Today I received my metal cased “DSO Quad” (V2.6), a hand-held four channel portable oscilloscope I’d recently ordered from Seeed Studio. This post summarises some useful links, the device’s basic capabilities and a couple of photos.
A community of interest exists around the DSO Quad (also known as the “DSO203”) and its open source hardware and firmware (although Seeed Studio’s source code releases seem to lag the version of their latest binary releases). The official tech wiki is here.
Seeed Studio’s DSO Quad
I purchased mine direct from Seeed Studio (the product’s developers) because they offered a black metallic case version (cf. earlier plastic versions) with two regular “1x” analog probes and two digital probes included. Since the hardware design is open, a number of alternative sources exist (e.g. DealExtreme, SparkFun, Goodluckbuy, etc) but they tend to differ in terms of how many probes are included and using a plastic case.
The gallery above provides a close-up view of the DSO Quad itself and everything in the box. Note that Seeed Studio’s DSO Quad did not come with a USB-to-miniUSB connector cable (required to both charge the unit, and transfer files and firmware), but such cables are not hard to find.
Analog sensitivity & resolution / Screen size
According to this manual (manual version 0.92b for the DSO Quad v2.6 hardware), the DSO Quad provides two analog inputs with a claimed range from 20mV to 10V per division onscreen at 8 bit resolution (i.e. you’ll resolve voltages to 1/256 of full scale). The screen is a 400×240 pixel, 3″ TFT colour LCD.
The two analog inputs, two digital inputs and one analog waveform output are provided via “MCX” sockets. You either need probes specifically terminating in MCX plugs (e.g. these digital probes from Seeed Studio) or purchase MCX-BNC adapters so you can use more conventional probes having BNC plugs.
The DSO Quad is based on ARM cortex M3 (STM32F103VCT6) processor. Seeed Studio claims their integrated FPGA and high speed ADC provides a 72MS/s sampling rate per channel. The DSO Quad also presents itself as a 2MB USB disk when plugged into a regular PC, providing the means of transferring data between the oscilloscope and the outside world.
The calibration process for channels A and B on my DSO Quad differed from that in the manual. The Quad will automatically cycle through zero’ing out the various levels, you do not need to do that yourself (despite what it says in the manual).
To provide a measured voltage source for the different ranges, I used a 5K potentiometer across a 6V battery source (4×1.5V AA) and fed the middle terminal out to the DSO Quad and a digital multimeter (in parallel with each other). Using the pot I set different voltages for each range, then adjusted the DSO Quad (using the calibration control) to match the multimeter’s reading.
Note: since the DSO Quad has only 8-bit resolution on each analog channel the calibration adjustments were quantised to 1/256th fractions of each voltage range.
Example — internal signal generator via RC circuit
(Added September 2012) The screenshot below shows the internal waveform generator configured to emit a 1kHz step sawtooth, which is connected directly back in to Channel A. Channel B is observing the same waveform via an RC circuit that is smoothing out the transitions. The timebase is 200usec, and we’re triggering on downward edge of Channel A (light blue).
The actual circuit details are not important — I can’t even recall the R and C values. It created a distorted version of the sawtooth, which was good enough to illustrate both analog channels operating at the same time.
I’ll post comments regarding firmware and internal architecture at some later date(s).