The basics:
-Two oscillators
-Light controlled
-Two settings; LFO control and straight light control.
-LFO has rise and fall time control
-Pulse width control.
Laser sounds ensue.
More details:
This device is made of junk, recycled parts and wood and metal from sweet tins
Two LDR's (light dependant resistors) are used to make two voltage dividers which provide control voltages which are fed into two simple VCO's. The LDR's can be switched between +V and the LFO. The LFO is the charge and discharge of a cap in a standard CMOS schmitt oscillator, thus the peak to peak of the wave is only about 1V and it is biased up a bit. An op amp is used to remove this bias and amplify the wave to 0V to +V peak to peak voltage.
The charge and discharge periods of the LFO can be changed independantly, this allows you to make a saw or ramp shaped LFO waves for great laser sounds as well as a triangle LFO for siren sounds and anything inbetween!
I almost forgot: The 100k resistors in the mixing stage can be anything near 100k, I used 180k and 120k because I had no 100ks left.
I will post some sounds soon.
P.S. I also forgot to say, that if you use a different power supply voltage you will need to tweak the resistor values of the pulse width resistors/potentiometer and the non-inverting op amp stage.
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_________________ As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"
You are making a lot of nice instruments - i't fun to see what you're up to. Also, this drawing is very nice! _________________ http://soundcloud.com/douglasmseidel
Joined: Nov 10, 2011 Posts: 878 Location: Lancashire, England
Audio files: 14
Posted: Fri Mar 09, 2012 8:18 am Post subject:
Thanks chaps I cannot begin to explain how much fun this thing is to play! I'd really like to make another one and add a filter and envelope with a "trigger" button, maybe multiple LFO's too. _________________ As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"
Joined: Feb 19, 2011 Posts: 73 Location: Newcastle Upon Tyne
Audio files: 4
Posted: Fri Mar 09, 2012 4:36 pm Post subject:
nicely done man.
i like it.
I'm trying to get my head around the LFO non inverting op amp section.
I know you've got a scope. (i've seen a couple of your vids) It must help seeing the wave forms for finalizing values and what not.
Great idea by the way.
Also on a off note, where did you obtain a 4089 chip. (I'm in the uk too) I can't find one anywhere. Really want to try that chip out.
Joined: Nov 10, 2011 Posts: 878 Location: Lancashire, England
Audio files: 14
Posted: Sat Mar 10, 2012 12:35 am Post subject:
mrmrshoes wrote:
Also on a off note, where did you obtain a 4089 chip. (I'm in the uk too) I can't find one anywhere. Really want to try that chip out.
An old electronics shop called Progressive Radio Electronics; these 4089's could be over 15 years old!
I suggest you look for any privately owned electronics shops which have been going scince the 70's There are acctually two in my area, but I had to do a reasonable amount of googling to find them both. Get searching!
Now regarding the op amp stage, you mean the one after the LFO? That one is to remove the DC offset of the charge/discharge wave of the capacitor and amplify it to the maximum the op amp can, without chopping the top off!
In order to find the offset of the wave I think I used a voltage crossing detector (a simple op amp comparator like the two used for PWM in this circuit) adjusting the crossing voltage with a pot untill the wave at the output of the crossing detector was a tiny thin pulse (scope used for that) then checking the voltage at the pot with a voltmeter tells you the offset
I did it that way because my scope is a bit crap, the different ranges are not calibrated properly and can be off by 2 volts sometimes, so it's only really good for seeing waveshapes.
mrmrshoes wrote:
keep up the good work man
Thankyou I will!
This device goes on exhibition temporarily at the Liverpool World Museum today _________________ As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"
Joined: Dec 26, 2006 Posts: 144 Location: United Kingdom
Posted: Tue Mar 13, 2012 7:03 am Post subject:
Old times! I used to shop at PRS when I was a student in the 70's. I remember buying lots of exotic Plessey Telecoms scrap, including 'Trimphone' ringer PCB's and strange discrete - transistor auto diallers.
Like fool I left a superb 5V +/-15V supply I bought from them behind when I moved house. Just before seriously getting back into synth building.
Did you also go to Bert Ault's at Birkenhead? Now he did have some radical scrap. I bought a computer front panel covered in neon indicators, and still have a few other bits. I never could afford one of the inertial platform I saw there.
Joined: Nov 10, 2011 Posts: 878 Location: Lancashire, England
Audio files: 14
Posted: Tue Mar 13, 2012 7:55 am Post subject:
Fantastic
I have never been to Bert Ault's I will look him up _________________ As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"
Joined: Dec 26, 2006 Posts: 144 Location: United Kingdom
Posted: Tue Mar 13, 2012 8:43 am Post subject:
Sorry, my bad, I think Bert retired a long time ago.
I remember lugging home a huge linear 5Volt supply for my Sort of Polysynth/expanded organ, that was largely built from TTL logic. It must have weighed about 20lbs. I think it cost a whole £4 in those days a small fortune to a young would be student. Walked and took the bus. as I recall. I think Bert knocked the price down then I would have the fare home.
Don't seem to have many places like that these days, though I think Anchor Surplus are still trading.
I love the Lazer sound machine, by the way. I might dig out some perfboard over the weekend. Thanks _________________ Mike
Joined: Nov 10, 2011 Posts: 878 Location: Lancashire, England
Audio files: 14
Posted: Tue Mar 13, 2012 11:55 am Post subject:
Where about is Anchor surplus then? I want to visit all the remaining electronics shops!
Thanks for the compliments on my device
One could make a VC-LFO to control the VCO, using the VCO circuit but with a big cap, controlled by the LFO already provided it would make for some very interesting sounds
All I wish I had done with this device is add an arrangement like this for switching the LFO cap:
Code:
|
|
o
/
o o
| |
=== ===
| |
------|
|
___
-
'
The caps would be two very different values for two different ranges.
Even without this I am totally happy with this device I can even play tunes on it; with alot of practice and precision hand movements.
I'll get some photos soon because I plan to sell this contraption. _________________ As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"
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I cannot begin to explain how much fun this thing is to play! I'd really like to make another one and add a filter and envelope with a "trigger" button, maybe multiple LFO's too.
