somewhere along the line I also got an ADM-40 modulator, though I still don't have the specs or a driver.

980707:

So it turns out I was really really confused about how AO modulators work. The modulation, at least for a standard single-wavelength Bragg cell configuration, is basically keeping the beam at a fixed deflection angle by using a fixed RF input frequency to the acoustic transducers. By varying the RF power, it is possible to vary the diffraction efficiency of the "grating" that is produced in the crystal, and thus, the amount of optical power that ends up in the first order diffracted beam. I'll elaborate on this later when I have time to properly write up what I've learned about the wonders of acousto-optics.

Let's just say that after some amount of frobbing, I actually did get the ADM-40 to work, after a fashion. Its center frequency is about 40MHz, which I don't have any test gear capable of generating just yet. As a result, I drove it with my Yaesu FT-50R transceiver, which showed that it actually did work, though the diffraction efficiency was way down, probably due to the >100MHz signal being attenuated greatly by the transducer dynamics as well as by the loading coil that was feeding the transducers. I estimate, just by visual inspection, that the first order spot was probably less than 10% brightness. At some point I'll build what is effectively an AM transmitter centered on 40MHz to drive it. I just have to make the input signal be DC-coupled all the way to the AM modulator.


back to Tom's homepage
updated on 980707 / tlyu@mit.edu