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Sonia Rinaldi ~ The Light Bridge version 4


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I recalculated the costs for the components today. My goal was to choose only one supplier for all parts I needed to cut down shipping costs. Thus I will slightly change the schematic accordingly but not in functional ways, because I will use another operational amplifier. The one I originally used is not on stock from the supplier I chose.

I also took into account the costs for components I omitted in my first calculation because I had them lying around in my shack. As long as I intended to make just one unit this was ok but now as it turns out that more people want this device I took them into the calculation.

So the "real" price for manufacturing the light bridge is 60€ with shipping costs coming on top. Lance, is this still OK for you? I would agree to keep the price at 50€ for you because that was my first calculation. However for every new device the costs will be 60€.

 

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This is the completed device. Upper housing not fully closed yet.

IMG_20210918_114538.thumb.jpg.b1f8d008005ebeada395860aee6d8300.jpg

The look to the inside. I extensively used hot glue to fix cables and solderpoints which are likely to break under mechanical strength.

IMG_20210918_114420.thumb.jpg.f27393a0e5c61febf97740943daae334.jpg

I used a rock crystal as a diffuser for the LED. I hope the spirits will appreciate this.

IMG_20210918_114428.thumb.jpg.a487e89d3f7f35be0b13daf33abac12d.jpg

Now I must look for a power supply. I have dozens of them, so that's no issue I guess. I even remember I have a UK adapter in my attic somewhere.

I also will put some labels at the front face yo facilitate the use of sockets and potentiometers.

Lance, I will make a small video to show you howto operate the device.

 

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Andres, what a great piece of engineering. Well done. I liked the use of the rock crystal as a diffuser. I was going to ask you about that, and what the signal to noise ratio is from the solar cell, as it needs to be a bit poor.

It will be exciting to see Lance using it.

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15 minutes ago, Dr Jeffers said:

Andres, what a great piece of engineering. Well done. I liked the use of the rock crystal as a diffuser. I was going to ask you about that, and what the signal to noise ratio is from the solar cell, as it needs to be a bit poor.

It will be exciting to see Lance using it.

Yes Im curious too! I just tested the device technically. Making spirits speak through it I leave up to Lance. The signal contains a nice share of noise. Will put an example tomorrow.

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Love the idea of the crystal.  I am no expert, but looking at the mess of wiring in my computer tells me that what you have done is so neat and tidy.  Cannot wait for the tests.

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5 hours ago, Karyn said:

Love the idea of the crystal.  I am no expert, but looking at the mess of wiring in my computer tells me that what you have done is so neat and tidy.  Cannot wait for the tests.

You're right about the cabling Karyn. When I am assembling my devices I always think that I'm almost done when the electronic is working. But then I realize that the wiring takes almost the same time and with the mechanical assembly it's not better. Honestly I don't like doing the wiring, it's tedious.😕

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2 hours ago, Kevin Himes said:

My interest in this device is truly peaked! Looks amazing!

Thank you Kevin. It's also new to me because I always did my own designs but this time it's reverse engineering of a concept from another person. In fact I covered this concept of using light already in one of my earlier designs but wasn't very successful. I hope this device will perform better.

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I am facing a problem. All the wall adapters I tried out are producing excessive power hum in the device! This problem is not new. Since the rise of digital electronics, analog design knowledge got lost. Today all wall adapters are cheap pieces of sh*t coming from China. They are radiating "dirt" through the whole spectrum of electromagnetic signals. I tried some brute force approaches to kill the noise but it didn't work well. This annoyes me particulary because I have this problem with all ITC devices I make. For my applications I bought a rather expensive linear power supply to make my equipment running without noise.

@Jeff: I am suggesting to develop an ITC-ready wall adapter with a simple analog design to get rid of this problem. Since analog power upplies are barely available anymore we got to make one on our own as a standard. What do you think?

 

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Yes Andres, switch mode supply manufacturers now build the cheapest, nastiest ones they can (due to lack of effective monitoring of regulations regarding emi radiation), that float sometimes 100v above ground on both +/- outputs, and radiate vast amounts of RF. I have disposed of all my swmode plugpacks because of this,  although I will say that certain laptop dc adaptor "bricks" arent too bad, as some have a grounded negative rail, and more work is put into them in terms of suppression, as they are higher speced. I therefore use a couple of these for general work, and powering my SpeakJet unit.

Yes, for best purity, a specialised linear power supply would be best. I thought of perhaps a 12v ac transformer wall adaptor, that feeds (via common mode ferrite choke) into a remote rectifier, filter and voltage regulator. The remote items could be in the Light box perhaps - or in an interface box? Otherwise its a build of all items together incl transformer in a remote dedicated box. This may have advantages that if a metal box it is earthed, and so could be the negative supply rail.

Here is a link to a 12v ac wall adaptor, something like this would work. It still would float above earth, but maybe that wouldnt be a problem, as it wont be radiating rf cr@p.

https://www.acadaptorsrus.co.uk/uk-12vac-12v-500ma-sec-mains-ac-adaptor-linear-power-supply-a41b1200500/

Its on ebay as well. May be easier than a total build in a box, but I do like the all inclusive metal box concept.

 

 

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10 hours ago, Dr Jeffers said:

Yes Andres, switch mode supply manufacturers now build the cheapest, nastiest ones they can (due to lack of effective monitoring of regulations regarding emi radiation), that float sometimes 100v above ground on both +/- outputs, and radiate vast amounts of RF. I have disposed of all my swmode plugpacks because of this,  although I will say that certain laptop dc adaptor "bricks" arent too bad, as some have a grounded negative rail, and more work is put into them in terms of suppression, as they are higher speced. I therefore use a couple of these for general work, and powering my SpeakJet unit.

Yes, for best purity, a specialised linear power supply would be best. I thought of perhaps a 12v ac transformer wall adaptor, that feeds (via common mode ferrite choke) into a remote rectifier, filter and voltage regulator. The remote items could be in the Light box perhaps - or in an interface box? Otherwise its a build of all items together incl transformer in a remote dedicated box. This may have advantages that if a metal box it is earthed, and so could be the negative supply rail.

Here is a link to a 12v ac wall adaptor, something like this would work. It still would float above earth, but maybe that wouldnt be a problem, as it wont be radiating rf cr@p.

https://www.acadaptorsrus.co.uk/uk-12vac-12v-500ma-sec-mains-ac-adaptor-linear-power-supply-a41b1200500/

Its on ebay as well. May be easier than a total build in a box, but I do like the all inclusive metal box concept.

 

 

Thank you Jeff, this is a good idea. I couldn't find this power supply on ebay germany but I found another one at Amazon I just ordered:

https://www.amazon.de/gp/product/B01LZD8SHJ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

I'd like to suggest that I will test the power supply from Amazon. If it is working properly this will be my recommendation as an accessory for the light bridge. Lance can try out the other one from Ebay if he wants at his own risk but I think chances are high that it will work too.

That means that the light bridge will be shipped without a power supply and the new owner must purchase it by his own according to our recommendations.

 

 

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I don't know if this definitely is not a switch mode psu but the description clearly states that this unit is deliberately dedicated for audio applications and the noise it generates is specified to be 60dB below the noise level of standard wall adapters. If they can guarantee those specifications with a switch mode psu I am ok with it.

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So this is just an update of schematic and layout. As I already said I did some small modifications in the schematic again because I wanted to align the used components with the on-stock components from my favorite supplier. Second reason is that I incorporated the LM386 headphone amplifier module into the schematic with discrete components and not as a module. The circuit is so simple that you gain no benefits from using the module and using the single LM386 makes the board a little cheaper.

Schematic transmitter unit

357800374_Light-BridgeSchematic-Sheet1.thumb.JPG.33e8a3ffadf91915984753a8bfb55763.JPG

Schematic receiver unit

329472488_Light-BridgeSchematicSheet2.thumb.JPG.f007c5c831282e08febebc5c951e2556.JPG

Moreover I reinstalled a program for making perfboard layouts. I told you I was not satisfied with my previous component placing, so I decided to lay out  the design more carefully and more easily to replicate.

Component layout PCB front side

343487632_Light-BridgeLayout-Front.thumb.jpg.a67450b59cbcd592a663d84c5e4c102c.jpg

Component layout PCB rear side

506168094_Light-BridgeLayout-Rear.thumb.jpg.cea81d2cc41050a96764850531e87b20.jpg

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24 minutes ago, Lance Reed said:

Hi guys, 

Will I have to purchase a power supply lead from Amazon? Or do you want to test it first?
Let me know?

Let me test it first, Lance. Will be delivered tomorrow, thus we don't waste much time and I want to be sure you will get clear signals before I recommend it. You can already put it on your wish list if you want.

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14 hours ago, Andres Ramos said:

I don't know if this definitely is not a switch mode psu but the description clearly states that this unit is deliberately dedicated for audio applications

Yes, its very likely it is switch mode, being so slim and only 160g. Too light and too small to hold a 2A transformer, but as you say, its stated as having low residual noise, so hopefully will be suitable.

Good PCB design Andres. Nice and uncluttered.

Could you please post a pic of the waveform of the solar cell emf prior to preamp, when unit driven by tone? Id like to see the signal to noise ratio.

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