360' Electromechanical Oscilloscope

project name " Tachyscope Laser "

This is how I built a 360' laser based electromechanical oscilloscope using a small stepper motor as a galvanometer, a 12" plastic plate as a turntable to mount the stepper/ mirror onto , HE NE laser tube as a light source, and 100 year old 4 pin vacuum tubes for the amplification of the audio source to drive the galvanometer.

I will be focusing on the Oscilloscope section of this project, not the cabinetry or keyboards.

Cautionary note: This project uses laser light, High voltages and motors rotating. Use appropriate safety precautions as needed.

item 1: circa 1970 Helium Neon laser tube. ( you can replace with LASER pointer)

item 2: small stepper motor used as a galvanometer

item 3: 12" serving tray as the turntable / mounting plate.

item 4: mirrors from old laser printer ( glued to stepper motor shaft), cut mirrors as small as possible, minimize its mass.

item 5: HV power supply for laser tube, not needed if using LASER pointer as light source.

item 6: circa 1920 Audio tubes, Im using UV-201A 100 year old tubes for the amplifier, any small audio amp will work.

item 7: a box to mount the project, in this case I built a wooden cabinet.

item 8: motor / belt and pulley drive. Speed controlled by PWM driver board.

item 9: drive shaft support. (axle), note must have hollow shaft to enable the Laser beam to travel up to mirror on galvanometer.

Laser beam leaves the laser tube does a 90' turn downwards, then 90' sideways into the center of the wooden cabinet, then directly in the center of the drive shaft tube another mirror sends the beam upwards to the final mirror mounted on the stepper. The beam is focused on a "target" screen attached on the rim of the plate.

The circuit to drive the stepper is relatively simple, all the coils of the stepper are wired in series / with a center tap. One leg of the stepper goes to +5v, the opposite leg to ground and finally the center tap gets the audio amp output.

Spinning the turntable in a CCW direction will generate the "horizontal" axis "X"

Stepper motor/ mirror will generate "amplitude" axis or "Y".

In this project I wanted to use the oldest possible vacuum tubes for amplification/ drive for the stepper- galvanometer.

Decided on the UV-201A common in battery radio sets from the 1920's. Even as they are 100 plus years old, some are weak, some where dead, was able to MacGyver a working circuit. I'm not a tube expert ( my 2nd project ), using some tubes I was able to come up with a viable circuit. I couldn't find a comparable schematic design so I made my own.

Some of you vacuum tube officiato out there might find issues with my design, your insight is welcomed. In short the circuit works.

I salvaged ( scavenged) parts for the amp from an old battery set and a more recent 1960 chassis. I got a bunch of old tubes in a box, mostly all where bad.

I wanted brass based 4 pin tubes, hard to find, so I repaired some by removing the brass base from a bad tube and replacing the defective tube with a tested working one. Success 4 working tubes.

Now developing the circuit

During the prototyping stage, I starting with 1 tube, then 2, found that I needed 4 tubes to be able to drive the galvanometer. -side note- in order to get the B+ voltage a quick and dirty trick is to stack up a whole bunch of 9v batteries. works great for testing.

I needed to get power and Audio up to the galvanometer, this is how I built a 4 pole slip ring.

Started with an old "C" cell battery, removed the insides ( carbon and electrolyte ).

Took a plastic pipe and slid the battery casing over it.

Cut 4 "rings" into the casing, giving me a 4 pole slip ring, soldered wires from inside the rings.

Next using a 4 pole relay to act as the contacts, removed the 4 pole "fingers" .

The drive motor salvaged from an old battery powered hand held vacuum cleaner.

Mounted it via drive belt and custom made pulley.

Next you can see the laser beam exiting the laser tube, doing a 90' downward change, then just below that another 90' horizontal change before entering the center of the cabinet ( see my hand with red dot).

link to Youtube of this project

https://www.youtube.com/watch?v=QZCZG0h7Kas

or

search by " Tachyscope Laser "

In this Instructable I only covered the Laser display, not any other sub assembly like the control panels, Dekatron tube, making the brass plates, wooden cabinet,, those to follow in a later project.

If you're looking for more details / info drop me a note here.

Cheers

Daniel