Over the break, I got to play a bit with the Saleae Logic 8 logic analyzer. Its the mid-range model from Saleae, and it works with Ubuntu. I wrote about the predecessor to the Logic 8 a while back, before Linux support was around. I finally got to do a bit of tinkering with the new device, under Ubuntu Vivid.
The device itself came packaged only in the carrying case that is provided. Inside the zippered carrying case was the Logic 8 itself, 2 4×2 headers with 6-inch leads, 16 logic probes, a micro-usb cable, a postcard directing you to the support site, and a poster of Buzz Aldrin in the Apollo cockpit.
The Logic 8 is made out of machined anodized aluminum and is only about 2×2 inches. It’s sturdy-feeling, and the only ports are the micro-usb to connect to the computer, and the 16 logic probe pins (8x ground+signal). There’s a blue LED on the top.
The test leads seem pretty good. I’m used to the J-hook type leads, and these have two pincers that come out. I’ve been able to get the leads into more places than I would have with a J-hook type logic probe.
Another really interesting feature is that this logic analyzer can do analog sampling. Each of the Logic 8 test leads can perform analog sampling. The device can sample faster if you’re only using one analog channel. One channel can sample at 10M samples/second, and running all 8 will sample at 2.5M samples/second. According to the literature, frequencies above the Nyquist frequency of the sample rate get filtered out before hitting the onboard ADC. If you’re anything like me, most of the my electronics tinkering doesnt require me to look at signals above this sampling rate, and I could see using the oscilloscope less and using the Logic 8 for some analog signals work too.
Underside of Logic 8
The Logic 8 software is available (freeware, closed source) on the website and will simulate inputs if there’s no device connected, so you can get a pretty good feel for how the actual device will work. It was largely hassle-free, although I did have to unpack it in /opt because it wasn’t packaged. Overall, it was pretty intuitive to configure the sampling, set up triggers, and test my circuit. The look and feel of the software was much better than a lot of other electronics tools I’ve used.
Trying it out:
I was working on a pretty simple circuit that takes a sensor input and outputs to a single 7-segment. Its composed of a BCD-7segment decoder chip and an ATtiny13. (easy enough to program with the ubuntu packages ‘avrdude’ and ‘gcc-avr’).
Circuit Under Test (ATtiny13, a light sensor, and a BCD to 7 segment decoder)
Its not electrically isolated from the circuit, but I would expect that for the price point. Just make sure that you don’t have any ground loops between your computer and the circuit under test. I don’t typically build circuits that really need a earth-ground, so I don’t see that being much of an issue.
So, my first run, I connected it to the GPIO pins on the AVR and varied the voltage from 0-2.5V on the ADC pin.
ADC to 4bit digital
Yay, my circuit (and avr program) was working.
I am pleased with the Logic 8, and am even more excited to have a hassle free way to measure logic and analog signals in Ubuntu!