DB9 TTL to USB converter for Maynuo 9710

[Coliban]

Hello,

i purchased a Maynuo 9710 and it has a DB9 connector. Cables for this port are called "M133" and are sold for about 60€. But there are several TTL to USB converter on the market like from seed studio https://www.seeedstudio.com/RS232-to-TTL-Converter-Module-p-1684.html. Isn't it possible to take one of those since they are on around 3€?

[glarsson]

The DE9 connector (not DB9) is referenced to the negative input, so a simple TTL to USB converter will connect USB ground to the device under test. This might be ok or it might lead to a disaster. The adapters this connector is intended for is isolated (optocouplers or something else). There is no smarts in the adapter (except the USB logic) so a home built adapter will work if it is designed with isolation.

[2N3055]

Converters from Maynuo are galvanically isolated, and if you take into account that, case and the fact they are ready made,  are actually not expensive.

After you account all the expense for cables, connectors, casings, isolated converter, and work to find, purchase and assemble one, it's not really worth it for just one.

Some people had luck with low power BT modules, for wireless connection... Power available on TTL RS232 port is not specified, but few tens of mA are surely there..

Anyway, you can make one just make sure it to be isolated... It it is important to avoid ground loops and big explosions ...

[TurboTom]

Another way to reach a similar result is to use a wifi module like I showed here: https://www.eevblog.com/forum/testgear/maynuo-m9812-usb-to-serial-isolated-interface/msg1004163/#msg1004163. Maybe worth a thought?

Cheers,
Thomas

[Coliban]

@2N3055, ok, but i don't know which ground should be isolated? Is there somewhere a circuit diagram?

@TurboTom, yes i also already thought about a WiFi solution because i don't know which ground should be isolated from what. I have already build a wireless USB connection with ZigBee to control my hexacopter without a cable, so i wouldn't have to change too much.

[boffin]

i purchased a Maynuo 9710 and it has a DB9 connector.

Chances are that it has a DE9 connector.  The B shell size is for 25 pin (most common), whereas the E shell size is used for 9 (2 rows) or 15 (3 rows aka VGA)
https://en.wikipedia.org/wiki/D-subminiature

Sorry, but it's one of my pet peeves.

[2N3055]

@2N3055, ok, but i don't know which ground should be isolated? Is there somewhere a circuit diagram?

@TurboTom, yes i also already thought about a WiFi solution because i don't know which ground should be isolated from what. I have already build a wireless USB connection with ZigBee to control my hexacopter without a cable, so i wouldn't have to change too much.

Ok. Isolated converters have two grounds. One on the side of TTL (connected to Maynuo on DB9 connector.) and then have isolated data AND power that go to other side that has its own ground and data. That side goes to PC.
There are hundreds of sources of good information on Google searching for "isolated rs232 interface"

[Piefke]

@TurboTom

Hi Thomas,

I wrote a PM to you, about "...Another way to reach a similar result is to use a wifi module..."
Did you received it? I'm not shure because I can't find an outgoing message folder in my profile.
Sorry, I'm a bloody newbe here.  :-)

Thanks,
Wolfgang

[BillB]

There are hundreds of sources of good information on Google searching for "isolated rs232 interface"

And, there are actually dozens of threads discussing this very thing right here on this forum as well, that can all be accessed through a basic search:

https://www.eevblog.com/forum/projects/rs232ttl-to-usb-isolator/msg684922/#msg684922

[pelule]

I planned to purchase the Maynuo m9712b.
- before I checked the option to build the M133-USB-IF on my own (lots on info here in the forum).
I came to the conclusion, it's not worth the effort just to save $60 USD (taking risk, material, case and time into account).
So I bougth the Maynuo m9712b + M133-USB-IF in a package.
/PeLuLe

[jiarui]

I have a ITECH IT8511+, which has a similar TTL serial port.  I have tried the TTL to Bluetooth converter.  I was having a lot of problems on the PC to make the COMM to Bluetooth port to work right.  I could make it work for very short period, then I would lose the connection.  Eventually I purchased this isolated USB to TTL converter on Amazon.  I soldered a DIN9 connector to the board.  This worked without much problem.

https://www.amazon.com/gp/product/B076LNBB7P/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1