You Don’t Need That Bulky CRT Oscilloscope Anymore

While it might be nice to use a $4,000 oscilloscope in a lab at a university or well-funded corporate environment, a good portion of us won’t have access to that kind of equipment in our own home shops. There are a few ways of getting a working oscilloscope without breaking the bank, though. One option is to find old CRT-based unit for maybe $50 on craigslist which might still have 60% of its original 1970s-era equipment still operational. A more reliable, and similarly-priced, way of getting an oscilloscope is to just convert a device you already have.

The EspoTek Labrador is an open-source way of converting a Raspberry Pi, Android device, or even a regular run-of-the-mill computer into a working oscilloscope. It’s a small USB device with about a two square inch PCB footprint that includes some other features as well like a signal generator and logic analyzer. It’s based on an ATxmega which is your standard Arduino-style AVR microcontroller but geared for low power usage. It looks as though it is pretty simple to use as well, and the only requirements are that you can install the software needed for the device on whatever computing platform you decide to use.

While the Labrador is available for sale at their website, it is definitely a bonus when companies offer products like this but also release the hardware and software as open source. That’s certainly a good way to get our attention, at least. You can build your own if you’d like, but if you’d rather save the time you have pre-built options. And it doesn’t hurt that most of the reviews of this product seem to be very favorable (although we haven’t tried one out ourselves). If you’d prefer an option without a company backing it, though, we have you covered there too.

Better Stepping With 8-Bit Micros

The electronics for motion control systems, routers, and 3D printers are split into two camps. The first is 8-bit microcontrollers, usually AVRs, and are regarded as being slower and incapable of cool acceleration features. The second camp consists of 32-bit microcontrollers, and these are able to drive a lot of steppers very quickly and very smoothly. While 32-bit micros are obviously the future, there are a few very clever people squeezing the last drops out of 8-bit platforms. That’s what the Buildbotics team did with their ATxmega chip — they’re using a clever application of DMA as counters to drive steppers.

The usual way of driving steppers quickly with an ATMega or other 8-bit microcontroller is abusing the hardware timers. It’s quick, but there is a downside. It takes time for these timers to start and stop, and if you’re doing it two hundred times per second with four stepper motors, that clock jitter will ruin your CNC machine. The solution is to use a DMA channel to count down, with each count sending out a pulse to a stepper. It’s a clever abuse of the hardware, and the only drawback is the micro can’t send more than 2¹⁶ pulses per any 5ms period. That’s not really an issue because that would mean some very, very fast acceleration.

The Buildbotics team currently has a Kickstarter running for their four-axis CNC controller using this technique. It’s designed for Taig mills, 6040 routers, K40 lasers, and other various homebrew robots. It’s an interesting solution to the apparent end of the of the age of 8-bit microcontrollers in CNC machines and certainly worth checking out.