Below is a howto on how I made my FM transmitter use power from my PC, while using audio from the soundcard at the same time! It is still a Work in Progress, but please comment on it, I am open to suggestions
You seem to have things a bit mixed up; what exactly are you trying to do? If you're using a car to power a mains device, you can buy an inverter that takes the cigarette lighter 12v DC and converts it to mains 230v AC. If you want to draw from a computer PSU you can get 12v or 5v easily enough; how many watts will you be drawing?
I'm sorry if I come across as a newbie to electronics, because I am! I notice you come from scotland, so you'll understand that I am currently doing my standard grades in physics, and that's all the experience I have I'm afraid. I think it would actually be better if I did in fact use the PSU option. as for watts, I'm not entirely sure how much I'll be needing, I did a little research as to the standard wattage drawn, but I couldn't find anything. I can tell you, however, that it also uses 2 AAA batteries, does that help? thanks john
2x AAA means that it uses 2x 1.5v, and very little current. Off the top of my head I'd guess attaching a 150 Ohm resistor to the 5V line would do it, do you have access to a multimeter to test voltages?
If you can, grab a handfull of resistors, you should know how to chain them to make the value you need
no, no no! First of all, if you don't know what you are doing, DON'T mess around with mains power. It's deadly. Secondly, If you just want to run something of mains power, simply get a small power supply that you can set to 3V. Shouldn't be hard to find. Using resistors ONLY works when the load is constant (Like LEDs). If something have variable current draw, the input voltage will wary when the load varies (Study Ohms law, and you'll see why). If you REALLY need to use a PC powersupply you could get a hold of a voltage regulator. This is slightly more complicated than just adding a resistor, though.
Thanks for the info. If you were to embark on this project, what would you recommend? Am I right in thinking that using my PSU instead of the mains is a much safer alternative?
QFT If you have a "cigarette lighter" adaptor the easy way is to connect it to a 12V DC supply, either a PC molex (yellow & black wires) or any 12V DC wallwart (if the radio runs off 2 AAA cells I can't see it drawing much current). You'll need to work out which wire in the lead is positive - I assume the *** plugs are tip positive in a negative earth vehicle. And make sure you don't remove any bit of the *** adaptor that is knocking the car 12-14V down to a lower regulated voltage. If it's part of the plug best way is to buy a female *** connector and wire that to your 12V supply. Then just plug & play.
I'm a bit unsure what you are actually truing to do. If the thing run of a cigarette lighter plug then you could just wire it to the black and yellow wires of a PSU. (The yellow go to the center of the plug). Just be aware that some PC PSUs won't start unless they have enough load. You will also need to short the green and a black wire for the PSU to start. (Assuming that there is no computer connected. If there is, you don't have to worry about this) If the transmitter is able to run of 2xAAA batteries, and you are going to just stick in two wires instead of batteries, then you would need 3 volts. The easiest way then is to get a power supply (Wallwart?) That is able to put out 3V DC. Indeed. Not only is the voltages safer, but a PSU also have short circuit protection
If it is an FM transmitter with a 12v cigarette lighter attachment as well as batteries (i.e can be used either plugged in to a car or running from batteries) then by far the easiest thing to do would be wiring the cigarette lighter bit to a 12v line in your computer. Because they are both 12v you don't need to do any voltage conversion then edit: What they said above^^ I should have learnt by now that people tend to have posted if I leave the page for an hour
cupboard: thats exactly what it is Smilodon and cpemma: I think I will go for molex as I have tonnes of them in the computer to connect to. I'll post back what happens, until then - hold your breath people
Update: I tried it and it works! For reference's sake, I put the red cable (the one that originally was the pole at the top of the cigarette lighter attachment) in the far left (yellow) hole, and the black cable (the one attached to the side of the cigarette lighter attachment) next door in the black hole. Now all I need to do is buy a male molex and solder it all together
I'm curious, are you attaching an FM transmitter to a pc? If so, then why? Is it so you can play mp3's?
Well the PC I'm connecting it to is actually a Linux powered, automated shoutcast DJ. So by me attaching my FM transmitter, I'll be able to listen to what is playing around the house
I've finished phase one of my project. Here are some pics (sorry about the quality): What you need: an FM transmitter (I got a generic one off ebay) an old device with a male molex (I used an old floppy (or was it a zip drive - I can't remember)) a soldering iron a precision screwdriver set here is the FM transmitter I bought off ebay: It came with a "Car adapter" to power it, I took off the car adapter part, and stripped the cable. Find an old piece of hardware with a male molex on it (hard drives, CD rom drives, Zip drives, and Floppy drives all have them) Keep the enclosure of the hardware - we'll use it later Take the batteries out of the FM transmitter, and use a precision screwdriver to remove the tiny little screw, and pull the top part of the case off Use the soldering Iron to de-solder the battery pack from the board, it is joined by two rather large terminals to the right of the white button. (By the way, does any one know what the white and green cables could be? I think the green one is the antenna...) De-solder the molex from the hardware, make sure you don't break any of the molex pins, the other ones don't matter. Solder on the red and black cables from the car adapter as shown (red to the left, black to the right) on to the molex. Plug the female molex in the computer into the male molex you acquired from the hardware, make sure the PC is turned off at the time. Plug the audio cable into the sound card at the other end. I had to take one of the PCI plates out of the case to have enough audio cable to do this. I may use the built in speaker in my machine to allow the FM transmitter to transmit music and still have the soundcard free! Sorry about the bad image quality, I have tried to enhance the blur and colour as best as I can. I hope this makes a good future reference for others I will post updates on the transmitter as they happen.
Im pretty sure theres threads kicking about dealing with this same basic concept: powering something off the PC, no data required. Just mind you're not choking your PSU, it shouldn't if its just AA battery current you're dealing with but the number 1 problem in crashes to do with my PC has been PSU problems. I'd also add that what you were talking about in the op is available it's called an AC to DC transformer, know how those big box-plugs commonly used in things like phone chargers. You can buy voltage/polarity selectable ones that come with multiple connection types for about £12. Its not impossible to make something like that but unless you have access to some copper wire, a strong magnet and solid experience in transformers, it aint suggestable. Mains isn't really something to go playing around with if you're at all uncertain what you're doing, I've survived a couple mains shocks though, infact very recently I got a really bad one off a 200watt amp, guitar earthing came loose and whenever I went near the mic it just earthed itself on it, just put a plastic bag over the metal casing though and played through it.
wow, that sounds pretty bad Because It's connected to the PSU, the worst it could do is give me a shock at 12V The device was for my computer anyway so going the PSU route was better all round.
