I'm having some communications issues with a CH340 UART - USB chips. They work great with a 3 - 4 foot USB cable but with longer cables they aren't working reliably or at all. The device may or may not be recognized but no data is sent if it is recognized with a longer cable.
Is this a common, known problem? I can't believe my circuit is the problem, with about an inch of parallel tracks between connector and chip.
Do you have the terminator resistors on the data lines? You can get away with not using them for short cables, but they're recommended for longer cables, IIRC.
Is the 5V power getting to the CH340 stable and appropriate?
Specifically, I'm asking about the performance of the CH340G, 6' seems like a reasonable length of cable. I'm wondering if anyone else has experienced this or if it's unusual.
I've used a lot longer cable then 6 foot with a CH340G I cut the end off a old usb printer cable I'm sure its close to 8 feet less cutting the end off .
I used the circuit that's in there data sheet to make mine.
But staying with the 9600 baud side for the moment.
It is not clear what pin 3, Rx, on the CH340G comprises, but it seems that the drive to pin3 needs a bit of consideration. R13, 10K, seems high and a pull-down resistor would seem to be required.
The circuit works flawlessly with a 3' USB cable, so I believe my circuit on the UART side of the chip is ok. It's based on a circuit in the "data sheet" with the exception of leaving out what they call a buffer/show as an inverter on the lines from the from the micro in case it's lacking in drive current.
But staying with the 9600 baud side for the moment.
It is not clear what pin 3, Rx, on the CH340G comprises, but it seems that the drive to pin3 needs a bit of consideration. R13, 10K, seems high and a pull-down resistor would seem to be required.
On the USB end, the only thing I can think of is a layout issue. The traces for D+/D- should be twins so to speak. Let us know how you solve this perplexing issue
That is to do with data integrity, but generally speaking, transporting 5V power over USB cables ia unsatisfactory because of the characteristics of the USB plug/socket and the resistance of the two power routes in the cable- some mobile phones, Android for example, need a special low resistance USB power cable to charge in the specified time. Otherwise Android phones take longer to charge.
I have some 6 foot usb cords one i paid 28 dollars for it charges and data works great. I left it at home one day and was in need of it to upload some picture i stopped at a dollar store and picked up a cheap cord it would charge my phone and data didn't work to upload