If you are looking at this page, you probably feel like I did when I tried to run a self-powered PIC programmer with my notebook computer. Yes, the serial port was the ultra-low-power type and wouldn`t provide enough current to power the programmer. The problem was clear and so was the solution. I could have modified the programmer to get the power from somewhere else, but in the future I�d crash with the same wall. I needed something to interface the low-power serial port to the hungry programmer. I didn�t find anything in the web, so I decided to design it by myself. Again, MAXIM was there to help with one of their smart engineered ICs, the MAX205:

MAX205 Datasheet (PDF Format)

The MAX205 is something similar to the popular MAX232 but these are the good news:

• It hast 5 receivers and 5 drivers instead of only 2 + 2.
• It does not need external charge-pump capacitors !!

If you connect the TTL outputs of the RS-232 receivers to the (TTL) inputs of the RS-232 drivers, you effectively get the original signals with plenty of current for any serial-powered device with an extremely simple circuit:

Don't forget to connect the shields of the DB9 connectors to the circuit�s ground. The RS-232 input signals don`t need to be boosted, so they can be simply wired pin-to-pin. All you have to worry about is where to get the 5V from. As I`ve already done, you can use the notebook`s AC adapter and a 7805 shunt regulator.