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Topic: ATMega 328P-PU on Breadboard with PL2303 USB>Serial (Read 45511 times) previous topic - next topic


So, I've got a brand new 328P-PU running on a mini breadboard. I've successfully burnt the 16Mhz Arduino bootloader and I've managed to upload the Blink sketch fine by doing the manual reset.

I'm using a Prolific PL2303 based USB>Serial board and it has only 3v3, Vcc, RX, TX, Gnd connections. On an FTDI breakout, like the sparkfun you'd take the DTR line to Reset via a 0.1uF cap.

So...is it possible to get auto reset at all with my USB>Serial or am I stuck with manually reset for uploading sketches?


"Prolific PL2303 based USB>Serial board ... has only 3v3, Vcc, RX, TX, Gnd connections"

Does the PL2303 have a DTR, RST, anything you can break out to a pin to drive a capacitor for a DTR signal?   Many CP2102 boards do.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


Does the PL2303 have a DTR, RST, anything you can break out to a pin to drive a capacitor for a DTR signal?   Many CP2102 boards do.

DOH!!! I really should have thought of that one myself shouldn't I?

The Data Sheet shows Pin 2 as DTR_N. Looks like I might have to try my first bit of hand soldering to a SMD.


Use some flux, don't overdo it with solder.  Good luck!
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


hi & good day to you tack,

ive got good news for you !

its definitely possible to get the PL2303 Module you have to get setup for Auto-Reset as i have made a whole bunch of them for a few buddies but ended up modifying about 40 of them in total lol !

Your right from looking in the PL2303 datasheet, Pin 2 on the SMD chip is the one responsible for the Auto-Reset signal and its not connected to anything on that board so you got two choices here:
either get hold of a CP2102 which has an easily solder-able DTR pin or try modding the PL2303 adapter you already have like mine !

Here's a bunch of photo's taken of my modified one, this one was the prototype and soldering it was pretty easu but tedious and took a while just getting it right but after the many DAYS/HOURS of finding a method that worked i can hopefully save you some trouble if your looking to do the mod yourself !

The trick is to always use flux, as Guru crossroads said, dont overdo it and here's my method that worked for me:

Tin the tip of your fav soldering tip a little, only enough to cover 2 (TWO) pins of the SMD PL2302 !!!

Yup you read that right, TWO Pins, lol !

What i found out by Days of trying NOT to get solder on two pins was that it is actually easier to take solder AWAY from & UNBRIDGE two SMD pins than it is to only solder one-pin !



1 x 1 Male Pin Header
1 x 0.1uF Capacitor (100nF)


Get your 0.1uF Capacitor and trim the leads like so:
Pic 1

2. Get a fine file and gently shave down the back-side of the capacitor so that it sits right on the PL2303 chip, trust me, this works well lol !

Pic 2

Now these next photo's are from my really basic and cheap USB Microscope so the quality is not great but if you view these photo's in a small window (save to desktop etc !) then you will be able to see them better !

Place the Capacitor in top of the PL2303 Chip with the short leg bent onto the top of Pin-2 and you might want to literally add a TINY amount of super-glue to the back shaved-down side of the capacitor so that it doesnt move when your soldering, but i mean the SMALLEST amount, just enough to 'Tack it down temporarily' !

Pic 3

Apply Flux to Pin-1, Pin-2 & the Short Capacitor Leg, Tin your iron's tip with just enough solder to cover both Pins 1, 2 & the capacitor leg:

Pic 4

Pic 5

Now here's the trick !

As i found out, its imperitively much easier to bit-by-bit REMOVE solder from these two BREDGED SMD Pins by 1st getting rid of all the solder from the iron's tip, dipping the tip into some flux, i use a grease-like flux, NOT rosin-based, and remove the tip from dipping it in the flux quickly so that a drop of flux stays on the tip, touch the tip onto Pins 1 & 2 of the PL2303 chip and little-by-little remove the excess solder until the solder is only covering Pin 2 and the capacitor leg !!!

Heres a few pics in succession:

Pic 6

Pic 7

Pic 8

Pic 9

And then solder the 1 Male Pin-Header to the other side of the Capacitor and bend it so that it lines up with all the other pins of the module and tack it down with some more superglue OR get a hot-melt glue-gun involved, its not pretty but it will work b-e-a-utifully always AutoUploading sketches !!

btw i used a mold i had made to encase the module in casting resin and then sanded & polished it !

here's a few more pics !

PL2303 Modded:

PL2303 Mass-Modding, lol:

PL2303 Mass-Modding, lol (2):

The Finished Articles:

if anything isnt clear or you want me to explain anything just let me know & i'll be happy to help out !

have fun !
Si Vis Pacem, Para bellum
 ~  Publius Flavius Vegetius Renatus's


Good job. But maybe for your next batch purchase or for readers of this thread you might consider using those Asian based CP2102 USB serial TTL converter modules where they already breakout the control signals to unused solder pads, making the auto reset conversion a breeze, just cut the existing trace going to the reset pin on the output connector pin and then either solder a wire or a .1ufd series cap (depending if your 'target' board has a series cap already or not) from the DTR signal pad to the base of the reset pin on the output connector.




hahaha !!  :D  :D  :D  Absolutely Right @ RetroLefty !!  :D  :D  :D

Wouldnt ya know it, at the time i made these modded PL2303's i was completely oblivious to the CP2102 USB adapters and soooooooooo-WISH i would have known about them back then as it was alot of NECK-ACHE to tediously solder onto Pin 2 of the PL2303 chip - a serious amount of headache too lol  x 2 !!!

was indeed challenging to do but i think if i make anymore of these then ima definitely going to buy the CP2102 adapters and mod them easier lol !!

thanks so much for the heads-up too !!

why-o-why didnt i consult these forums back then lol ! well, some learn the hard (stupid!) way eh !!
Si Vis Pacem, Para bellum
 ~  Publius Flavius Vegetius Renatus's


offtherails2010, that is an awesome bit of how-to. Many thanks for that. I especially like the cast resin casings; very neat.

Thanks again for the time to post up with such a detailed explanation of modding. I'm sure it will save me a lot of swearing when I make my first attempt at soldering SMD.

On a nice note, a big package arrived full of Atmel samples today. Amazingly quick delivery from US to UK for free stuff! I only ordered on Thursday!


Your most-welcome tack !

i bought the resin from: (i'm also in the UK, London !)


and as i always buy stuff in bulk i bought the 5KG tub lol !

so plenty for other stuff i got plans for lol !

Also ive made a few instructables for Arduino on breadboards for beginners as im learning myself and got a terrible memory so its for future reference just in case i ever forget anything lol !

right here for Arduino UNO on breadboard

that ones jam-packed with info i found all over the net !

As a side note, ive been trying to request samples from Atmel for months but they wont send to me, all i keep getting is:

Your email domain is not authorized to request samples from Atmel.com.

Please use your company email domain to request samples

but my email address is a free one on yahoo and dont have any other email address, how did you get them to send to you, if you dont mind me asking ?!?  ;)

Si Vis Pacem, Para bellum
 ~  Publius Flavius Vegetius Renatus's

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