Peculiar problem with different kind of adapter (CH340G)

Hi all!

First time poster here.
Before I begin, I shall offer up a little background info first.
Was an apprentice maintenance engineer until 2011, studied operational engineering degree until graduating this year with honours.
Keen interest in engineering, mechanics and electronics.
Have run own ebay business since 2011 selling electronic components whilst finishing my degree. I shall not however mention the business name as I'm fairly sure it'll be against terms of the forums.

The issue I would like a little help with is regarding a new stock item that turned up today that I've been testing.
It's a USB to serial adapter with a CH340G chip on board. Drivers installed flawlessly and suffice to say I've been reasonably pleased with it.

I've performed a loopback test on itself and also communicated between a PL2303HXA adapter also without any issue.

There is a couple of issues when attempting to download to an arduino whether it be an UNO, Nano or Mini pro.

Before anyone mentions it, I'm aware that the chip has the ability to switch between TTL and RS232 modes. This is determined by the RS232 pin. The internal pulldown resistor (as it is on the board) means that the serial lines idle high

The adapter itself seems to pull the reset line low, raise it and then hold it back at low. Even with the reset line disconnected and performing a manual reset, the adapter doesn't even make an attempt to transmit anything.
If I watch the Tx line of the adapter with my scope, it doesn't pull low at all i.e. I don't see a start bit.
If I used the PL2303 in the same scenario, I see the start bit and the rest of the data.

It is a little barmy because I can communicate with the arduino using the CH340G board, send and receive, it just won't download a program.

It's frustrating because I purchased 30 of these boards in order to be able to provide an alternative to expensive FTDI, lacking PL2303 and unpredictable CP2102 boards for programming the Mini Pro's so any help will be appreciated.

I've solve the problem of not communicating. Would appear that the board has a 1K resistor between it's TX pins. This means that it's unable to pull the line to 0v and only manages about 2.5V. Replacing the resistor with a 470 ohm does the trick.

It'll now program an arduino with a manual reset.
The DTR line on the board will pull low to initiate a reset, but then stays low.

Not sure whats going on there?


This happens to me, -every- time I have an issue with something. I'll sit and stick at it, get flustered, ask for some help with it online, whilst waiting for help, go back to the issue and figure it out in 10 minutes.

Turns out the way I'm trying to reset on an uno board by connecting the DTR line to the 'reset' header, turns out that there is no capacitor there meaning that the reset line was just being held low. Soon as I place a 1uF cap between the DTR and reset line, it programs and works a treat. Unbelievable!!!

Hello again.

After further testing, it turns out that there was nothing wrong with the adapters, at all, and that it was just me being stupid and completely Novice to arduinos.

I can confirm that they work absolutely fine standard, as they are and work perfectly well with the mini pros with pin for pin compatible layout. I do have them advertised and available on a well known auction website should anyone be interested but there is limited stock however.


Where can i get a driver for the ch340g?

Tired of manually resetting Arduino Pro Mini while using a PL2303 without the DTR pin to upload sketches, I ordered for the CH340G USB adapter with DTR pin.

It is pin to pin compatible with Arduino Pro Mini, the CTS pin left disconnected.
Uploading works perfectly without the hassle of pressing reset button.

Who did you buy that from if you don't mind me asking?

I get mine from this seller:

Found drivers here, but not an English website. Fairly intuitive though.

Thanx Bill
you helped a lot,that worked.

On forum below, I found the driver for my arduino nano V3 card with a chip CH340g for USB-serial link (not a FTDI chip, apparently Chinese clone chips are automatiqement blocked by last updated windows and FTDI, but hey I'm not the right place to mention here)

Fenchurch Thursday, December 02, 2010 4:43 PM Reply
Found this to work on Win7 64bit probably works with other os's as well.
Thank you Fenchurch !!!!!!!

I said that this driver works under Windows 7 64 bit.

I recently bought a CH340G USB to Serial adapter which didn't have a DTR pin. I wasn't very good at pressing the reset button on the Pro Mini at the right time, so I investigated adding DTR to the adapter.

I discovered that the reset signal is available on pin 13 of the CH340G chip. I carefully cut away the heat-shrink from the pin and soldered on a wire. I attached this wire to the spare lead in the supplied cable and this goes to the DTR pin on the Pro-Mini.

It works perfectly, and I no longer need to press the button when uploading.