Sketch Uploading: USB to TTL Serial Converter

Hi Guys,

Bought an arduino pro mini the other day and it arrived today. I intended to stick wires in , not realising it didnt have USB conversion in place. So now I'm stuck :S .

I would love to buy the cables pre made but I live in the UK and the price for the cable is £26 after P&P and VAT. The breadboard on sparksfun is similar since I'm not in the US it is a whopping £10 just to get the cable shipped!

So I'm left to make it myself. Now over here , I had a look on ebay for the arduino converters and , unsurprisingly , they are not there. So looked for USB to TTL connectors , hoping to find something on that , woohoo , found something! Mainly Asian manufacturers but a few UK distributors.

Before I buy one though (I'm looking at something like this I notice there are only 5 pins.

So my question is:

With these 5 pins , How do I connect those to the 6 on the arduino? Presumably one is duplicated?

As in:
found on Online Casino Sites In India 2023 | Best Online Casinos To Play At

Can't follow that guide to the word since the cable he is talking about isn't in any UK ebay shops. But I DO notice the cable has 5 outputs to the connection to the arduino.

I do see on the pin diagram on the ebay product , some of the outs match up with holes on the arduino where the 6 pin connector would go.

Thanks in Advance :slight_smile:


EDIT: I meant £10 for the shipping alone , daylight robbery I tell you! But I can get an interface like we are talking about here shipped to the UK free?

The pins probably don't match up directly to your pro mini, but the below serial converter module is very inexpensive and easy to modify to even be able to activate the auto-reset function if you wish. Note the bottom right hand picture, it shows solder pads for the typical serial control signals. Just wire a small .1mfd from the DTR pad to the base of the pin labled RST. Then cut the trace on the PCB that is going to that same RST pin. Now all you have to do is wire the ground, TXD, RCD, RST to the approprate connections to your pro mini board and you should be good to go. You can even power your pro mini via this USB module by wiring the +5vdc pin to your board.


Awesome :slight_smile:

What do you mean by .1mfd? I have no idea hehe.

I'm not sure which one is the bottom right on your screen since I'm using a tiny 1024x768 screen but I assume you mean this one:

I've attached what I can guess , Usually standards for live/gnd in UK is red and black respectively. Is that maintained in US circuitry?

Is Vcc the live wire here mabey?



Need to connect up power too. programmed 5V to Promini VCC

0.1uFd cap (also referred to as 100 nF)
I think Promini already has a cap between its DTR pin and reset pin.
Check the promini schematic on the Arduino Harware page.

Thanks CrossRoads :slight_smile:

I thought thats what lefty meant by 0.1uFd , it was the d that threw me XD

So I give 5V to the Vcc Pin.

Heres the schematics for the arduino pro mini:

There is a cap on the DTR pin , 0.1nF

I also see in the schematics the black is a GND and the green is DTR.

Where does the RST one go to? I take it this one is the DTR?

Prolific RST (now rewired as DTR) goes to Promini DTR pin (labeled GRN and connected to left side of C2)

Ok , cool , so its like this then? (attached)

Just trying to make it simpler for other noobs like me :slight_smile:


Wow , that pic uploaded pretty nastily...



EDIT: that went well...

Uploaded to imageshack , working there:

Pic might go better if cropped/resized to finish up around 800x600.

Awesome! :slight_smile:

Thanks for your help guys :smiley:

Now we play the waiting game for the adaptor to arrive... fingers are crossed heh


I finally came! Happy Days!

Shall try the method outlined here tonight...

EDIT: Whoopsy daisy , I meant It came lol

Ok so I kinda got it going. Snipped the trace on the board then soldered up a pseudo header very badly and , when I chonnected it up , the light on the arduino came on solid , the green one flashing , a good sign methinks! however , the connection is so bad I cant do anything lol.

I have ordered a breadboard and header pins lol

Spent some time tidying up my novice soldering and got the arduino to come on! IT'S ALIVE! I tried to upload the blink test and got out of sync error. The red light was on but there was a green one that seemed to have a loose connection , most likely on my board, but when i move the arduino on my homemade headers (made of an untwisted spring lol) , it will come on and off as I move it. I got it to stay in place and the green light was flashing quickly. I tried to transfer the sketch then but I dont think it worked. Either way , I stuck a green led accross port 13 and gnd and it flashed in some cases so can I assume it is working and to ignore the out of sync or is it just a feature of the board to send a clock signal over 13 , kind of like the other green flasing led next to the reset button?

EDIT: I did also notice in device manager , the yellow exclamation mark was showing , the one when it couldn't find any drivers for the device. Could that be it maybe?

Managed to get it "working" on the breadboard using some header pins. Now the red light always shows but the green one doesn't. The arduino is solid on the terminals so it can't be a dodgy connection. I've not bricked it have I? I managed to get it to do the blink test as I was saying so I don't think it is dead but I still get the "out of sync" error. Is this the real life or is it just fantasy?


First of all i would fix the driver problem.
You can do a search for cp2102 drivers, this came up fx.:

When your driver is OK you could try the Loop-back-test,73748.0.html

If this is OK, you know that your device is working

And just a note: the connections atleast on my cp2102 is: tx->tx rx-->rx

If all this is OK try uploading to the Arduino, and if it fails, try pressing reset when the message : Sketch size ... appear in the serial monitor

I have tried those drivers too but had the same issue. I have now soldered header pins accross the arduino's connection ports and can get a good connection using this but it is still giving the out of sync error. Glossing over the error , I powered up the arduino just to see if it uploaded but it didn't run the test I uploaded (blink test) I think the pin on 13 is synced up with the green LED on the board and that was flashing along with the LED I connected to it.

Looks like the green LED on the board is connected to pin 13 already which may say that the sketch uploaded , however , I tried changing it to pin 9 but the LED wouldn't flash. Green LED was still flashing though.

Did you try the loop-back test ?