![]() ![]() The English PDF is 103 pages, explaining theory of operation, the circuit itself, and the software. The Subversion repository for the project shows it is quite active, with the most recent check-in only a few hours ago. It turns out the transistor tester is an open source hardware project ( translated) originally created by, and built upon by and a number of others. Some digging turned up the history on this device. 91make is a seller on , often referred to as “China’s ebay.” 91make’s front page features no less than 7 versions of the transistor tester, with various cases and LCDs. So what exactly is driving this little tester? There are about 20 versions of it on the market, all of them from China. While I don’t have a calibrated lab to check against, the numbers lined up with my Fluke meter. The values returned were all reasonable as well. Regulators are a bit more than a simple device though, so I can’t blame the tester there. The only thing it balked on was a linear voltage regulator, which showed up as two diodes. The tester worked surprisingly well – it was able to correctly identify BJTs, FETs, even esoteric parts. The tester showed hFe as 216, and forward voltage as 692 mV, both reasonable numbers for a 2N2222. Flipping the pins around and re-testing worked as well. The damn thing worked – it showed the schematic symbol for an NPN transistor with Collector, Base, and Emitter connected to Pins 1,2,and 3 respectively. I pulled an old 2N2222 in a TO-18 metal can, and popped it in the tester. Capacitors – ceramic disc, electrolytic, and surface mount all worked as well. I had a few resistors lying around the bench (doesn’t everyone?) so I put one in. Since I didn’t have anything in the socket, it quickly lit up and displayed its maker information – “”, and “By Efan & HaoQixin”, then it informed me that I had “No, unknown, or damaged part”. Hooking up a 9 volt battery and pressing the magic button brought the tester to life. I didn’t have huge expectations for the tester, but I hoped it would at least power up. Supporting it are a few transistors and a handful of passives. The circuitry was open for all the world to see on the bottom of the tester. Fitting the LCD back into the acrylic backlight frame revealed a slightly worrisome twist in that same flex. Thankfully nothing was actually damaged, though I do want to give the flex cable some protection in the future. My particular unit arrived with the LCD flapping in the breeze, hanging on by its flex cable. This thing is built cheap – as cheap as the factories can make it. ![]() I’m going to get the obvious out of the way. Two days later I had a “SainSmart Mega328 Transistor Tester Diode Triode Capacitance ESR Meter MOS/PNP/NPN L/C/R” in my hands. Curiosity got the better of me and my mouse found its way to the “Buy it now with one click” button. I’ve been seeing those testers around quite a bit lately. Their customer database paid off when it recommended a $22 transistor / component tester. Every time I log in, I’m presented with a list of new Blinky LEDs, Raspberry Pi accessories, Arduino shields, and the like. Amazon has been getting creepier and creepier lately with their recommendations. ![]()
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