Arduino and CueCat Barcode Scanner




Introduction: Arduino and CueCat Barcode Scanner

I've had a cuecat barcode scanner sitting around for over 10 years. Basically it connects to a PS2 port (apparently there is a USB version) like a keyboard and spits out a barcode when scanned. Nice!. The annoying thing is that it is "encrypted". What I set out to do is;
- unencrypt the barcode in software on the arduino
    - i didn't want to cut into the Cuecat in case I broke it, not hard to replace, but that's not the point ;-)
   - get it to write only the bar code to the serial port, and I can use some terminal emulator (TeraTerm,Putty or SecureCRT) to write the data to a file as I furiously scan like a boss all items with a barcode in the house.

Step 1: Connecting the CueCat to Arduino

The cable connected to the CueCat is a Y cable that connected to a PC PS/2 port. The connection to the PC is a male adapter. There is also a female, that allows the PC's keyboard to share the port.

There is no continuous path between the 2 ports (Except Power and GND) as a multimeter and continuity test confirmed. So using the female port as a way to access the cuecat signal did not work.

PS2 female connectors are hard to find these days, so I cut the female connector from the cuecat and used that to break out the wires...

The Cue cat cable has 6 wires, marked on the board as 1-6

1. Brown (+5V)
2. Red (DATA Female connector)
3. Black (Clock Female Connector)
4. Orange (DATA Male connector)
5. Yellow (Clock Male Connector)
6. Black - Cable is thicker than other black (Ground)

When cut, the female adapter, has the following which will map to the connector inside the Cuecat as follows

1. Brown (+5V)
2. Red (DATA Female connector) to Orange(pin4)
3. Black (Clock Female Connector) to Yellow (pin5)
4. Bare wire (GND)

I tinned the wires with flux and solder to make them a little more durable, and wired them to a terminal shield on the Arduino.

Step 2: Getting the First Code

Since the Cuecat emulates the PS2 Keyboard, I used the Arduino PS2 library and examples to get a look at the first bar-codes.

The only thing to watch out for is;
- The CLK is used as interrupt, and so ensure you connect to a pin that supports interrupts
e.g. on the Mega 2560

External Interrupts: 2 (interrupt 0), 3 (interrupt 1), 18 (interrupt 5), 19 (interrupt 4), 20 (interrupt 3), and 21 (interrupt 2).

I used Pin 3... Which is a bit annoying as now all the pins are not on same side of the board :-( (first world problems)

And a few swipes, check all wires are connected right and ...


TIP:  Look at ASCII codes, NOT printable characters...
You can see I played with the code a little, as when looking at output there are always non printable characters, so I wrote the code to show the ASCII code.


OUTPUT ASCII value -> printed Character
International Keyboard Test:
[deleted for brevity...]

Note that there does not seem to be anything strange at the start, but the end is /13 which is a Carriage return, ie, end of the code

I did expect to see ALT-F10 being sent as on my linux box it kept minimising and expanding the window on each scan, and that is the keystroke that does that... if the Arduino doesn't see it, then I am OK with that...

Step 3: Decoding the Barcode



<SERIAL> is the unique serial number that each cuecat has. The idea being that the company distributing them can track what you scan. I don't see a need for this, so will ignore it.

<CODE> is the BarCode type. I dont have an exhaustive list but I have seen "E13", "IB5" etc. I would think this may help decide where to look up the bar code, as I imagine that there are many sources of barcode data. I imagine that books, food products and teh barcodes you print may be in different formats. I know that some barcodes are numbers only, some are a mix of letters and numbers

<BARCODE> the interesting bit :-)

OK so how to decode...

I trolled the internet and found lots of example code in various (non processing/arduino) format with little explanation. So I grabbed a reliable version that worked well on my Linux Box that was written in PERL.

Here is the amazingly terse PERL script by Larry Wall

To describe it, and understand it, I did it in excel as follows... the file is attached to play with.

1) Break the code and break into the 2 pieces described above, and decrypt one at a time as described 
2) Each set of 4 characters is "unencrypted" into 3. So the length of the final output is 3/4 of the input string, Round down if necessary. (encryption going the other way clearly needs to pad out characters to ensure no information is lost)
3) Take the 4 characters and map to ASCII
             - effectively "a-zA-Z0-9+-" maps to ASCII characters 32-96 (ie SPACE ' ' to '_')
             - so E, N, b, X map to >, G, !, X respectively

I found it a problem to keep converting back and forth between ASCII characters and Codes (E.g. E<-> 69) as some non printable characters were hard to troubleshoot and working out which non printable character was being printed is tough. So in the final code I worked exclusively in ASCII codes until the last step. IE the yellow lines were useful while reverse engineering this, but are not part of the final code...

4) Subtract 32 from the ASCII code
             -  >, G, !, X has teh ASCII code of 62,71,33,81
             - Subtracting 32 gives us 30,39,1,49
5) Treat the above characters and ASCII codes as 6 bit numbers (4 x 6 = 24 bits)
               - 30 gives us 01110, so
               - 30,39,1,49 gives us 0 1 1 1 1 0 1 0 0 1 1 1 0 0 0 0 0 1 1 1 0 0 0 1
6) Treat the binary string as a string of 8 bit characters, this is how it becomes 3/4 of the size! (3 x 8 = 24 bits)
               - 0 1 1 1 1 0 1 0 0 1 1 1 0 0 0 0 0 1 1 1 0 0 0 1
               - 122, 112,113 which is z,p,q in ASCII format
7) Take each of the 3 codes and Exclusive OR it with 67 = 01000011
               - 122 XOR 67 = 57

122 = 01111010
 67 =  01000011
            00111001 = 57

                 - 122, 112,113 becomes 57,51,50
8) Convert to ASCII
          - 57,51,50 becomes 932, which is the first 3 digits of my barcode!!!!

9) repeat for each 4 digits until you get a '.' :-)

Step 4: Putting It All Together

So now we had read the data in and unencrypt it, so I mashed that together into a program for the Arduino... 
I made the format CSV style so I can cut and paste into EXCEL or upload easily...

I tried to make it into a library, but it is buggy and I ran out of time :-(

I will add the library later if I get it done...

Step 5: Last Points

As I was finalizing I noticed some errors crept in. the cucat seemed to scan in some incorrect characters. the deencryption is working reliably, but characters read in were bad. not sure If I broke something poking around inside it.

If you try it and it works, let me know.

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    8 years ago on Introduction

    great barcode scanner .net, after seeing it's discription i think i need to try it to scan barcodes  .do i need to buy liscence or it is free open souce.


    10 years ago on Introduction

    The CueCat uses an almost trivial XOR decoding scheme. Since the company only provided decoding (and spyware) software for Windows with the product folks in the Linux community performed a clean reverse engineer (no access to the software or even internal hardware of the CueCat) were able to figure out the coding scheme fairly quickly. Here's one writeup for how the decoding works.

    There's a wide variety of mods to the CueCat - declawing it (disabling the unit's individual serial number) and neutering it (eliminating the serial number all together and the encoding scheme). The first amazing part about neutering a CueCat is once it's done the CueCat becomes a plaintext general purpose bar code reader which simulates a keyboard without any drivers needed. Just plug it in and any scanned barcodes are automatically "typed". The more amazing part is the mod to neuter a cat is trivial - soldering in a single wire to the appropriate already existing pass through hole on the circuit board! The entire process takes about 10 minutes and can be done by anybody with novice soldering skills, in fact some folks do it without _any_ electronics skills, just reusing a bread twist-tie as a wire and squeezing the wire into the appropriate location.

    The mod is actually less invasive than what you've done to attach the PS/2 cable to the Arduino.

    One caution is there are many revisions to the circuit, fortunately documented in the circuit board's silkscreen. Here's one website with info on how to do the mod on all of the known revisions to the circuit board.


    Reply 10 years ago on Introduction

    Beware, not every cuecat is listed on the lincomatic page. The last one I modified required cutting a ground trace rather than jumpering a pin. That is because this model (maybe one of the last ones before switching to USB?) has the pin that signals "encrypt the output" wired to ground instead of floating, so if you jumpered +5 volts to that pin, you would just be creating a short circuit. Also, it looks like they stopped conveniently breaking out holes to wire it to.

    This model was k023a016 REV:C, I don't know how many others not documented on that original site there were.


    Reply 10 years ago on Introduction

    Too true....
    In this case, it was like climbing the mountain. It was there :-)

    And I don't have PS2 port on my laptop :-)


    Reply 10 years ago on Introduction

    It's trivial to add a PS2 port to a laptop (or any computer without PS2 connectors). Just get a 99 cent adapter cable - it lets you plug in two PS2 devices (typically keyboard and mouse) into a USB port. I use one to hook up my netbook to a PS2 KVM switch.

    The PS2 to USB adapter works fine with the CueCat.


    10 years ago on Introduction

    You may not have broken your cue cat, there may just be something extra or weird in the output normally. When I made my device (the meowing handheld scanner at the top of the related list to the right) I struggled for a long time trying to decrypt the data in software on the arduino. I kept getting extra characters like you do. I finally just gave up, since I was already cutting off the tail, and declawed the cuecat.

    It would be nice to get an all software fix working, because then my project could be more versatile.