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.
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.
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.
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.