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Disco Dance Light
Guess you kind of saying its not worth it to build an intercom on your own. I am totally ignorant when it comes to wireless transmissions, radio circuits. Its my next step in learning. I was thinking an intercom project would be a good introduction to it... Sounds hard.. I was wondering too, as I don't have one. Does making this type of circuit require an oscilloscope?
An oscilloscope doesn't make building it any easier but it sure makes figuring out why it doesn't work later much simpler. The things that wouldn't be in my scrap boxes now if I had had the proper tools when I was younger.....

That said though, Roman is right, if you really just want an intercom there are devices and apps etc that will do the job much better than anything you can build, and are probably cheaper too. There is another thread on here where I mention phone systems and although mine has fallen into neglect, its great for calling between rooms or buildings on your property, or making your cell act like a cordless phone or have a door phone or any other combination you can think of to make communication between different devices completely homogeneous.

I'm in the process of rebuilding mine to be pbx-less if thats a word, where I don't actually have a server at my house and just use extensions and trunks off a completely hosted system where I get my lines from. I'd be glad to show anyone who is interested what I am doing and how it works.
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If things weren't meant to be modified, they would not come with wires attached.
Oscilloscope is a great tool to learn about electronics. I sell Siglent brand, they have very inexpensive models, unfortunately high USD makes them more pricey here in Canada.

If you are truly interested in RF development a good power supply, LF/RF signal generator, counter are good tools to start with to save you hours of guesswork.

Start with RF detector, easy to build. It is important that diodes are germanium (hard to find):

If you want something more sensitive, get a so called "bug detector" or "bug finder", e.g.:
This is non-selective receiver, it will tell you if your circuit oscillates at all.

Counter - tells you what frequency are you transmitting on. You can also measure time, voltage and temperature drift of your transmitter:
When measuring frequency of simple oscillators, do not attach counter directly, but inductively. Make an antenna, and "receive" the frequency.

LF signal generator.
but this will do:
Thank you Roman for all your advice and links. RF is really something i want to experiment with. You can do so much with it. I am not ready yet to dive into it, but I will sooner or later, and I will refer to these links to get me started. I already checked them out, and those devices on ebay are pretty cheap. When I do by an Oscilloscope I will definitely buy from your store. They are very expensive especially for the high frequency ones. I originally thought you can just try to copy an intercom circuit on the internet and there you go, but sounds like its so much more then that.
I made a few attempts at RF stuff when I was younger but really didn't have the right tools at the time, so lost interest - now there are so many pre-made modules its a lot simpler and you are not actually building the "radio" part yourself but just integrating it so its a lot easier. It's great to understand how it all works so when you see consumer electronic claims you can judge if they are real or fantasy since you understand the physics behind it, or you can pick the right module for what you want to actually do.

The digital and low frequency analog is a lot simpler for a beginner since every stray piece of wire doesn't act like an antenna, capacitor and inductor of significant magnitude all at the same time at the frequencies you are working with. What amazes me is how many components are just part of the copper on the pcb now, since you only need a few zigzags of copper at those frequencies to make a significant impact on the circuit.

Unless you enjoy frustration, I would start with low frequencies, and/or digital till you get more comfortable.
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If things weren't meant to be modified, they would not come with wires attached.
So its building the circuit so the components dont interfere with the Rf that makes building a Rf circuit difficult. I guess you would have to shield the copper and components and keep them far apart.
its more than just that, wires close to other wires act like capacitors, bends in wires or traces act like inductors, even leaving long leads on a component makes it act totally different than cut short.

you could take all the material out there on how to do lightning protection for buildings and just scale that all down a couple thousand times and it applies to microwave frequencies right on pcb's - things like no sharp bends in wires, don't keep things close together etc etc, all just scale right down but still apply. Lightning is just a high frequency spike and that's why all the same principles apply. Weird stuff starts to happen at those frequencies and air might be a better conductor than copper depending on the geometry.

If you remember the old 300ohm twinlead for tv antennas, the same principles scale down at gigahertz frequencies to parallel traces on a pcb acting like the same sort of transmission line circuit and its impedance has to be matched at the ends or you get signal reflections back and can have standing waves within the traces themselves. Nightmarish stuff when you are trying to make something work and have no idea half the effects are even occurring in the first place.

Perfect example of the weird things that happen at those frequencies is how you can look through the holes in the metal of a microwave door and not get any heating effect passing through. They happen at all frequencies but the effects are just more observable at those frequencies. Another analogy is how you have a waveguide in a microwave coupling microwaves into your food, if that impedance is not right (food is not present) the waves reflect back into the waveguide (which is really just another type of transmission line) and when you get a standing wave in there the microwave tends not to like it much.

Not trying to discourage you from playing around in those frequencies and there certainly is a lot more cheap parts and reference material than 20yrs ago, but its just not the same as running things at near DC, and there are a lot more things you have to take account of other than just the ideal circuit on paper. Basically take your nice simple circuit on paper, then change every wire on it into an inductor, then draw in a capacitor from every inductor to every other inductor in the whole circuit and thats what you analyse, not what you drew in ideal form.

If you stay under a watt or so you won't even cook yourself if things go bad Smile
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If things weren't meant to be modified, they would not come with wires attached.
Darrin, if you want to build the circuit so much, I have designed one for you, should work at 91MHz:

This is basically what we used with my fried 25yrs ago to communicate, except at that time it was more trial and error and I had no idea how to calculate air inductor value or that piece of wire is monopole antenna and what is it's capacitance, so hope this article saves you some time.
Hi Darrin, The light looks real good. The nice thing with Arduino is you can always try different code to test new effects.
I tend to build two of a device once I get close to what I want the finished device to be; leaving the original prototype on a breadboard with a label and the as_done code version. That way you could try to add the extra "bells and whistles" and if you are successful, update your light.
If is still fully functional and you learned what doesn't work.
It is good for Roman as well as I am sure he will not mind selling us double the parts Smile
Hey Bob. Just noticed your reply that you made many days ago. Thankyou.
Sometimes I read replies before I go to work, and I have no time to reply, I then come home later, and everything is already marked as read so sometimes I overlook the replies I have to make. Ive done it a few times. I was just browsing my previous threads and found this. I remember you saying this before.
That is a good idea to make 2 and label your code. Last year I made a Metric Clock that the arduino kept time by a pulse to a bunch of cmos 4026 chips. I originally had it to lose only around 10 seconds a day, then I kept changing the code to try to improve it and I only made it worse. Left it on the shelf. Now I do not know what was the best code I had.
I am going to make a charlie cube coming up. The original design requires common cathode rgb's. Roman sells common anode, so I had to order them from China. When they get here I will be making 2 of them.

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