Velleman VM205 Oscilloscope
les pounder takes a look at a simple oscilloscope that offers to resurrect that Raspberry Pi sitting in your project box.
Les Pounder takes a look at a simple oscilloscope that offers to resurrect that Raspberry Pi sitting in your project box.
Velleman is well known in the maker world.
It sells kits from simple flashing LEDS to dualextruder 3D printers, and also this oscilloscope shield for the Raspberry Pi.
Originally designed for the first model of Pi, with 26 GPIO pins, the Velleman VM205 attaches to all models – but for 40-pin models you need to ensure that the shield does not touch any components, as the included standoffs only match the original Pi layout. The input connections are made via a breakout connector that provides a series of single-core wires which can be inserted into breadboards or screw terminals. We used some Wago 221 connectors to lock the thin wires in place, and then make connections with jumper jerky wires. With the shield attached to the Pi, power up and then set up the SPI interface so that the Pi and shield can communicate. The included instruction book is sparse and out of date, but for the target audience there is enough for the maker to adapt and reference.
Using the VM205 is managed via custom software. The interface is ugly but simple, which enables us to focus on the job. The VM205 has 10 logic analyser channels that means we can peek into 10 components in a circuit, and each of the channels are graphed in the bottom section of the chart. Here we can ‘see’ how a chip works. For example, we connected our Aneng AN8008 multimeter and used the built-in frequency generator to create a series of waveforms from 50Hz to 5khz. All of these waveforms were visualised successfully. We then connected a voltage to the VM205 and were able to measure the voltage change as we altered the input voltage. This leads nicely into the input voltage range, which is up to 30V thanks to a part of the circuit that enables the use of such high voltage while protecting the Raspberry Pi’s fragile GPIO.
So what can this board detect? Well, it has a sample rate of 1MS/S (megasamples), which is rather low when compared to professional scopes that offer GS/S (gigasamples) – but it’s good enough for the price of this unit. The VM205 can measure up to 100khz signals and can work with AC and DC power. It can record 800 samples and features a simple 8-bit analogue-to-digital converter. So what does that all mean? That this is not a professional oscilloscope – but we kind of guessed that by the price. It’s brilliant if you accept that it is a first step into this technology. It can be used to diagnose issues with your projects and other electronic devices – just make sure that you are careful with the voltages!
Oscilloscopes and logic analysers are handy things, but they are expensive and somewhat large. So dipping your toes into the water with the VM205 should prove enlightening and possibly inform purchasing decisions for a hobbyist-grade scope. What we really like about the Velleman VM205 is that it can be used with the older Raspberry Pi models, and keen hackers could quite easily add a small screen and combine the scope into a nice professional package.
This is a fun, gentle and cost-effective introduction to oscilloscopes for new users. For sheer value for money this is a great scope that also revives that old Pi 1 you have in the project box.