Review: Mini Scope

DSO150

As already mentioned, I found the oscilloscope kit DSO150 (picture) while browsing the manufacturer’s website [1]. It is a development of the DSO138 using the same display and controller. This model is, however, only available as a kit with a case. Apart from the input coupling selector switch, the entire operation is controlled by four push buttons and a rotary encoder. For such a basic scope you really don’t need anything else.


The DSO150 with a i KHz sine wave filling the screen.

The kit is supplied with all the SMD components already mounted on the board. Some components need to be soldered before assembly and testing. Anyone with a little experience with a soldering iron should not have any problems and the instructions are quite clear. Sold as a kit of parts, the unit it not subject to the standards and regulations that would normally apply to finished equipment.

The biggest drawback I discovered when I first switched on: the zero level disappeared as soon as the supply voltage levels changed. A quick look at the supplied schematic was enough to identify the problem: the DSO150 doesn’t use voltage regulators to stabilize the input amplifier supplies! Also a Zener diode is used to provide the input voltage offset level for the ADC, which is less than optimal. I guess you only get what you pay for. On closer inspection however the hacker in me saw there was some opportunity for improvement. Fortunately there are through-hole resistors in series with the supply rails so it’s a fairly easy mod to replace these with 78L05 and 79L05 linear voltage regulators. The supply to the Zener diode was transferred to the stabilized 5 V and bingo, the zero line became stable.

As with the DSO138, the voltage offset is a digital value added or subtracted from the measured input samples by the MCU. The amplitude for full modulation is 640 mV_pp, which is only about 20% of the ADC input range. The visible interference on signals with the DSO150 however was significantly less and occurred less often compared to the DSO138. An external trigger input can also be easily added to the DSO150.