ScopeShunt Visualising The Current Waveform With Your Oscilloscope | Voltlog #310

We usually use an oscilloscope for visualizing a voltage over time but sometimes it’s also useful to visualize the current waveform over time. The right way to do it is to get a current probe which can sense the current and convert that to a voltage that the oscilloscope can display however such devices are pretty expensive, they can be around $1000 even for an entry level one like the Rigol RP1001C which is only rated up to 300KHz bandwidth.

But we can improvise something for a much lower cost and it should allow us to visualize the current waveform on the oscilloscope. You’ve probably seen me use a shunt resistor when testing power supply to take a look at the current waveform. Because as you know passing a current through a resistor will generate a voltage drop.

That voltage drop is directly proportional with the passing current and with a round value resistor we can have an easy to use transformation ratio between voltage and current. All we have to do is o introduce this resistor inline between our power supply and the device under test

For example if I have a 1ohm resistor, we have a 1:1 ration, for each mA passed through that resistor we will have  1mV of voltage drop that our oscilloscope can display. Such a circuit will of course have it’s limitations, for example it won’t work very well when testing low voltage low power devices because our resistor will introduce a burden voltage, which will drop our supply voltage to the device under test. This is also not an isolated measurement so it might not be safe when connected with higher voltage circuits.

But there are still a lot of scenarios where you could use this successfully on the electronics workbench so it might be worth building something like this. I want to make this nicer by building it inside an enclosure with the required bnc connector for connecting to the oscilloscope and 4mm banana plugs for passing the current through. I picked this small aluminium enclosure which would be enough to house the resistor, actually the resistors, because there are several advantages to using multiple resistors in parallel.

Alternative to this simple shunt resistor measuring method include the Joulescope which is a fully featured dc energy measurement test instrument with incredibly wide dynamic range that allows you to capture the smallest currents next to a jump to a higher current. I reviewed the Joulescope in Voltlog #211.

Voltlog #62 – Rigol DS1054Z Fan Replacement

Everybody knows this is a great scope for the money but as usual test equipment doesn’t use the best solutions in terms of cooling fans and associated hardware. They care mostly about keeping the unit cool and not about the noise the unit makes because usually these are used in environments where multiple equipment is run at the same time, the noise level is already high so it doesn’t matter much if a small 50mm fan is adding noise.

But it’s a totally different story for us hobbyists that are using these pieces of test equipment indoor, in our homes. We usually want units with passive cooling or with silent fans.

Voltlog #57 – InTheMail

Another InTheMail video because I know you like seeing these electronics items from China.

Here is a list with the items shown in this video:

  • Prototyping PCBs
  • Carbide PCB Micro Drill Bits Set
  • 1W 3W 5W 6x LED Aluminium Printed Circuit Board
  • 1W 3W 5W Star Shaped LED PCB
  • 20W Waterproof IP67 LED Driver
  • EL Panel 10cm x 10cm
  • 3V Flat Vibration Motor
  • High Voltage Boost 400KV Step-Up Module
  • Small Plastic Bottle With Needle
  • Gelid Silent 5 Cooling Fan Replacement for Rigol DS1054Z
  • 18650 Battery Storage Case
  • Small Plastic Project Box Black
  • 3P4T Rotary Selection Switch
  • NodeMCU ESP8266 Module with CP2102 USB to Serial
  • LM2596 DC-DC Step Down Module
  • HC-SR501 PIR Motion Detection Sensor Module
  • 2000W SCR Motor Speed Controller
  • LT1083 Power Supply Kit
  • Maiwo K104 USB 3.0 to 2.5 Inch Sata Hard Drive Cable Interface

As usual links for these items will be posted in the video description.