Who would like to build a challenging schematic?

Alright, here is what I'd like to build, but my electronics experience equals to a few LEDs, some resisters, capacitors, and a 555 timer and some skimming of Electronics For Dummies. I'm building a truck and I want to put headsets for all four occupants on an intercom system but also allow for them to choose the ability to listen to the radio through said headsets. Now drivers headset will be using a VOX and will be used for CB, phone, and intercom communication, changing from CB/phone to intercom via toggle switch and SPDT relay.. (The CB is has a Bluetooth option built in and will be a single function.) I've tried to visualize in my head how to build this, but, to be quite honest, have no friggen clue what I'm doing. So I'm asking for your help. I understand components and what they do for the most part, but I don't know what I need or how to arrange them or build a schematic. So if you would, please, design a schematic that includes a 4 way intercom system (allow for all users to talk freely) with an integrated override switch that will automatically switch all users to intercom when position 1 begins to speak. I already have the VOX needed to throw any switch. If you could also include the relays necessary to allow positions 2-4 to choose to listen to the radio or intercom system. This would let them decide if the wanted to talk to each other or not. I greatly appreciate anyone who is willing to accept this challenge. I am always open to multiple opinions, so please submit any design and parts list. If you have any questions please ask. Thank you for reading and any help you are able to provide.
-Andy

This sounds like a nice project. Not too difficult. However it may be possible to purchase an off the shelf intercom and have most of the components and switching done for you. If not, I think that microprocessor controlled switching and perhaps a digital voice routing system may not be too difficult if you reach the right people. I am an analogue designer / inventor, mostly in the HF radio industry. Thus I am not much help with microprocessors (much to busy on analogue ) However this may get a few people thinking as there is possibly even a market for such a thing. Good Luck

They are such units available and they dont use relays but im not sure about intercom use or group call Something slong the lines of intercom units they use for motorcycle instructors mighy be your answer to this So id start in that direction

There are currently switching boxes available for vehicles with multiple headrests which utilise infra red transmission for passenger use for headphones and tft monitors but thry are listen only

Hi Andy,
I would suggest the best option in the short term is to buy an off the shelf system that is close to your requirements (within your budget), and modify it to your own specification as and when you gain the electronic knowledge and experience.

As a beginner at electronics, building the complete system you describe from scratch is really not practical. If someone gave you a bespoke circuit and a kit of parts and you built it, there would still be a considerable amount of tuning and debugging to carry out, which would require a good technical grasp of electronic principles.

But, I am giving you full marks for being ambitious ! Everyone has to start somewhere, and you have made a small start, but you need serious determination to keep you going to the place you are ainming for.

Old (allegedly) Chinese proverb: "A journey of a thousand miles begins with but a single step."

To obtain an understanding of electronics, I offer the following sites which offer instruction and advice for beginners. Have look at a few, and discover which one(s) suit your approach.
Start with simple projects and work your way up. We will always be here to offer the best advice and wisdom we can.

www.learnabout-electronics.org/index.php - Descriptions of components and principles, good diagrams, animations, & fault-finding techniques

http://www.satcure-focus.com/hobby/index.htm - Useful range of ideas tutorials circuits links etc

http://www.allaboutcircuits.com - a series of online textbooks covering electricity and electronics

http://electronics-for-beginners.com/links.php

http://www.hobby-hour.com/electronics/ - Teaching from basic principles, resistor code calculators, projects

http://www.radio-electronics.com - useful information and tutorials

http://www.electronics-tutorials.ws/index.html - plus calculators & tools

Here's an example of a kit to install in aircraft. These have been used there for years. There are some very nice functions available including pilot isolation so that he may talk on the radio while the passengers are still listening to music, voice activation, and multiple music inputs. There are portable and panel mounted versions. Don't reinvent the wheel.


http://www.pilotmall.com/product/SoftComm-ATC-6PS-6-Place-Panel-Mount-Intercom/intercoms

Wow, well that's an awesome find, and it's exactly what I'm looking for. I'm just not sure what voltage it runs. I know the aircraft I work on are all 24-28 volt systems. Do you have any insight?

12 volt systems are readily available. Many small aircraft are 12v you may find that they have set it up with multiple inputs so that one unit can run on different voltages depending on how it is connected. Do verify the unit you are looking at is 12v capable. Many portable units have batteries so that speaker output would matter not system voltage, but you should have no trouble finding 12v. Permanent or "panel mount" intercoms would be the way to go unless you really wanted to use it different vehicles. Try Trade-a-plane, Aircraft Spruce, Univair, Chief Aircraft Inc, for a variety of brands and prices. All those companies predate the internet , but all have websites now. Pair the intercom with noise cancelling headsets for a very nice system. In my experience the cheaper/heavier systems are adequate unless you are wearing them 8-10 hours a day or are an audiophile. Four headsets and 4 place intercom for $600-700 may be possible, on the high end you could spend 10 times that depending on brand and features. Very nice and light headsets can run over $1000 each. These companies tend to build for pilots so most offer some very nice equipment if you want to spend the money. Look seriously at the voice activated intercom as if the standard is used then a push to talk switch must be installed for each person to allow their voice to be heard. On the other hand you may want to just have those switches for the front seat and put the mother-in-law in the back ;~)

One thought occurs to me: the driver of a road vehicle should never wear headphones, as he needs to hear the sound of other vehicles around him.

If you are driving with headphones on, happily enjoying your music, and the truck you are about to hit sounds his horn and you don't hear it . . . you can figure out the rest.

Idealy the driver wouldnt be wearing headphones However if that was the case Then buetooth earpeace singular would not be legal What you should be considering is wired headphones in the vehicle by that I mean hardwired to the connecting equipment This could be dangerous to passengers if there was to be an accident as they could be strangled by the cable Hence why they use infra red transmission and bluetooth which is typically handsfree and no connecting cables other than to the transmitters Also if was so dangerous consider that motorcycle Instructors and learner drivers on mopeds, scooters, would not be able to instruct or be instructed

The other that is relevant is if headsets were a danger when driver What happens to people have hearing disorder ie partially or completley deaf They are still legally entitled to drive



I think the only concern re saftey here is no connecting wires which might possibly cause strangulation This is also why its particularly hazardous to fall asleep in bed with headphones on as you may not wake up and can easily strangle yourself with wired headphones

Did you notice the picture that Andrew included, upside down? In my state that bumper would make sure it was not street legal. I don't think strangulation is a big concern, most have coiled cords so there is a lot of give, 4 point safety harnesses and seats that are crash worthy at 20 gs are common on aircraft. There is some concern with the wires hindering a pilot escaping a wreck. Generally the receptacles are mounted in the center on an aircraft that has doors like a car and on the sidewall when pilots have to exit back through the aisle. The connector plugs do not lock so a person that was pulling at the wires would easily disconnect them. As for car horns I would not be concerned with them but would be concerned with sirens. Being about 45% deaf from years around turbine engines I don't think I would be any less safe with a headset on, at least no less than the kids that drive around with the stereos you can hear a block away. I can see a big concern with a motorcycle as the driver tends to get separated from the vehicle in an accident.

AGREE, its still far safer to use infra red then multiplex the audio side to each passenger There are comercial systems available It would be much easier to adapt this to your specification and far cheaper unless you just fancy the fun of building a unit, which is understandible plus you learn by building which has always been my argument, not to mention if you build this then Ive always maintaned you develop a far better apreciation for the maintance aspect of this rather than producing a throw away item

These are strictly my own views Others may differ

Thanks everyone. I'd just like to be clear, and I am in no way trying to be rude, this truck I'm building is primarily for off-road use only. This intercom system is meant to be used off-road where engine noise from high RPMs and constant vehicle imput adjustments makes a hands-free instant communication just one less thing to worry about. I'm also just doing this for the sheer fun of my passangers to be able to goof around with the headsets. Being a helicopter mechanic in the military, I know the fun that is associated with playing on a headset, and for those who don't get to experience this on a normal basis could something to remember. If you knew all the BS that was going into this POS truck, you'd probably just shake your head and walk away. It is too over the top. Anytime you have a $400 '86 S-10 Blazer with a 383 V8, 1ton running gears, 12 and 24 volt electrical systems, and a winch that could easily lift 3 of the vechicles it's mounted to, you're dealing with a person that's got way too much time and imagination on his hands. I'm not crazy enough to put myself or anyone else in a situation where my driving would be concidered dangerious, I'm just out to have a good time and enjoy the wonders of nature.