Isolated USB to serial converter 6 in 1,  YN-4561(I)  RS485/RS422/RS232/TTL - Page 1
Forum section: electronics / beginners

author: Coyote
author_rank: Contributor
timestamp: April 04, 2017, 12:01:33 pm
content: Hi everybody,Yesterday I got a USB to RS232/RS485/TTL converter from China. The major importance for my work on the field is that this device is galvanically isolated, so before testing it in real environment I have made teardown inspection.The entire device has four isolated sections: USB, RS232, RS485/RS422, TTL. The power comes from USB port and then two DC/DC converters (B0505S-1W) are used to supply sections RS232 and RS485/RS422, meanwhile the TTL section is supposed to be powered from host side.The USB to UART bridge controller used is Silab's CP2104, the Win7 had automatically installed all the drivers. All input signals are protected by TVS.The RS485/RS422 section has four TVS, two Sipex's SP485EE transceivers, 74HC14D inverting schmitt trigger and two opto couplers 6N137.The RS232 section has two TVS, the Sipex's SP232EEN transceiver, two 6N137 optos.The TTL section has three small TVS and two 6N137 optos.The USB section has CP2104, two 74HC08D quad AND gates.OK, so far nothing to be worried about, but wait a minute. I can see two jumpers on board. The first binds together USB GND and RS485/RS422 GND, that's not what I was looking for. My goal was to break the ground loop from my PC and industrial device. The second jumper seems to connect +Vcc from USB to a contact named NC, the manual says in red bolded text: Do not connect anything.Of course, the manual has no mention about the jumpers. I will post what I have found out.I have checked with multimeter and draw a simple jumper settings. The default setting is that USB GND is connected to RS485 GND and +5V from USB is forwarded to a pin named NC (Do not connect anything). I have placed jumpers in opposite setup, so now the two grounds are separated and NC pin is now really an unconnected pin, I don't want to share the USB 5V to outside.Another disappointment is that RS485/RS422 section has only two opto couplers: TX and RX and no RTS. The TX/RX switch is now implemented by some delay timer derived from TX signal, must be that 74HC14D schmitt trigger with caps and resistors that is doing TX_EN for RS485 transceiver. Will see if it is working, I have expected a full RTS control when buying,....

author: retrolefty
author_rank: Super Contributor
timestamp: April 04, 2017, 02:18:12 pm
content: Yes, the term isolated can mean different things from the marketing department and the design department. True galvanic isolation requires isolation of all signal, grounds, DC/DC convertors, and power leads.Thanks for sharing your experience with the product.

author: Coyote
author_rank: Contributor
timestamp: April 10, 2017, 12:16:06 pm
content: UPDATE:I have tested the RS485 transfers with TeraTerm using XMODEM. I tested transfer on low speed 600 bps and max. declared speed 115 kbps. Even if the TX enable is derived with a rudimentary timer made of logic gates, it works good. I was able to send at even higher speeds, up to 460 kbps.This device can work also as level converter between connected devices where USB port is used just as power supply. It's a practical all-rounder PC<->Device /or/ Device1<->Device2, and it's cheap also, after all not so bad deal as I was thinking at the first look.