The first thing I did was to spray the package with disinfectant inside the garage trash can. Then I opened it up and sprayed the inner package. I have no desire to catch what seems to be a very nasty virus.
I've been waiting for this to arrive since I placed the order in January, and it finally got here! What could be so exciting that just arrived from Thailand? It's a build-your-own curve tracer. To be more specific, it's the signal supply part of a curve tracer. It comes without build instructions, but it comes with directions on how to get them. I'm guessing English is not the primary language of whoever printed the little label inside :)
Traces on both sides! Most exciting.
This device was ordered from Thai Kits, a supplier of hobby electronics kits. When assembled, it should look something like this.
What is a curve tracer, you might be wondering, and why would anyone even want one? To answer that, we need to understand how voltage and current change with respect to each other when small amounts of AC voltage are applied to a component.
Below: In a purely resistive circuit, the AC voltage and current are in phase with each other. A resistor does not alter the relationship of voltage and current - they peak and pass through zero at the same moment. See the image below for the circuit diagram (left) and the resulting voltage and current waveforms across the resistor.
Below: In a purely inductive circuit, a coil of wire (an inductor) replaces the resistor. As the AC current flows through the circuit, the coil of wire builds up a magnetic field, and that magnetic field resists changes in *current* flow. As a result, current flow lags voltage by 90 degrees in a purely inductive circuit. See the image below for how the inductor phase-shifts current behind the voltage waveform. The voltage peaks first, then the current peaks 90 degrees later.
Then there are diodes and transistors, which typically don't conduct until a certain threshold voltage is reached, at which point they pass 100% of the current. When reverse voltage is applied, they don't conduct at all. Transistors can also be used as amplifiers, so they have gain that can be measured.
What is useful though, is that you can apply a very small AC voltage to a component, and quickly determine if it is faulty or not, using an oscilloscope. Most oscilloscopes have a special mode, called "X-Y Mode" that allows voltage to be input on the X axis, and current to be input on a separate channel and displayed on the Y axis. The oscilloscope can now display what is called a "Lissajous curve" - basically how the current and voltage are behaving with respect to each other on separate axes.
The video below explains some of the bench-top practical use of a I-V curve tracer. His simpler test device is called an "Octopus", but an Octopus and a Curve Tracer do the same thing. The curve tracer I purchased has an adjustment for higher and lower power components, and a polarity reversing switch for different types of transistors.
You can use this method to match components, if you need a very fine match. For example, you might want to precisely match the amplification curves of a pair of transistors for a transmitter or a stereo amplifier.
In the video below, the tech is builds and tests the same device I just purchased. It looks like it will be a fun project. I still need to purchase a power supply and hobby box. But this really looks like a cool build.
In the video below is the real deal: A legitimate Tektronix 576 curve tracer for use in labs and manufacturing/development. This bad boy is completely out of my budget, unlike the little Thai Kit.
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