The Dynatronics Model 820 was one such device. Dynatronics was and still is a manufacturer of a variety of medical therapy products. I haven't really spent much time on their Web site so I can't comment on whether what they sell now is useful. The model 820 almost certainly was not, at least not more than as a placebo. However, to their credit, it is much higher quality than I had originally expected, which would have been a cheezy surplus barcode scanner tube duct-taped in place with a discrete linear power supply cobbled together from junk parts. But this is not the case.
The parts are first rate and the general construction technique is really quite good with fiberglass-Epoxy PCBs and most wiring using cables with AMP connectors and. It uses a genuine Hughes model 3222H-C laser head which has a hard-sealed modern tube, random polarized and rated 2 mW. It has a sticker stating 2.75 mW when new. Its power output currently measures over 2 mW at power-on through the plastic chopper wheel (more below) so it may indeed approach 2.75 mW after warmup. The power supply is a Laser Drive 115 VAC input brick. I have no reason to suspect that they bought anything other than new lasers since there was no eBay back then, though I suppose some of the laser surplus places did exist in 1981 (the date of manufacture of this unit). However, the laser head and power supply are dated 1980, so seeing them surplus in 1981 would be unusual.
The output of the laser feeds an optical fiber or light guide which goes to the "probe", after passing through a plastic motor-driven chopper wheel. I doubt there is any focusing as the coupling efficiency is terrible - no more than 25 percent makes it to the probe tip. I don't think anything is misaligned, but being that way, it among other things, stays within the less than 1 mW of a Class II laser. The end of the probe cable at the laser is made of metal and passes through a pair of opto-interrupters which act as a safety interlock: The laser will not turn on if the probe is missing, nor can the probe be removed if the laser is on as there is a solenoid that latches on the metal section. AC power must be on but the laser must be off to remove the probe cable. There is also a standard 2 pin Jones plug electrical interlock which must be present for the laser to turn on.
The "controller" consists of a pair of PCBs. What I'm calling the "Main PCB" has the DC power supplies and circuitry to enable the laser and chopper wheel motor and control its speed, and for the timer that sets the duration of laser exposure in timed mode.
While I complement Dynatronics on their construction quality, they also appear to have the paranoid mentality of a fly-by-night operation. Specifically, the part numbers on most ICs and transistors have been sanded off! For the most part, this would not impede reverse engineering by anyone with a competence level above that of a carrot, so it seems silly. And it would be even easier to simply duplicate the functionality. This isn't rocket science! And the Main PCB seems somewhat more complex than necessary to implement the required functionality, so I wonder if all the parts actually do something. :)
The display on the front panel and the audio have nothing whatsoever to do with the laser or its output and are active as long as power is on. Both are based on the resistance between the probe tip and the cylindrical aluminum electrode or rod which one is presumably supposed to hold onto while digging the probe into whatever body part is to be irradiated. Then, the display shows a number from 0 to 100 to indicate how good the conductance is with 0 being infinite resistance and 100 be 0 ohms with 100K coming at 50. The display runs off a 7107 A/D IC (common back then for any sort of application requiring a 7 segment digital readout of an analog voltage). The audio output is from a Sonalert beeper gated by a 555 timer whose repetition rate depends on the conductance. So, it's an increasing warble of sorts. The control on the front panel only sets loudness over a modest range, which unfortunately doesn't include mute. :( :)
The laser may be turned on either directly by a pushbutton on the probe, or that may latch a timer with a duration of from around 5 to 30 seconds based on the setting of the front panel pot. Whenever the laser is on, a motor rotates a chopper wheel in the beam to produce a variable rate modulation of the laser output. The motor speed is controlled by another pot on the front panel.
I'd love to locate a copy of the instruction manual that went with this thing, especially the part about how to cure various dreaded afflictions. ;-)
The value shown in the 2-1/8 digit display (up to 100) is based on the resistance between the probe tip and the hand-held cylindrical electrode that plugs into a banana plug next to the main probe on the left connector. A 100K resistor to a DC voltage feeds the probe tip while the hand-held electrode is effectively another 100K ohm resistor to ground, forming a voltage divider. The displayed value is then calibrated via the trim-pot on the front panel PCB to be 100 when there is no additional resistance between them. Unfortunately, the voltage regulation isn't so great, so when the motor turns on, it may drop by 1 count. Darn. :)
The 555 provides a variable rate enable to the Sonalert based on the (analog) value in the display so it kind or warbles at an increasing rate for higher values. The Audio Level front panel control is simply in series with the Sonalert and provides a modest range of volume.
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