Rebuilding my old analog console

[Kevint]

Laserist, Greg and Lasermaster1977: this is exactly they type of guidelines I need and it is really helping me develop my electronic skills. Thank you so much.

Here is the 555 timer results. I adjusted the period and frequency to 80msec/12.5hz, and it looks like the pulses are positive. See scope image.

I am extremely tired tonight and this is about all I can manage. Tomorrow night we have the grandkids. So, I will resume the investigation Thursday night.

Thanks again for the guidance,

Greg, I do like spaghetti but can get a bad case of OCD from time to time - lol

[sean1990]

Hello everyone

My name is Kevin. Back in the early 80's an old friend of mine was an electronic wiz and built a pretty elaborate analog laser light show console (some of you may even know him). He shared some of his schematics with me and I built a scaled-down simple version of it. That was 35+ years ago. I decided to take the parts that I had and rebuild the system. In a nut shell it consists of 4ea Burr Brown 4423 quadrature oscillators with a 3 position selector switch for selecting 3 different frequency ranges based on the value of 3 capacitors and a potentiometer to change the frequency range. The sine and cosine outputs go through a potentiometer to control the gain and then feed a switch matrix that connects to the summing amp. The switch matrix take each sine and cosine signal and feeds each of the 4 LM741 summing amps. This is how all the signal mixing was done. From there each of the 4 signals go into a power amp section. This consists of another LM741 op amp and a TIP41 and TIP42 transistor. There are 4 power amps to drive each of the 4 g120 x-y galvos (2 pairs). Sorry for the long description thats just how my brain works. I have the 4 oscillators, 2 summing amps and 2 power amps sections breadboared and working (for the most part). It drawing pretty nice patterns.

I am by no means an electronics person. I can tinker and get thing to work but not much more then that.

I would really like to add on some additional capabilities/controls like image rotation and such. In my friends system he had 4 VCAs after the summing amp and then some type of image rotation that used 4ea of XR2206 or XR2208 chips (I can't remember which chip it was - I'm getting old). Forgot - I also have a +/-15vdc offset signal feeding the op amps. Its uses a joystick the moves the image around

I'm doing this for fun and to share with my grandkids. If there is anyone here that can point in a direction for a schematic for VCAs or Image rotation that would be awesome. I would love to be able to add this functionality.

Thank you,

It's amazing to hear about your journey with building and rebuilding your laser light show console! Your dedication to recreating and improving upon the system after all these years is truly impressive.
Given your interest in adding additional capabilities like image rotation to your setup, I would recommend considering the Monport laser. It's renowned for its ease of use, high quality, and affordability, making it an excellent choice for enhancing your laser system. You can check out the Monport laser product on their website (https://monportlaser.com/?sca_ref=5031521.ka374VZjm3) to see if it offers the features and functionality you're looking for.
As for finding schematics for VCAs (Voltage-Controlled Amplifiers) or image rotation, you might want to explore online resources, forums, or communities dedicated to DIY electronics projects. Websites like GitHub, Instructables, or electronics forums such as Stack Exchange's Electrical Engineering community could be valuable sources for finding or discussing schematics with fellow enthusiasts. Additionally, searching for specific terms like "DIY laser light show schematics" or "laser image rotation circuits" might yield helpful results.
Good luck with your project, and I hope you continue to enjoy your journey into the world of electronics and laser technology with your grandkids!

[Kevint]

SUCCESS!!!

You are not going to believe what the issue was.

Lasermaster1977 your advice was priceless.

I took each part of the circuit and checked for appropriate output signals following your advice. I saw that the JFETs were triggering properly, I was seeing trigger signals through the op amps but no oscillations. I thought it might be sensitive to the types of caps like the 4423s are but that did not work. But it seemed that something was preventing the oscillations from occurring. While probing around on the breadboard, I notice that some connections were very intermittent and sensitive, So, I grabbed a new breadboard and transferred all the components exactly as they were on the that board - and success! The issue was a faulty breadboard. Not all the connections on the breadboard were making contact. This board was one of those cheap ones from Amazon. In this case buying cheap did not work out.

Here are some images. One without the symmetry pot and clipper amps and the other with them. Also the scope traces of the outputs.

Question: would using the pulse signal from the 555 timer output work as a blanking signal for the retrace?

[absolom7691]

Question: would using the pulse signal from the 555 timer output work as a blanking signal for the retrace?

I understand the want for a nice and clean spiral but I actually like the retrace lines!

[Kevint]

Thanks Steve I'll have a better reply is a few days. Just had my first experience with vertigo - so my head is not there yet. Got some meds from the doctor.

I totally agree, I also prefer the retrace line. It adds that natural analog feel to the image which I really enjoy. The main purpose for asking the question is to try to understand where these blanking signals come from and in this case could the 555 time pulse be that source. But all in all, both of us are on the same page. Thanks for your comment.

[lasermaster1977]

SUCCESS!!!

You are not going to believe what the issue was.

Lasermaster1977 your advice was priceless.

I took each part of the circuit and checked for appropriate output signals following your advice. I saw that the JFETs were triggering properly, I was seeing trigger signals through the op amps but no oscillations. I thought it might be sensitive to the types of caps like the 4423s are but that did not work. But it seemed that something was preventing the oscillations from occurring. While probing around on the breadboard, I notice that some connections were very intermittent and sensitive, So, I grabbed a new breadboard and transferred all the components exactly as they were on the that board - and success! The issue was a faulty breadboard. Not all the connections on the breadboard were making contact. This board was one of those cheap ones from Amazon. In this case buying cheap did not work out.

Here are some images. One without the symmetry pot and clipper amps and the other with them. Also the scope traces of the outputs.

Question: would using the pulse signal from the 555 timer output work as a blanking signal for the retrace?

Congrats Kevint! Nice image results, too. Many times it is just the simple things.

You couldn't use the 555's output directly as a blanking signal since it is 0-15v. Some some down scaling and buffering would be needed to get down to a 0-5v signal. But, I don't recall what you are using for laser LED intensity control.

It would interesting to do this circuitry with one TL084 for the KQO 3 op amps and the Clipper op amp.

[Kevint]

Thanks Lasermaster1977. I'm reliving some of the same joys that Greg has.

Currently not using any laser diodes at the moment. Just using some old HeNe's and a DPSS laser I had laying around. I was just going to use a scanner to test blanking. I'll see if I can put together a circuit that sends the 555 signal to a blanking scanner and see what happens. Any recommendations on what would be a good RGB laser to get? One with good beam quality for image/graphics?

I agree, trying to use TL084 could really reduce the complexity and footprint. I'll include some on my next electronics purchase.

[lasermaster1977]

Thanks Lasermaster1977. I'm reliving some of the same joys that Greg has.

Currently not using any laser diodes at the moment. Just using some old HeNe's and a DPSS laser I had laying around. I was just going to use a scanner to test blanking. I'll see if I can put together a circuit that sends the 555 signal to a blanking scanner and see what happens. Any recommendations on what would be a good RGB laser to get? One with good beam quality for image/graphics?

I agree, trying to use TL084 could really reduce the complexity and footprint. I'll include some on my next electronics purchase.

To use the 555 output to feed a blanking drive circuit I would recommend a method that would lightly load its pin 3, i.e. a digital buffer. Another 555 could be used for this buffer and its output would then feed whatever scan driver circuit you have. I should add that a CMOS inverting buffer should be placed put between the 555 output and the 2nd 555 used as a Schmitt Trigger.

Using the 555 output for blanking would also depend on the "flag" method you are using on the scanner shaft to effect occluding the beam ON and OFF and how much angular deflection is required for the "flag".

One nice thing about the 555/556 timer chip is that it can sink or source up to 150-180 mA of current.

Here is an example of a dual 556 Schmitt Trigger w/dual "AND" inputs. This implementation uses standard TTL signal voltages. There is a signal inversion between Zin's and Zout's so an inverter buffer is required on the Zin inputs (the inverter needs to be before the ZinRGB inputs for the circuit to work as intended). So not shown in this schematic are TTL inverting buffers feeding those RGB inputs. In addition, there are optional non-inverting TTL level "Computer Zin" inputs signals on the Reset pins. Any blanking signal on these pins are logically AND'ed with the other Zin inputs. I used a variable square wave oscillator as inputs to the Zin-RGBs for adding blanking ON/OFF signals to computer generated image blanking signals feed to the Computer Zin's. This was before I had any analog 0-5v intensity signals and only TTL based blanking signals. I'm pretty sure I described all this correctly...old age adds in unexpected memory quirks. I last built the related PCBs back in 2019.

[Kevint]

Thanks Lasermaster1977. This is really great info. I need to think about all it and put a plan together. At the moment I have zero blanking setup so I will need to put it all together - scanner, mount, flag, scan amp... this will take a couple weeks and then revisit this topic.

Just not enough time in the day. I'm retiring in a year and a half. I can't wait.

[Kevint]

Lasermaster1977: you and me both. I play lead guitar on our worship team and a song I learned a few weeks ago will be lost from my memory the next time I play it. Getting old has it's moments.