Adding Auto-Reset Pin to PL2303 Based Serial-USB Modules

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About: Mechatronics Engineer . Hopeless Realist

I got a couple of cheap PL2303 based Serial to USB modules off AliExpress thinking they would work for uploading code on to my Arduino Pro Mini. Unfortunately, I later figured the modules didn't have a reset pin and everyone who's tried manual reset, knows it's a pain.

A quick look into the 2303 datasheet confirmed that the chip does have a pin dedicated for auto-reset and that it wasn't connected to anything on my modules. I gave it a try, pulling out the pin through a small capacitor and it worked!

Although, most of you hackers out there are more intimidated by SMD chips than a Trex running at you, this hack is rather easy, really.

Things you'll need:

  1. 47nF ceramic capacitor
  2. A hookup wire with a male/female header
  3. Micro solder iron
  4. Flux
  5. Desoldering wick
  6. Magnifying glass (optional)
  7. Heat shrink tube

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Step 1: Prep the Parts

Fortunately, my modules came with a SSOP28 package, I'd be damned if it were a QNF.

Rip the heat shrink if it came shrunk and locate Pin2 on the chip.

Take a 47nF ceramic capacitor, cut and bend one of its legs into a U-shape such that when the pin is soldered, the cap sits on the bottom side (or you can solder that cap in whatever way that pleases you).

Step 2: Set It Up

I used my helping hand to precisely align the capacitor leg on to Pin2 and then dab some flux on the pins before I soldered it. Don't really need a 3rd hand I guess, I used it because I don't have a steady enough hand for the job.

Step 3: Soldering

Gotta be a bit careful on this step, clean the solder tip, dip it in flux, melt on a small amount of solder on to the tip, just enough to tack on the capacitor to Pin2 and use a magnifying glass to inspect the joint, in case you're paranoid of a solder bridge.

Keep some desoldering wick on hand just in case you accidentally bridge the adjacent pins. I needed the wick thrice on hacking two modules.

On the flip-side, solder a small piece of wire with a male/female header on to the capacitor's free end and be sure to insulate it.

Step 4: Testing and Finishing Up

Hook up the module to a Pro Mini and upload the infamous Blink (or any other code!) to confirm that your module is working.

Finish off the hack with some nice heat shrink. I love them clear shrinks!

5 People Made This Project!

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5 Discussions

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arnablue

1 year ago

Many Thanks for the Pin instruction. I had this Problem.

Now, I did some upgrade to mine. I used the "3.3V pin" (useless for me) as "DTR pin".

No extra capacitor or hanging wires... Details in Pictures...

IMG_21.jpgIMG_20.jpg
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neurino

1 year ago

Watch out the chip, mine had a CH340G which has DTR on pin 13

6540D95D-ABBA-4D39-B08C-D280AC8860FB.jpeg
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AbhishekD113

2 years ago

Awesome hack !! :)
just would like to know, if i skip the capacitor and directly connect the pin would it be ok ?

Thanks.

-Regards,

Abhi

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xmontik

3 years ago

Hello, please what type of programmer have I set in arduino IDE, to get pl2303 work as programmer??

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Parky1972

4 years ago

Yep!
I managed to convert mine just as described.
So thanks for that as trying to time pressing tge reset button was becoming tiresome!!

Thanks.