When Gabriel Anzziani from gabotronics.com asked me if I would like to do a review of the XMEGA Xprotolab I said yes because although these small devices cannot replace a real tool in an electronics lab, they often serve as development boards for the devices used on them. The Xprotolab is a miniature mixed signal oscilloscope and waveform generator packed in a DIP module which makes it great for breadboards. It has a nice set of features for such a small device:
for oscilloscope mode:
- 2 Analog Channels, 8 Digital Channels
- Maximum Sampling rate: 2MSPS
- Analog Bandwidth: 320kHz
- Resolution: 8bits
- Input Impedance: 1Mő©
- Buffer size per channel: 256
- Max. Input Voltage: +/- 10V
for arbitrary waveform generator:
- 1 Analog Channel
- Maximum conversion rate: 1MSPS
- Analog Bandwidth: 44.1kHz
- Resolution: 8bits
- Low output impedance
- Buffer size: 256
- Max. Output Voltage: +/- 2V
The hardware is based on a ATXMEGA32A4 coupled with a Graphic OLED display 128◊64 pixels and a TL064 quad op-amp for the analog side.¬†What is not mentioned on the product page is that it also has FFT, Meter mode with voltage and frequency, X-Y mode and a logic analyzer. Sound nice but lets put it to the test and see how it performs.
First thing I wanted to test on the xprotolab is the meter mode; I think for beginners who build breadboard circuits it will be a very useful feature because you could use your multimeter to check some voltage or current while you use the xprotolab to check another voltage or frequency. Every electronics lab should have at least 2 meters to serve this purpose but if you’re a beginner its most likely you only have one. I must tell you that Gabriel was very helpful when I discovered some bugs in the firmware and he corrected them within hours. Unfortunately it is a work in progress and I could find other bugs even after upgrading. The firmware version used during tests is 0.95.
So to start testing I placed the xprotolab on a mini breadboard and supplied power at 5V. First thing to notice is the OLED display which is a very good choice for this application and provides nice & crisp display with good contras. The menu is not difficult, it takes about 10 mins to get used to it and learn what each menu/key press does. After switching to meter mode (VDC) I applied a 3.3V voltage through a 10k series resistor to CH1 and CH2. With both channels connected to the same signal at the same time CH1 was reporting 3.22V and CH2 3.28V while my multimeter was reporting 3.24V so CH1 was off by -0.02 compared to the multimeter while CH2 was off by +0.04. A slight offset between channels can be noticed ~0.06V. The firmware has an offset compensation feature which can be accessed by holding key 4 during power on.
After entering the offset menu it will ask you to ground all inputs and press start. I did that.. it¬†acquired¬†the new offset values and I continued using into meter mode to see how it affected the results. Connected to the same signal as earlier CH1 was now showing 3.19 V which is off with -0.03 compared to the multimeter but the surprise is that CH2 is not taking any measurements, its just stuck after the offset compensation. As you can see the values are pretty close to what the multimeter was reporting and really a 0.02 offset is not a big deal in most applications, but the software has a bug that’s preventing CH2 from taking measurements after the offset compensation. To fix this I just re-flashed the EEPROM and CH2 started working on meter mode again.
Next I tried the frequency measurement. I used a signal generator with a sine wave and the xprotolab was able to detect frequency down to 10Hz and up to 500KHz which is pretty good for a device so small and inexpensive. Next I tried the VPP meter mode which was able to detect values on a sine wave up to 100KHz, any frequency higher and the measurement got all weird.
Next test was on scope mode, and I was able to get a clean and accurate reading on CH1, up to 100KHz sine wave. Anything higher than 100KHz caused false readings and I could notice the amplitude going down.
I also did tests with square and triangle wave shapes and the results were the same. I did not have enough time to review the other features like the arbitrary waveform generator or the logic analyzer but I’m sure I’ll use it somewhere in a future project cause if you remember I wrote a post about how nice is to have a logic analyzer when debugging. There is one feature I felt it was missing from it though , the value of the frequency printed on the screen while taking scope measurements.(later edit: Gabriel pointed out that this feature exists and he was right, I somehow missed it. You have the option of activating and locking the cursors and this will show the frequency on the screen as 1/deltaT but I feel the position its not the best as it overlaps with the represented signal). ¬†This is a feature commonly found on all modern scopes, and although you have the options of controlling two cursors from the menu its easier to just have the value on the screen without having to use the cursors.
To conclude the Xprotolab is a small and cheap device which besides the features enumerated above doubles as a development board with schematics and source code offered on the product page. To me its clearly visible that someone has put a lot of work into this project and is using every bit of processing power from the ATXMEGA32A4 to crunch the numbers.