Introduction: Arduino USB

LOG: Made a correction/modification Step 3 and added a picture step 5.

So many Arduino users have RBBBs(Really Bare Bones Board (Arduino))  or Anarduinos or Boarduinos that could use a USB interface to program and power them but don’t want to spend $15-20 for a USB BUB or FTDI cable. This Lazy Old Geek is one of them.

 Theory: Most Arduino clones are programmed with a PC using a USB port. Theoretically, they could be programmed with an RS232 port but it is really hard to find a PC with RS232. Some Arduino clones come with a USB converter but most do not. Most require a TTL serial connection. TTL stands for Transistor-transistor-logic which basically means 0-5Vdc logic. So these Arduinos require a USB to TTL converter. One of the more common is the USB-BUB by Modern Devices:

I own one and like it but they’re costly.

 So I saw these (see picture) USB to RS232 Serial DB9 Adapter cables on ebay for less than $2 so I bought one. Since I had three weeks to wait for it, I thought about and realized that it probably wouldn’t work as true RS232 has plus and minus 3-15 Vdc signals. The Arduino requires TTL levels which are 0 and 5 Vdc. Nevertheless, I’d already bought it so I took it apart. It apparently had a PL2303 chip in it and I saw no level converters. Anyway, I don’t have any kind of RS232 device to check it with but don’t see how it could ever work with a true RS232. But the other thing is; I couldn’t get it to work with an Arduino. If anyone has gotten one of these to work, please let me know how.

 Next I saw this article about converting a camera adapter to work with an Arduino.

You might be able to get these adapters cheaper than the one I used. Following the guidelines it should work fine.

Step 1: My Arduino USB

I bought this PL2303 adapter on

USB2.0 to RS232 TTL Converter Module PL2303 +4pcs cable

But they can also be bought directly from Virtual Village

for $2.99 plus $0.99 postage and handling. I’ve had good luck with Virtual Village.

Well made board, works with TTL.
LEDs for power, TX and Rx

No schematic, operating instructions
Uses a standard USB connector instead of a mini.

Other parts needed:
2- 6 pin female headers

Optional parts for auto reset:
1 capacitor 0.1uFd (104)
1 male header pin
Wire wrap wire or magnetic wire.

Total cost should be less than $5.

Step 2: Functional Test

So let’s see if the adapter works. If you look at the picture, you’ll see a two pin jumper on the outer, lower two pins. There is no documentation but this appears to be a loopback jumper. It connects TX to RX so anything sent out is fed right back in so leave it on for now.

 Plug it into a USB port on your computer. You should here a kerchunk on your speaker and the red LED on the adapter should light up. Now my Microsoft Vista machines automatically found the PL2303HX drivers but if you need to find them, they are here:
Prolific is the company that makes the PL2303HX used by this adapter. (TW stands for Taiwan). Find the driver for your operating system and install it.

 I am assuming that you have Arduino software installed. Open it up. Click on <Tools><Serial Port> and select the correct COM number for the PL2303HX.

If you have several Com ports listed and don’t know which one then you need to go into Device Manager. For my PC with MS Vista, I do the following:

Click on the little Start icon, lower left corner
Right click on the <Computer> icon
Select <Properties>
Click on <Device Manager>
Click on <Continue>
Next to the <Ports (COM&LPT)> icon, click on the <+>
The drop down should show <Prolific USB-to-Serial Comm Port (Com4)
Or something similar. The Com port is the number.

Go back to the Arduino software and select the correct Com port number.

On the Arduino screen select the far right icon <Serial Monitor> or press <Ctrl><Shift><m> at the same time.

A serial monitor window should open up. Type something into the text box. Hit <Enter>. The typed text should jump down into the second text box. That means the text is going out the TX pin, into the jumper and back into the RX pin.
The adapter is working correctly. Remove the jumper.

Step 3: Decision Time: Auto Reset or Not

When you send a sketch to the Arduino, it will briefly pull a serial pin called DTR low which will reset the Arduino. This can be done manually by pressing the Arduino reset button for a few seconds after sending the sketch. Timing this correctly is a little tricky but can be done successfully with some practice.

 Now this adapter doesn’t use the DTR pin, so it has to be modified to be able to use it. This requires some good soldering skills that you have to decide if you have. I was able to do it and I’m old. But it wasn’t easy. If you want to skip the Auto Reset and do the Reset manually, skip the rest of this step.

 Okay you have to solder a wire to one (and only one) pin on the PL2303 chip. The pins are 0.025 inches (0.65mm) apart. That’s not very much. A wire needs to be attached to pin 2 (DTR_N). But it can easily be shorted to pin 1 or 3 so be careful. Here’s what I did.

 My soldering iron had a plain copper tip. I sharpened it to a point. I put a cutoff wheel in my drill press to do this. By the way, I did the same thing to my DMM probes. You can also do it with a file. Plug in the soldering iron and tin the tip.  

 The wire I used is 30AWG wire wrap wire. I know others have used magnetic wire but I don’t have any or know where to get it cheaply. I happened to have some wire wrap wire but it can be purchased at Radio Shack or ebay.

Slightly irrelevant information:The little tool I have is a great way for stripping off insulation of wire wrap wire. You just slip it into the notch in the middle of the tool, pull it down into the V and pull the wire out. Unfortunately, I priced these tools new and they’re about $25-$30. Outrageous.

Okay, so using reading glasses, a magnifying glass and a bright lamp and a little solder, I was able to get it soldered. See picture. Note the little circle on the PL2303Hx chip that indicates pin 1 and that the wire is soldered to pin 2.

If you have a DMM with sharpened probes, make sure that the wire is electrically connected to pin 2 and not to pin 1 or pin 3.

Next, I hot glued the wire to the adapter PCB. It actually covered up D3 the LED for TXD but it’s clear and the light shines through it. See picture.

I hot glued a 0.1uFd capacitor (104) to the top of the PL2303HX chip and soldered the other end of the wire to one side of the cap.

The other end of the cap goes to the Arduino reset pin but I decided to put it on a header pin so that I can make jumper cables for it.

I snipped off a single male header pin and soldered some wire wrap wire to the short side and clipped it short as much as I could. See picture.

Then I stuck the single pin into a female header. See picture. Actually, I have some 50 pin headers but only needed six pins. To trim this, what I do is go to the pin past the ones you need (in this case the seventh). Take a utility knife or Xacto and scored in the middle of where the pin runs. Do both sides a couple of times. Then carefully bend the header until it breaks apart. You will have an extra metal contact to toss or recycle.

 On the adapter, there is a five pin strip of male pins labeled TTL. I put the female header on the strip so that the extra pin was just past the pin labeled 3.3V.

Caution: Though the PCB is coated, the clipped off solder connection can be sharp and penetrate the coating. This happened to me on another of these so I had to stick a piece of tape under it to insulate it.
Now the insulation on this pin sticks up a little higher than the other five pins because of the wire and solder. But this is okay. The PCB is coated. Then I hot glued the DTR pin to the PCB.

Then I soldered the other end of the wire wrap wire to the capacitor. See second drawing.

Step 4: Wiring It Up

Many Arduinos like the Anarduino, RBBB and Boarduino have a USB connector with six pins configured as Gnd, Gnd, 5V, Tx, Rx, DTR. So I decided to make a six pin female to six pin female adapter cable to go between my adapter and my Arduinos.

TIP: I have a USB BUB and use it on Anarduinos and RBBBs. They look quite differently and it is easy to put the USB BUB on opposite from what it should be. I have done this several times. I’ve been lucky that I haven’t had any apparent damage. To help prevent this I borrowed some nail polish and painted the DTR side red on both the USB BUB and the Arduinos. Now I just have to match the reds so that I don't put it on reversed. See picture.

Notice that for the six pin female header in the picture, I cut a little notch out of one pin. This is so it will fit better on the DTR pin which is sticking up a little bit. This will also identify which of the headers goes onto the adapter since they’re both six pin. I also plan to borrow a different color nail polish for this DTR pin. (see picture)

NC means no connection
Like pins connect to each other, e.g. Tx to Tx
My adapter header has the notch for the DTR pin .

Decisions: If you decided not to use DTR then you connect the following:

Adapter         Arduino
NC                  NC
NC                  Rx
Gnd                Tx
Rx                   5V
Tx                    NC
5V                   Gnd
Just four wires. If you don’t need 5V from USB to power the Arduino, then skip the 5V also.

If you have DTR wired up then connect the following:

Adapter         Arduino
DTR                DTR
NC                  Rx
Gnd                Tx
Rx                   5V
Tx                    NC
5V                   Gnd

The Anarduino has a ground connected to two pins of the serial male header strip. Apparently, so does the Boarduino. If you are using one of these, then the following cable won’t work and can easily damage the USB adapter chip. I modified my Anarduinos so that this will work. The RBBBs are okay.

Now, my cable will be a little different as I have RBBBs and I modified all of my Anarduinos so that they can accept 3.3V on the second ‘Ground’ pin. This is a jumper option of the USB BUB. Since most of my sketches use 3.3V to set Aref, I will wire it up in my cable.

Caution: If you do use this 3.3V be careful as it isn’t clear (to me anyway) how much current the chip can supply. The PL2303HX has a 5V to 3.3V converter in it, but this 3.3V is also the main power supply for the rest of the PL2303HX. In my designs, I use 3.3 for Aref. It is drawing less than 0.1 mA so shouldn’t be a problem.

Adapter         Arduino
DTR                DTR
3.3V                Rx
Gnd                Tx
Rx                   5V
Tx                    3.3V
5V                   Gnd

 For this cable, I made the wires 5” long. Note that I used heavy wire for the Ground and 5V and used wire wrap wire for the other signals. The 5V and Ground will need to carry a little more current. Plus this adds a little strength to the cable. I wrapped some electrical tape on both headers as additional strain relief.

My adapter works great!

One of the advantages of using a cable is that you can make several different ones. You might want a short one or in my case, I might want one without the 3.3V. If you make several, you might want to label them.

Step 5: More Info and Conclusions

Level Translation:
If you read the article about the other adapter I referenced, he talked about Level Translation. He is basically correct. The signals coming out of this adapter are 3.3V and will work with Arduinos.

For the one signal, Rx coming from the Arduino, I ‘reverse engineered’ the adapter circuitry. They have a resistor and diode in the circuit that will limit it to 4V. Plus the PL2303HX documentation does say that it is 5V tolerant. Plus on the adapter, the five pin connector says "TTL' which means 0-5V. For all of these reasons, I didn’t feel the need for a voltage divider.

For all of you electronic circuitry geeks: If you look at the schematic for the Anarduino, Boarduino and RBBB, the DTR (sometimes identified as RTS pin) going to the USB connector has a 0.1uFd capacitor before it’s connected to the Reset pin on the AtMega. And further perusal of the USB-BUB schematic and my adapter shows another 0.1uFd capacitor from the DTR pin of the converter IC to the connector. So there are actually two 0.1uFd capacitors in series.

So what does that mean? Well, many of you know that if you connect two resistors in series, the resistances add. Two capacitors in series are different. The actual formula to find the capacitance is C1*C2/(C1+C2). So the equivalent capacitance is 0.05uFd.

So other geeks may be wondering what is a capacitor doing in the middle of digital circuitry? Here is basically what happens. When the USB is ready to operate, it sets DTR low. This low signal is passed through the capacitors and pulls the Reset* pin on the AtMega low for a short period of time. This resets the AtMega. The capacitors will start to charge up so the AtMega side will go back to 5V and the AtMega will resume operation.

Caution: I noticed that the PL2303 adapter that I received is slight different from the adapter in the picture from Virtual Village. I hope that mine is the current version and that they are no longer selling the other version. But if you do get one of these and it’s different you may have to wire it differently.

This adapter also comes with four piece cable. If you are not using auto reset and/or have extras, you can use these instead of making a cable like I did.

There are several other versions of PL2303 adapters. Some of them have the DTR pin connected so that you wouldn't have to do the modification I did. However, the one I saw was a lot more expensive.

Conclusion: Well, I hope this helps some of you save some money.

The last picture is an adapter cable I finished with something called cable lacing.

This was done with some waxed dental floss that I got as a sample from my dentist. I don't really have the a very good technique so won't go into details but if your interested, just do a search on 'cable lacing.'


westfw made it!(author)2011-06-16

You probably couldn't get your first USB/Serial converter to work because it was providing (somehow) INVERTED TTL serial traffic. Inverted TTL will drive most devices that expect to talk to real rs232 devices, but not to devices like Arudino that want to talk non-inverted TTL...

An extra level of inversion might fix it.

Pete+Kirkham made it!(author)2012-02-12

I have used them with an extra TTL inverter.

davidp680 made it!(author)2016-11-23

Excellent! I found an old SN74LS04N, powered that from the Mini, fed TXD through one gate, RXD back through another and, instantly, the USB serial connector works. A eureka moment.

I was just about to resort to a convertor module. Many thanks.

msuzuki777 made it!(author)2016-11-23

Great job!


motiQ made it!(author)2015-10-10

Help Me........

I tried to make the DTR pin from the second pin of the ic. But..... I don't Know What was happened, The Blue Led of Pl2303 is still lighting when connect to pc

Before soldering that didn't happen........

msuzuki777 made it!(author)2015-10-10

I'm not sure what happened but most likely you shorted pin 2 with another pin with solder. I have a really hard time doing this modification any more. What I've been doing is taking an exacto knife and while heating pin 2 with a soldering iron, lifting the pin away from the pad. When it's sticking away away from the PL2303, it's a little easier to solder to without getting a solder short to other pins.

Actually, right now, I stopped buying PL2303s and started buying and using CP2102s. The ones I get already have DTR connected to a pin.

Good luck.


SuperTech-IT made it!(author)2014-10-17

So - best case scenario, I'm on my own.

Worst case scenario, I'm screwed.

Thanks! LOL!!! Well, I'll mimic the ChipKit UNO32 board with an FT232RQ and hop to heck it works then I guess. The MPIDE just isn't manually triggering the DTR when it goes to program the PIC the way it does when if goes to program an Arduino...and unfortunately, I want to add USB to both of my UNO eliminator boards for my RGB LED cubes (which you can see in my instructables here).

msuzuki777 made it!(author)2014-10-18

Yes, but are you sure the MPIDE is supposed to trigger DTR? If the PL2302 works with Arduino then it's most likely the hardware is working and I would guess the MPIDE does not use DTR. The Arduino environment only uses DTR to reset the ATmega so once a program is loaded, it starts running it.

(The older Arduinos used CTS instead of DTR)


SuperTech-IT made it!(author)2014-10-18

MPIDE triggers the DTR when programming an ATmega328P (Arduino) but not when programming the PIC.

I also have a cap on the CTS, so either method should work. Just with this USB2serial chip it's not.

SuperTech-IT made it!(author)2014-10-17

OK, I just found out that one of my issues if I am not uploading to an Arduino. The DTR does change when I use the Arduino IDE - but sits there looking stupid when I try to upload to the PIC32 using MPIDE. This could be a bit of a noodle scratcher.

msuzuki777 made it!(author)2014-10-17

Can't help you there as one of the reasons I chose the Arduino was so I wouldn't have to figure out PICs.


SuperTech-IT made it!(author)2014-10-17

I may have to switch to the PL2302. I just tried this with cp2102 which is supposed to be an equivalent type chip (but nice and small and square) and no-go.

The logic analyzer doesn't even see a DTR logic shift when it goes to send data.

I might try the FT232RQ next, but this means fabricating new boards. UGH.

(and no, I didn't make a mistake with the caps...LOL...I dunno how I got that backwards in my mind...chalk it up to a brain fart I guess)

msuzuki777 made it!(author)2014-10-17

I think I have used the CP2102 with Arduino but decided not to use it as I have a lot of PL2302s and didn't want to get confused with different cables and drivers.

SuperTech-IT made it!(author)2014-10-17

.1uF is 103, not 104 which is .01uF

msuzuki777 made it!(author)2014-10-17

Not according to all the tables I've seen.


SuperTech-IT made it!(author)2014-10-17

Please dxcuse my eyslexia.
I even back talkwards sometimes! LOL!

msuzuki777 made it!(author)2014-10-17

Not a problem. I have to look it up every time I use it.

marlarius made it!(author)2014-08-05

Thanks for this great tutorial!

I guess this would work for programming an Attiny85 as well, but how should the connections be in that case?

msuzuki777 made it!(author)2014-08-05

If I remember correctly, the Attiny85 does not have serial pins so cannot be connected directly to this Arduino USB. You would have to have an adapter like a regular Arduino to program the Attiny.


marlarius made it!(author)2014-08-05

Thanks for quick reply!

I already use my Arduino to program Attiny85 as described here:

I just though that instead of using Arduino pin 10-13 to connect to the attiny, it would be possible to connect the relevant pins from the USB-to-TTL converter, just like you do here for the Atmega.

After all, my USB-to-TTL converter looks much like this AVR programmer except for the socket.

msuzuki777 made it!(author)2014-08-05

Ok, here's the problem I see. Pins 10-13 of the Arduino are used as SPI, Serial Peripheral Interface, and this is what is used to communicate with the Attiny85. The Sparkfun product uses an Attiny84 to generate an SPI to communicate with the Attiny85.

But the Arduino USB generates an RS232 connection. While this is also a serial connection, it is not the same as SPI. (For one thing, it does not have a clock line. sck. Another problem is that RS232 is asynchronous while SPI is synchronous) so I don't think the Arduino USB can be connected directly to an Attiny85 to program it.

But I'm no expert on programming Attiny85s so there may be a way to do it.


marlarius made it!(author)2014-08-07

So it is a bit more complicated than I first thought. I will just stick to programming it with my old trusty Arduino. Thanks for your explaining me all this.

goldenshuttle made it!(author)2014-05-14

it is a great Instructable...But perhaps you created some the text you mentioned that one side of capacitor goes on pin 2 of PL2303 and the other side goes to RESET pin of the pics, you seem to connect capacitor to DTR not RESET...which one is it actually ? there is a conflict between the text and the foto's my friend...

msuzuki777 made it!(author)2014-05-14

Yes, this is rather confusing. However, the DTR from the PL2303 doesn't connect directly to the RBBB Arduino reset pin. It connects to a capacitor that is connected to the reset pin. On the RBBB PC board, this connector pin is not identified. On the RBBB schematic that I have, it is identified as RTS#.

But you are correct. There is no DTR pin or signal on the RBBB. But I wouldn't call it the reset signal either. Maybe it should be called C4?

(By the way, I believe in the past, the serial RTS signal was used to reset the Arduino instead of the DTR signal. That is why the RBBB schematic identifies it as RTS.)


goldenshuttle made it!(author)2014-05-15

Thanks for replying. On my Arduino pro mini there is a DTR and also there is a RESET. To which one should I connect the other side of the 104 capacitor ?

msuzuki777 made it!(author)2014-05-15

I didn't know the pro mini had a DTR pin. I would connect the 104 cap to the DTR pin.


alahamm made it!(author)2013-06-10

Shouldn´t this adapter be connected to an Arduino to run Serial Monitor?
Anyway to test it without a serial Device? Thanks.

msuzuki777 made it!(author)2013-06-10

This simple test is just to test that the PL2303 driver works and that the basic module is working. Though the Serial Monitor is part of the Arduino environment, it doesn't really require an Arduino to use it.
Later in the Instructable, you can test it with an Arduino.


nodoubtman made it!(author)2012-12-29

Hi! I have the same type of adapter, i'm wondering if i can upload sketch with this adapter?

thank you!

msuzuki777 made it!(author)2013-01-02

If you follow all of this Instructable, you should be able to upload sketches. I use these adapters to upload sketches all the time.


ahmad2370 made it!(author)2013-01-02

how to burn Arduino bootloader to a fresh ATMEGA328???

msuzuki777 made it!(author)2013-01-02

Please see this Instructable:


weish made it!(author)2012-07-09

this cable design of yours is ingenious. is it possible to use this setup to burn a bootloader on a fresh chip, simmilar to using an adafruit FTDI friend as an AVR programmer? i've been pricing out building myself an arduino from scratch, and at this point the FTDI friend is the most expensive part i need (half my costs, actually)

msuzuki777 made it!(author)2012-07-09

I never heard of FTDI Friend until now so I did some research.
So my answer is 'I don't know.'

But I do have an opinion. It appears that this method requires some thing called the Arvdude bitbanger and what I have found is that this was written specifically for the FT232 chip which is not what my adapter uses.
So you might try it anyway, but I would guess it's not going to work.

I wrote an Instructable for burning bootloader that is pretty cheap:

I agree with you that the FTDI adapter is very expensive and I only have one, a USB-BUB,.

Suggestion: Unless you are an experienced microcomputer user, I would suggest you buy a complete kit, like a RBBB or at least a bootloaded Atmega328 and build a working Arduino clone. Here's one of mine:

With a working Arduino-clone, it's a lot easier to get started.


pfred2 made it!(author)2012-07-14

I'm struggling over here trying to understand what you mean when you say, "So you might try it anyway, but I would guess it's not going to work"

Can you please tell me what is not going to work when they try what? I'd like to try something similar to what is described in this article but if it isn't going to work then perhaps I am better off not doing it.

Anyhow thanks in advance for any light you can shed on this mystery. If it turns out to be what I think it is I have a guess why it may not work? As of now I'm not entirely sure what it is though. I think I know, but I'd just like to be positive.

offtherails2010 made it!(author)2012-05-22

Hello & good day to you Lazy Old Geek (love the nickname, lol x 2!!!)

Befor i start with my question, A 'MAJOR' Thanks for making and sharing this instructable with us all, its an amazing piece of very-well-laid-out instructions that even an electronics learner like me can follow!!

Have already rated it 5 stars - Many thanks !!!

 Ive also acquired the same PL2303HX usb TTL converter from HERE (very very low price so i ordered 3 just in case i mess this up!)

Anyhoo, ive installed the driver for it and my windows 7 pro has accepted it perfectly but my system wont instal the RBBB which i bought 3 kits of direct from Modern Device but cant get it installed on my pc because i have no driver for it.

This is what ive tried so far:

- Driver from the website (the driver that came with Arduino IDE)
- FTDI Drivers ? (i read somewhere that these were needed but not sure now?)
- Google searched my brains-out for an RBBB Driver but still unable to find one after 2 weeks of searching ?

None of this worked (by manually selecting the driver to be updated by device-manager - update device properties etc)

Please please please could you say where you found the driver for your RBBB Arduino clone recognised ?!!!?

i have 3 of these RBBB's all working and soldered together and the pilot light comes on as it should in the instructions of soldering these boards together but i do not have 'Arduino Uno' in my com ports in device manager, just an 'unknown device' (which is no doubt my 1st RBBB clone!)

I really want to do this instructable as its the most-in-depth article online - EVER !!!!

Many thanks once again for the push in the right direction and once again MAJOR thanks for publishing this truly amazing, well thought-out & extremely inspiring piece of ingenuity !!!

msuzuki777 made it!(author)2012-05-22


I am assuming you are rather new to the Arduino world.

Most Arduino users communicate with Arduinos and clones like the RBBB using an old PC communications protocol called RS232. Nowadays, most computers don’t have an RS232 port. These have been replaced by USB, which is another serial communications protocol.
The PL2303 device actually converts USB to RS232 (and back).

So the simple answer is that there are no drivers for the RBBB or any other Arduino. The RBBB is an Arduino clone.

But here's some tips for your setup.

Most all Arduino users use the Arduino software downloadable from

This software will talk to any Arduino/clone using the RS232 protocol through the PL2303 device. You will want to download and extract this.

A good introduction to Arduino is this Instructable:

Once you download and install the Arduino software and run it, you need to setup a couple of things.
1. Connect an RBBB to your USB adapter and plug it into a USB connector. You should have an LED on your PL2303 device and one on the RBBB.

2. Start Arduino software. This is not very user friendly so you will have to find the Arduino application icon. Mine is under the Arduino-1.0.1 subdirectory. It’s probably a little green icon with a – and a + inside it.

3. Select , then
4. There should be a Com# with a check mark in it. Mine is COM3. This is where the PL2303 is connected.
5. Select , then
6. Click on This is what the RBBB emulates.

Now you should be able to load up Examples or other programs to your RBBB.

By the way, the FTDI drivers refer to the more common IC used to convert USB to RS232, the FTDI232 IC. Since you are using the PL2303, you won’t need this driver.

Hope this helps.


offtherails2010 made it!(author)2012-05-23

Hey many thanks for the cable lacing tip as well, i totally forgot to say thanks for that one !!!

Yup, you guessed it, ive only just started messing around with arduino's and have soldered 2 of them so far, but everytime i try to upload the simple 'Blink' sketch from the arduino IDE i get this message in red:

                  avrdude: stk500_getsync(): not in sync: resp=0x00

also apart from the red LED on the PL2303 being -on- constantly, there is another LED on the PCB, a Yellow LED but this doesn't switch on until i unplug my RBBB and there's no activity or change in the LED's as the IDE software tries to upload ? Would you know whats causing the sketches to fail ?

 I have been using instructions from HERE to upload, the manual reset way but after i stumbled upon your instructable i thought i'd rather have the software reset instead as its much less messing about with trying to find out how many seconds to hold down the reset tactile switch on my RBBB !!! plus i dont mind trying to solder a capacitor to the DTR pin on the PL2302 as i have two of these USB PCB's but they are so cheap it wont really matter if i screw it up !

So as soon as i can just figure out why i cant get a simple Blink sketch to upload, then i'll be soldering the PL2303 PCB as per your great instructable !

I really just want to see the sketch upload just for peace of mind that everything works as its supposed to (as standard, lol) and then modify the PL2303 after !

Please would you be able to say if you had the problem above?
ive trawled through the arduino forums and modern-device forums and still dont have an answer for this - its driving me crazy as ive 2 RBBB's fully soldered and awaiting sketches but still having this problem !!!

Please help if you can !

Many thanks in advance again LOG !

msuzuki777 made it!(author)2012-05-23

I’m fairly certain that Arduino failure code means that the computer is not connecting serially to the Arduino. I’m not sure if I can help or not but here’s some ideas.

First what I would do would try my functional test. I think it’s my step 2, but basically, you take the PL2303 module and connect Tx and Rx and make sure the module by itself is working. This one should work.
Second when you connect the PL2303 to the RBBB, make sure you have Gnd, +5V, Tx and Rx connected.
Third, I’ve tried that manual reset method and it’s pretty tricky. I think I’ve gotten it to work but the timing is really critical. I can’t remember but I think I may have had to wait up to 5-10 seconds.
Fourth, You might try swapping the Tx and Rx connections on one side. It’s somewhat confusing about which goes to which. Tx stands for Transmit and Rx means Receive but it depends on your point of view. Are you talking about the computer or the Arduino. Anyway, it shouldn’t hurt if you have it reversed but it might work.
Fifth, if you haven’t already try all your PL2303 modules and all of your RBBBs in different combinations.
Sixth, do you have an oscilloscope?
Seventh, you might try my reset mod anyway.

Do you have any friends into Arduinos? Maybe you could borrow a USB-BUB or adapter to test your RBBBs.

I am not sure if your PL2303 module will work with the Arduino. I’ve had some that I couldn’t get to work.

Good luck and let me know how it goes.


offtherails2010 made it!(author)2012-05-24

Hello & Good day to you L.O.G !!

Thank you very much for the extra support into the start to my arduino adventures !!

After re-reading your 'ible a few more times i had decided that things would just go much more smoothly if i just sent sketches to the RBBB via the DTR Automatic software reset method....

I also noticed that the PL2303 that i have is slightly different to the one in your 'ible and so hunted for the exact same version you have 'tinkered-with' lol, and have four of them on thier way, alot more expensive than the one i have, (pictures below) but im guessing that the pricipal of what we are trying to do is basically the same, it cost £2.78 & the one i bought cost £1.61 - both from ebay, but a darn sight cheaper than the FTDI or BUB/BUBII PCB's !

i  bought 4 of these PL2303 PCB'c for the price of one BUB II !!!

Sorry, back to the matter at hand, i soldered a 0.1uF Cap to Pin 2 of the DTR_N Pin of the chip on the PL2303 and soldered the other leg of the cap straight to a pin header and hot-glue-melted it into place so that was the most fiddly soldering ive ever done - ive usually steered away from any kind of SMD work/rework but this thankfully turned out ok!

Now before i connect it all up, i'm a little fuzzy on 'Step 4' - because i want to try to copy your great work 'to the letter' in the hope of eliminating any possible problems in regards to uploading sketches with the software reset !

Ive included a pic of my PL2303 ( also does the ATMEGA 328 Chip & ATMEGA 168 have any difference to the pinouts ??? because the RBBB instructions are still only showing the ATMEGA168)

I take it that the DTR pin from the PL2303 goes to the reset pin on the RBBB ? am i to assume correct ? Sorry for the silly question but ive read some right-horror stories on the arduino forums about frying the atmega chips and i only have two of these and would just like to be sure ?!!?

The only pin-outs i have on my PL2303 are:
DTR     (Newly created thanks to you!!!)
3v3      (3.5v {measured with DMM})
VCC    (5v)

so do i just connect it up as your instructions say, as: (for software reset?)
Adapter         Arduino
DTR                DTR (is this the reset pin on the RBBB ???)
NC                  Rx
Gnd                Tx
Rx                   5V
Tx                    NC
5V                   Gnd

Once again many thanks for the awesome help, i'm truly grateful for the time you have taken already to help me out!!!

msuzuki777 made it!(author)2012-05-24

The Atmega 328 and 168 do have the same pinouts. The only difference is internally, the 328 has more memory. One of the early official Arduinos used the 168, then latter converted to the 328. Many clones like the RBBB started with the 168 and later replaced it with the 328 but didn't bother to redo their documentation. In most cases, you can either type as long as you select the correct one in the Arduino software.

And yes, you are correct that the PL2303 DTR connects to the RBBB DTR pin which connects to the reset on the Atmega328. Actually, my documentation calls it RTS but for this application, it works. FYI, earlier in Arduino history, This was connected to the RTS to do the reset. I don't know if this still works.

By the way, your smd soldering is great, Much better than mine.

Let me know how it goes. As you get into Arduinos, it's nice to have lots of spare parts. One of my PL2303 modules died and I did lose an Atmega328.

By the way, I've had some problems with the header pins and female headers being intermittent. I buy the cheapest I can find so that's probably a factor. But actually one of my problems was with an 'expensive' USB-BUB.


offtherails2010 made it!(author)2012-05-24

!!!   ***   ***   *** LAZY OLD GEEK   ***   ***   ***   !!!

Your a GENIUS !!!

Thanks so much, i have a 'Blinking RBBB'  !!!!

If it wasn't for your great instructable i would have still been sitting here scratching the hell outta my head going crazy tring to figure out why i couldn't send sketches to my RBBB !!!

Ive got 2 RBBB's soldered together and another 2 needing to be soldered but i'll load 'Blink' onto all of them just to know that my soldering was done a-o-k !

Many thanks for the smd praise, its extremely appreciated, i'd been avoiding learning electronics for the past 15 years but now that we have toys like arduino's around i just had to start learning & ive only started this year so it really does me proud to hear such a comment from a professional electronics expert !

Here's What i Used:
*** THIS awesome instructable !!! ***
* This PL2303 TTL to RS232 USB Converter (Very Cheap!)
* Driver From This instructable !!! (STEP 2)
* Windows 7 64bit
* Arduino IDE (From
* 1 x 0.1uF Capacitor (100nF, mine was rated @ 50v)
* a little heatshrink (for Capacitor leg)
* Small Glue Gun (Again, nice & cheap {takes 7mm Glue Sticks}!!!)
* NO COFFEE or REDBULL for the day lol (im addicted to Energy Drinks so have REALLY shaky-hands!!!)

Settings Under Device Manager-PORTS-Prolific COMM port Properties:
i read somewhere on one of the forums that it would be a good idea to set the baud-rate (bits per second) to 57600 so this was the only setting here i tampered with, from what i read, it was so that the sketch upload doesnt 'time-out' if/when uploading big sketches, but since i'm still a learner this wouldn't affect me much just yet but i thought it be good practise to knoe where this setting was for when the time came to fully utilise it, lol

Settings Under Arduino IDE:
under tools - board - selected 'Arduino Uno'
under tools - serial port - selected 'COMM 4' (on my PC this was the only COMM Port !)
under tools - programmer - selected AVR ISP II (This was the 'default' setting !)

Physical Connections From USB Adapter to RBBB:
PL2303 Adapter:                       RBBB:
           DTR-----------------------------RST PIN

Followed you 'ible to the letter but when i tried doing the Function Test (STEP 2) and wrote some text in the Top-Box of the window that appeared (Shit+CTRL+M) and hit <Enter> --- the text didnt drop down into the lower text box which got me worried, but i thought 'what the heck, its trial & error time again', lol, so i opened up the Blink sketch, verified it, then hit upload......   .......   ...... took some time and voila !!! Worked like a charm !!!

Once again - A mighty-MAJOR thanks L.O.G - an extremely great 'ible worthy of legendary-status !!!

& also thanks for persevering with my newbie questions and for being so patient - i now stand on a triumphant field of victory thanks to you !!!

"All Hail L.O.G" (lol) !!!


msuzuki777 made it!(author)2012-05-25

Fantastic! Getting that first Arduino to blink is a major accomplishment. You are on your way.
I find that the Arduino Instructables are more helpful than Another good one is

By the way, since you have multiple Arduinos, you can hook up several at once. They will just be on different Com#s. On my main PC, I have my Arduino weather station connected all the time.


offtherails2010 made it!(author)2012-05-25

!!! DUDE !!!

LOG - Your a Saviour !!!

Seriously, many thanks once again, ive done the same Cap-soldering hack on my 2nd PL2303 and thats also working like a charm !

i used a 2-part plastic-weld glue to secure the DTR pin (i use this glue alot, lol) but have recently picked up a batch of clear potting resin that im going to encase the whole USB Module into (only because i accidently shorted a USB module in the past as it was lying on a wire-link i had forgot to send to the trash! ), just got to make sure not to fill the holes of the usb port and have it sticking out of the mould a little so it will still connect into a female USB Port!

Yeah i share your advice, instructables arduino guides are much easier to digest than, if only they followed-suit, lol, & ive been studying for a few weeks now and its full of great stuff too!

Quick silly question though, lol, can i connect multiple RBBB's to a single PL2303, or the more likely story, would every RBBB need its own PL2303 - hence having a different COMM port assignment ??!!!??

Thanks again LOG - Your Legendary !

msuzuki777 made it!(author)2012-05-26

You can connect only one RBBB per PL2303 but you can have many COM ports with separate PL2303s. I seem to remember having a COM23.

Good idea to pot your PL2303 modules.


offtherails2010 made it!(author)2012-05-29

howdy LOG, just wanted to furnish you with some new pics of the potted PL2303 !

My very 1st time using casting resin so didnt turn out too bad for a crude 1st effort, if i dont say so myself, no more shorting out & blowing my usb adapters from now-on (especially after all the hard work of delicately putting it together, lol !) !!!


msuzuki777 made it!(author)2012-05-29

Very nice.
I like the clear so you can still see the LEDs.


offtherails2010 made it!(author)2012-05-29

many many thanks LOG - ive got this instructable as one of my speed-dials on my web browser !

Couldn't have done it without your help - many thanks once-more !

msuzuki777 made it!(author)2012-05-31

Glad I could help. Let me know if you get stuck on future projects.


offtherails2010 made it!(author)2012-05-26

Thats what i thought, good to know from the beginning i'll need a separate PL2303 per RBBB !

Once again, many thanks for the truly AWESOME instructable LOG !!!

Keep up the Great-Work !!!


About This Instructable




Bio: Lazy Old Geek
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