Engineers Wanted!

I need someone to help me design the power supply for an electrical circuit I'm engineering for my car. Anyone with a good grasp on current limiters and transistors would be of great help. If you want more info, post up.

Details?

Circuit consists of two PNP transistors and an NPN so far. The circuit is designed to turn on two motors which operate a sliding plexiglass panel. When that panel reaches a set point, it opens an interlock to turn off the motor. I haven't worked with transistors in so long that I don't remember if they have a current limitation on them or not. I want to power the circuit on a normal 12V car system. What I need to know is whether or not I need special transistor or if I need to design a power supply to limit the current to the transistors.
Here's my schematic so far.

http://img93.imageshack.us/img93/7785/circuit6os.png

Use a S.P.D.T. lever switch. Self explanatory with wire output and forget all that electrical stuff out. All you need are two SPDT lever switches, a DPDT switch and some wire. Why make it more difficult than needed?

http://www.allelectronics.com/cgi-bin/item/SMS-204/700/MINIATURE_SPDT_LEVER-ACTUATED_SWITCH_.html

If I do just the switches I would have to hold down the Normaly Open switch or use a toggle. I want to be able to press a momentary button and let the electronics do the work, also I'm still working on the portion of the circuit that closes the panels. If I want all that to work off of one switch I need a this circuit to control everything.

Use the SPDT lever switches along with a timer circuit. Set everything up, and time it while hard wired. Say it takes a total of 10 seconds to open or close the panels. Set the timer to 15 seconds. Duration doesn't matter because the SPDT lever switches will shut the circuit off at the desired location.
Timer circuits are a basic fundamental of electronics. You can use a 555 as an example (very easy to manipulate). If you use a 556, you can use the dual 555 as a delay. Example; Push momentary button, 555 #1 is triggered. After x amount of seconds, the first 555 triggers the second 555, opening the panels. Have fun. Google the 555 IC, plenty on the web.

I know a little bit about the 555. I've worked with it some but it's still basically a transistor circuit. The circuit I designed would be able to use the SPDT lever switches as the normally closed switches (that's what they were to begin with) and they would act as the interlock like you mentioned. Because the circuit is designed to be an open hold type circuit based of a relay circuit designed to do the same thing, it eliminates the need for a timer by opening the pathway to start flow through the transistors and using a sample from the transistor output to hold the transistor open untill an interlock (the SPDT lever switches) are opened and that stops the flow of electrons through the transistor which turns off the transistor. there will be a second set of PNP transistors to control the closing portion of the panels. All together there will be 2 SPDT interlocks per panel. My circuit is designed to handle two panels (4 interlocks) and I need to open 8. The idea is to recreate this circuit so that it can operate all panels from one switch. I don't want to use relays because they click so that's why I needed to know current limits for transistors. If they have a limit then I need to design a power supply that will convert the cars electrical to something the circuit can use.

Every single chip is built around transistors. Correct me if I am wrong on that statement. I think the Pentium III has something like 25-million transistors. When you say you have not worked with transistors in so long, how many years could that be? Your 22. Maybe if you were 74 and have Alzheimer but something as basic as that and you want to tackle a design project like this :banghead:

If all that you are worried about is the click, insulate it or hide it deep somewhere. Those motors will produce enough noise that you won't even hear that .1 second click. Otherwise get yourself a solid state relay. All the power of a relay, none of the click. Pricey though. As a final help, look up IC monostable multivibrator, which is built around the 555. As you can tell I like the 555. It's easy to use, cheap, and has 100's of configurations.

"I don't want to use relays because they click so that's why I needed to know current limits for transistors. If they have a limit then I need to design a power supply that will convert the cars electrical to something the circuit can use."

Ok, I will finally answer this as it seems to be an issue. You should know with your knowledge that every transistor; PNP, NPN, MOSFET, J-FET, etc has a current and voltage limit. Open up your digikey catalog and you will find a simple 2N3904, which is a basic NPN has a maximum rating of 200 mA. How many amps does one motor draw? 5+ amps @ 12V? Better do your home work. Your gonna need some MOSFET's for this bad boy. I have given you my idea which is a simple, reliable way to go. There are plenty of electronic forums out there just like this automotive one, take a look @ one of them. When you complete your project, I would like to see the end result. Curious to see what you come up with. I think this is too large of a project to design on your own. Don't forget that you need resistors, capacitors, etc. Why reinvent the wheel?

I will say good luck. Don't let me push you away from this idea. Great to see people still getting dirty with electronics. These days it is so easy just to go to the store and find what you need made in China. Post your findings and I will give you the :thumbsup:

Will the circuit only pull the amount of current that it needs (unless something shorts of course). I hadn't thought of solid state relays but you're right about the motors only using about 5 amps. I'll need to limit current to each of those as well. You said I would need mosfets for this circuit. Do you mean to limit current or simply to handle it. I assume that you're talking about high current mosfets.
Yes, you're right about transistors being in every micro processor there is. What I meant about not working with them was that I haven't designed a circuit in several years that uses single transistors or small 555 type IC's. The Air Force only taught me so much when it came to electronic principles. I wish I had more indepth knowledge than I do (or that I could at least recall everything I learned). I know I need help designing this, that's why I asked. It's been too long since I needed to really use component level signal tracing or design. Most of what I did with the Air Force consisited of removing and replacing whole circuits rather than components.
I started looking into information on mosfets and the IC monostable multivibrator like you said. I'll draw up a diagram in the next week or two. I'm still researching what I need to do about my currnet probs. Hopefully I'll have a working model before it's over with. I don't want this to become a dead end project when I know that something this small could be done.

Very well, I will watch for the post. Keep in mind that 5 amps is a lot of power, especially if you have a few motors on the same circuit. Circuits that contain MOSFET's only push the current that is needed. If you have a 35A MOSFET and use 2A, then a small heatsink is needed. Likewise, if you use the same 35A MOSFET and use the full 35A, you would need a trash can (maybe not that big) as a heatsink. That is why some heatsinks have a power rating (in watts) on them.

LOL trashcan! That's funny.