12 - 5V converter - check it plz.

Yesterday, I was figuring out how to make the perfect 12+ to 5V converter with the fewest parts possible. So far, this is my circuit configuration:

I use a 2N4401 NPN transistor, I connect the 12V to the NPN's base through a 2.2K resistor. I grounded the NPN's emitter, and the NPN's collector is connected to VCC through a 4.7K resistor.

I connected my DMM to the collector (of the NPN) and ground. It seems that the voltage levels are highly acceptable (4.7V when 12V is disconnected and < 1V when 12V is connected), but I am more concerned with the current levels.

In order for me to make this circuit successful, I need to adjust the resistors so that I can get a logic "1" and logic "0" coming from the collector. I also want every IC that is connected to the collector to take the signals as logic "1" and logic "0".

I want to eventually use the serial port to transfer data between the PC and the microcontroller. I could end up making my own modem.

What is the best current amount to use for a logic "0"?
and What is the best current amount to use for a logic "1"?

or better yet, what are the optimal resistor values?

The pull-up resistor value depend from logic IC family: for 74LS serie You can go up to 20..30k, but the CMOS-serie happy with 100k. (PIC-s also). For log.0 the 0,8..1V acceptable, most BJT-s cannot go lower.

Try drawing a circuit of what you mean, and explaining better what you actually want to do - I think you're over complicating what you need to do?.

If it's just to connect a PIC via RS232 to a PC without a MAX232?, it's easily done using just a single resistor - the BASIC Stamp does it that way.

when i check the logic levels on my computer 15 was 1 and 0.5 was 0
hope this helps

danielsmusic said:

don't jude me by old i am!

Click to expand...

Daniel, do you mean to say "Don't judge me by how old I am!" ?
Did you notice that you left out a "g" and a "how"? I'm not picking on you - I just think you will get more respect if you clean up your signature.

A teenybopper?

Nigel Goodwin said:

If it's just to connect a PIC via RS232 to a PC without a MAX232?, it's easily done using just a single resistor - the BASIC Stamp does it that way.

Click to expand...

Yes, except my uC is the AT89C2051, not a PIC.
What value does the resistor have to be?
I don't want to blow anything up in the process.

mstechca said:

Nigel Goodwin said:

If it's just to connect a PIC via RS232 to a PC without a MAX232?, it's easily done using just a single resistor - the BASIC Stamp does it that way.

Click to expand...

Yes, except my uC is the AT89C2051, not a PIC.
What value does the resistor have to be?
I don't want to blow anything up in the process.

Click to expand...

It relies on the protection diodes in a PIC, presumably Atmel processors have them as well?. All the resistor does is limit the current to a safe level (spec on the diodes should be in the datasheet), I seem to recall 22K is a common value for PIC's.

You should also be aware that a MAX232 inverts the data, and the processor is designed accordingly, so using a simple resistor means you can't use the hardware UART, but it's trivial to write a software one, which you can use inverted or not.

Atmel's datasheet doesn't whisper a single word about input protection diodes nor a safe amount of current for them. They just say to keep anything more than 0.5V above the supply voltage away from there.

audioguru said:

Atmel's datasheet doesn't whisper a single word about input protection diodes nor a safe amount of current for them. They just say to keep anything more than 0.5V above the supply voltage away from there.

Click to expand...

Rather crude! - in that case add external diodes!.