MAX232: Where to use it? | Posts 16+

Gremlin wrote:

ulf wrote: According to my understanding, the best way to install the Max in a PC/laptop would be to bring the RS232 up to the required power level... or am I completely wrong? Actually, yes, because the laptop's RS232 port should, in theory, comply with the specifications. Please send me your address via private message, and I'll send you something. CU Gremlin

Hi.

My email address is the one listed below in my posts (I don't have any other email addresses).

Chris's last response was also helpful to me.

Do his statements match the specifications that I am familiar with?

Otherwise: feel free to share information - as long as you don't need a math or physics degree to understand it, even just a little bit .

Sure, no problem!

Hi everyone,

Just to add something: The documentation for the MAX232 is available for legal download from MAXIM. Google can easily find it, or you can simply enter the part number into the search bar on the MAXIM website and search.

This component comes in several versions, including one designed to create adapters from mobile phones (3.3V power supply and signal levels) to RS232, and also a 5V version, which would likely be more suitable for this application.

The problem of energy supply, as mentioned, remains open, but I think I would opt for USB. USB ports provide 5 volts (I believe, but one should check) with a guaranteed 100 mA, and are present on most laptops that aren't too old. Simply leave the data lines untouched and "misuse" the port as a power supply.

Best regards,

Jan.

Hello,

The "problem" of powering the MAX232 can also be solved by tapping into the signal lines of the RS232 interface.
It worked flawlessly with my satellite receiver to PC adapter back then. By the way, serial PC mice also draw power from the interface.
Unfortunately, there are also pitfalls here.
http://www.hut.fi/Misc/Electronics/circuits/rspower.html



Best regards, Rainer.

Rainer K. wrote:

The 'problem' of powering the MAX232 can also be solved by tapping into the signal lines of the RS232 interface. It worked flawlessly with my satellite receiver to PC adapter back then. By the way, serial PC mice also draw power from the interface. Unfortunately, there are also pitfalls here.

Hi Rainer,

I think your cat is biting its own tail here.

If the signal pins, for example, of a weak laptop, do not provide enough power to adequately supply the opto-inputs with power -
How can one then extract sufficient power from these pins using alternative (or different) methods?

"In my opinion, the Noxon circuit already points in the right direction: instead of using the output of the Otpo stage as a switching element, it should only be used as a driver for the actual switching transistor, following the Darlington principle."
The power for amplifying the "switching power" comes from the on-board power supply (therefore, no external power supply is needed ), and the galvanic isolation using optocouplers remains in place - the goal is achieved with minimal effort.

"In my opinion, the resistors in Noxon's circuit diagram waste too much power: over 1 kOhm between the base and emitter of the switching transistor, 0.6 mA is lost before the transistor fully turns on."
Therefore, I specified 10 kΩ resistors there, which will still "effectively" turn off the unpowered transistor.

Hello Ulf,

The trick is to extract power from the transmission line when receiving, and to supply power to it when transmitting. Normally, you don't transmit and receive at the same time.

Best regards, Rainer.

Rainer K. wrote:

The trick is to extract power from the transmission line when receiving, and conversely. Normally, you don't transmit and receive at the same time.

Hi Rainer,

Okay... but then you would need to store (enough!) energy in a suitable form, etc.

So, it's a huge effort for such an adapter. Therefore, I still think... see my previous post .

Guys, guys...

You have the ultimate power source: 12V 1000A peak .

Take a 9V-9V or 5V-5V voltage converter for galvanic isolation, and the interface will have enough power on both sides.

@ulf

I guess I'll have to send you some then...

CU Gremlin.