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Using Cheap Asian Electronic Modules By Jim Rowe The Geekcreit LCR-T4 Mini Digital Multi-Tester It’s hard to believe, but you can get a compact digital tester which will identify, check and analyse bipolar transistors, JFETs, Mosfets, diodes, LEDs and thyristors, resistors, capacitors and inductors for less than most joints charge for lunch these days! The Geekcreit LCR-T4 does all of the above and will cost you about $12.50, or more if you want it in a case rather than just a bare board. W hen I first saw the Geekcreit LCR-T4 advertised on the Banggood website, I thought it was too good to be true. It was described as a “128x64 LCD Graphical Transistor Tester Resistance Capacitance ESR SCR Meter”, priced at only $8.74 plus $3.94 for airmail to Australia – a total of just $12.68! I was curious and so ordered a couple straight away. When they finally arrived (about five weeks later), unfortunately, I found that one of the two LCR-T4s was damaged in transit. There was a chunk of glass broken off the top right of its LCD panel, and the bottom half of the screen wasn’t working. Luckily, the other unit worked fine, so I was able to proceed with the review. I then discovered that it is also available with an assemble-it-yourself clear plastic shell, for $21.18 plus $3.93 air parcel shipping – a total of $25.11. I ordered one of those as well, based on my positive impression of the ‘naked’ version, but it hasn’t arrived yet. Components and construction The multi-tester is built on a sin98 Silicon Chip gle PCB measuring 73 x 60mm. The only components on the front are the 128x64-pixel LCD panel with green LED backlighting, a 14-pin ZIF socket used to connect to the device being tested, and a pushbutton switch to initiate testing. The rest of the tester’s components are on the rear of the PCB, including an ATmega328 MCU (microcontroller unit), an 8MHz crystal, a 78L05 regulator, a TL431AN 2.5V voltage reference, three small SOT-23 bipolar transistors, two 1N4148 diodes and a handful of passive components. The tester uses a 14-pin ZIF socket because it provides a range of options when it comes to components with different pin configurations and spacing. Although there are only three inputs (logically labelled 1, 2 and 3), the two rows of seven pin positions on the ZIF socket are connected in this order: 1-23-1-1-1-1 (left to right). This gives you quite a bit of flexibility for connecting different devices. There’s also a small ‘D-PAK’ type array of plated copper pads for receiving SMD components, just to the right of the ZIF socket. Presumably, SMD deAustralia’s electronics magazine vices to be tested have to be pressed against the PCB to make decent contact during testing. The complete tester is powered by a standard 9V battery via a battery clip lead. It’s straightforward to use What, no power switch? Well, the pushbutton switch on the front of the PCB does everything. If it hasn’t been pressed, the tester is in ‘sleep’ mode with its current drain from the battery less than 20nA. When you do press the button, the tester springs to life. The LCD backlight immediately turns on, and the screen displays the message “Testing ...”, together with an indication of the battery voltage, like “[Vbat = 9.15V]”. Then the tester starts checking to see if anything is connected to the inputs. If it doesn’t find anything, it displays a large question mark, plus the message “No, unknown or damaged part”. But if it does find an NPN or PNP bipolar transistor, a JFET, a Mosfet, a diode, an SCR, a Triac, a resistor, a capacitor or an inductor connected to the siliconchip.com.au inputs, it works out the component’s configuration and shows it, together with some basic measurement data. And the test results are displayed for about 10-30 seconds after you press the button, before the tester turns itself off again automatically. The tester’s current drain during the actual testing is less than 25mA, so if you power it from a 9V alkaline battery, it should last for quite a while. No user guide Unsurprisingly, the LCR-T4 came without any user guide, or even any link to a source of such a guide. However, when I did a bit of Googling, I came across this link to a very detailed and informative ‘white paper’ as a PDF at siliconchip.com.au/link/ab49 It’s quite big (127 pages), and not that easy to read since it appears to be translated from German. It was originally written by Karl-Heinz Kubbeler (kh_kuebbeler<at>web.de), and in it, I was able to find some information on both the origin of the LCR-T4, how it works and how to use it. The original design, called the “AVR Transistortester” was first published by Markus Frejek in 2011, in the German publication “Embedded Projects Journal”. After that, Mr Frejek refined the design and added various enhancements. It wasn’t long before quite a few ‘clones’ of his tester began to emerge from China. At first, these variations-on-thetheme sported 16x2 LCD character displays and used an ATmega8 MCU. But soon, other versions started to appear with 128x64 pixel graphic LCDs and an ATmega328, ATmega1280 or even ATmega2560 MCU (with much more program memory). And so the Frejek transistor tester snowball kept on growing... Nearly all of the components are located on the underside of the LCR-T4 multicomponent tester module. wave generator with an output up to 2MHz and adjustable duty cycle and/ or a frequency meter with a range up to 1MHz. But they all seem to have the same basic features offered by the Geekcreit LCR-T4, with prices moving upwards according to the addition of those extra features. How it works As you’ve probably guessed by now, the LCR-T4 and the other clones of Mr Frejek’s tester work in much the same way. Given the relatively small number of external components, clearly, most of the hard work is done by the firmware running on the microcontroller. Many variants Nowadays there seem to be a lot of different variations on the original Frejek design, and you’ll find them on offer by many different vendors online. As well as the Geekcreit LCRT4, there is the Fish8840, the WEI_M8, the DROK, the FD_it TC-T7-H (also known as the DANIU LCR-TC1), the LTDZ_M328_7735 and the GM328A. Some of these come in a plastic case, others with an assemble-it-yourself case or just as a naked PCB module like the LCR-T4. Others have extra features like a built-in PWM square siliconchip.com.au Here’s the LCR-T4 testing an NPN transistor (an AY1103 made by Fairchild Australia). Australia’s electronics magazine February 2021  99 The TL431AN voltage reference allows the MCU’s analog-to-digital converter (ADC) to measure device voltages accurately. At the same time, the three small bipolar transistors enable the MCU to wake itself up and turn on the LCD backlighting as soon as the ‘GO’ button is pressed, then turn off the power and go back to sleep after the testing has finished. I think you’ll agree that it’s quite nifty. Hats off to Mr Frejek for his innovative thinking! Measurement features Now let’s look at the measurement data displayed for the different devices the LCR-T4 can test. 1) For silicon, germanium or schottky diodes, it displays the an100 Silicon Chip ode and cathode connections (ie, the orientation), the forward voltage drop (Uf), and the junction capacitance (in pF) when the diode is reverse-biased. LEDs can be tested as well, with the tester displaying them as a diode with a higher-than-usual forward voltage. 2) For NPN and PNP bipolar transistors, it shows the pin connections for the base, emitter and collector (B, E and C), the current gain, hFE (also known as Beta) and a voltage reading “Uf”, which appears to be the baseemitter voltage during low-current conduction. When I checked several silicon BJTs, the Uf readings were always over 600mV, while for germanium BJTs, the Uf readings were generally below 200mV. 3) It’s claimed to be able to test Australia’s electronics magazine Darlington transistors, giving the same parameters as for regular BJTs. But when I tried testing a few Darlingtons, it didn’t seem to recognise that they were Darlingtons and gave relatively low hFE readings. So I would not recommend testing Darlingtons with this device. 4) For JFETs and depletion mode Mosfets, it displays the pin connections for the gate, source and drain, plus the orientation of a protective diode if it finds one present. It also shows the gate-source threshold voltage (usually written Vgs, but labelled “Vt” here) and the gate-source capacitance, Cgs. 5) For the far more common enhancement-mode Mosfets, it again shows the G-D-S pin connections plus the orientation of a protective diode if siliconchip.com.au it finds one. It also indicates the gatesource threshold voltage (“Vt”) and the gate-source capacitance, Cgs. 6) With SCRs and Triacs, it basically just identifies them and shows their pin connections. 7) For resistors, it measures and displays the resistance. The rated measurement range is from 0.1W to 50MW, and when I checked a fair number of reference resistors, it gave readings better than ±2% for values between 50W and 2MW. Below 50W, the error gradually rose to +7% at 10W, while above 2MW, it gradually increased to -4.4% at 50MW. That isn’t wonderful, but not bad for a low-cost tester making two-terminal measurements. 8) For capacitors, it measures and displays the capacitance. The rated measurement range is from 25pF to 100,000µF, although for capacitors with very high values, the measurement time can extend beyond one minute. For capacitance values 1µF and above, the tester also displays the capacitor’s ESR (equivalent series resistance). I checked quite a few reference capacitors with values between 25pF and 10µF, and obtained readings accurate to within ±2% over this range. Not bad for a low-cost tester. 9) With inductors, it measures and displays both the inductance and resistance. The rated measurement range is from 0.01mH (10µH) to 20H. I checked 14 different reference inductor values from 27µH up to 1.09H, and obtained readings that were within ±6% for values of 1mH and above, but rising to ±30% for lower values. The series resistance readings given were all quite sensible. The bottom line After testing the LCR-T4 mini multitester fairly thoroughly, I think it’s a ‘little blooming wonder’ and excellent value for money. I have a few small gripes, though. One is the lack of any user guide, forcing you to search the web and digest Mr Kubbeler’s big ‘white paper’. Then there’s that lack of clarification for the exact significance of the Uf reading for bipolar transistors. And thirdly, in its naked form, the tester is really quite fragile – which explains why one of the two units I ordered was damaged in transit. So I’m looking forward to receiving the siliconchip.com.au The LCR-T4 can measure capacitors from 25pF to 0.1F with an accuracy of about 2%, and inductors from 10µH to 20H with a worst case accuracy of 30%. matching assemble-it-yourself plastic case that I ordered recently. One last comment: if you compare the LCR-T4 with my Semtest Discrete Semiconductor Test Set design (February, March and May 2012; siliconchip.com.au/Series/26), you will see that there are huge differAustralia’s electronics magazine ences between the two in complexity and cost. The Semtest offers more tests, but Mr Frejek’s design is clearly very elegant. So all in all, the LCR-T4 may not be a complete replacement for the SemTest, but it will undoubtedly make a very handy companion tester. SC February 2021  101