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[on:]

Hello,

I recently bought a usb ttl adapter which uses the cp2102 chip. I had some problems with autoreset when uploading a Sketch, and I found no clear description on how to get it working. To help other people, I wrote a small blog post which describes how to get autoreset working:

http://blog.tarn-vedra.de/2011/09/using-cp2102-on-arduino.html

Thanks.

[Reply #1 on:]

I think a cleaner and simpler solution is to just solder a .1ufd cap from the DTR pad to the base of the RST pin. Then turn the board over and cut the trace going to the RST pin. After that simple mod the RST pin can be wired to the processor's reset pin and the auto-reset function will work fine. I've done that mod and it works fine.

Lefty

[Reply #2 on:]

Lefty can you make a picture of your mod? Thanks!

[Reply #3 on:]

Kind of hard to get good pictures but here is what I have.

First shows wiring the .1ufd cap from the DTR pad to the RST edge connector pin.
Second shows other side of the board where the original RST signal trace is cut.

Lefty

[Reply #4 on:]

Thanks! Is it true that the tx and rx pins are reversed so you basically have to connect rx-rx and tx-tx..

[Reply #5 on:]

I have actually had the exact same issue but i never had a cap between the pad (cant remember the name) and the rst pin and cut the trace.

Here is the pinout I was using on the arduino Pro Mini which , I imagine , is the same setup.

http://img12.imageshack.us/img12/663/arduino2.jpg

It is interesting that you mention the cap because I was under the impression I wouldn't need one since there is already a 1mfd cap on the RST pin arduino side.Then again it could be the RST on the other side of the board I was seeing there...

[Reply #6 on:]

Have a look here if you want to have a butchers at my topic too:

http://arduino.cc/forum/index.php/topic,96697.msg746116.html#msg74611

[Reply #7 on:]

Another thing, if the arduino already has a cap on reset pin - I'm assuming that the arduino pro mini has one (I looked at the schematic), then I don't need to add that cap to the programmer? Or it doesn't matter if there are maybe 2 caps?

[Reply #8 on:]

There's a cap on the DTR pin on the arduino, which then connects to the reset pin.
Adding one to the CP2102 is not needed.
If you've built up your own arduino clone with no cap, then a cap on the programmer is a good idea.
Not sure if 2 in a row will work as intended - altho mathematically the resulting capacitance value is (C1*C2)/(C1+C2).
So two 0.1uS = 0.05uF, may go low long enough for a successful reset, or it may not.

[Reply #9 on:]

Another thing, if the arduino already has a cap on reset pin - I'm assuming that the arduino pro mini has one (I looked at the schematic), then I don't need to add that cap to the programmer? Or it doesn't matter if there are maybe 2 caps?

You DON'T want ANY capacitor between reset and ground!  If the "arduino" has such a capacitor REMOVE IT!  The capacitor is connected in SERIES between DTR and the processor reset pin.  The processor should have a 10K resistor from reset to VCC.  A .1uf (100nf) capacitor will provide the correct timing of the reset pulse on a 5v circuit.  A 3.3 volt circuit might need a larger capacitor.  The value shouldn't be critical however.

[Reply #10 on:]

Calm down there scharkalvin! The arduino's have 0.1uF cap between the DTR pin and the reset pin, not from reset to gnd.
Of course, reset to gnd would just drag any reset pulse out as it charged up and came out of reset.