Using Cheap Asian Electronic Modules
By Jim Rowe
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, 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 under a tenner, or a
little more if you want it in a case
rather than just a bare board.
W
hen I first spotted 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 about) £5.60 plus £2 for airmail – a total of just £7.60! I was curious and so decided to order 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 £12.75 plus £2.50 air
parcel shipping. 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 single 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
36
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
Nearly all of the components are located on the underside of the LCR-T4 multicomponent tester module.
Practical Electronics | March | 2022
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 devices 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.
Here’s the LCR-T4 testing an NPN transistor (an AY1103 which was made by
Fairchild Australia).
Geekcreit LCR-T4 Mini Multitester
Practical Electronics | March | 2022
Reproduced by arrangement with
SILICON CHIP magazine 2022.
www.siliconchip.com.au
37
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:
https://bit.ly/pe-mar23-lcr
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...
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%.
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
38
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
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 LCR-T4, 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 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.
The TL431AN voltage reference allows the MCU’s analogue-to-digital
converter (ADC) to measure device
voltages accurately.
Practical Electronics | March | 2022
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. Silicon, germanium or schottky diodes
It displays the anode 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. 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
base-emitter 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. Darlington transistors
It’s claimed to be able to test 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.
between 25pF and 10µF, and obtained readings accurate to
within ±2% over this range. Not bad for a low-cost tester.
9. 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 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 (PE,
February to April 2013), you will see that there are huge
differences 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.
4. 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 gatesource capacitance, Cgs.
5. Enhancement-mode MOSFETs
For these far more common MOSFETs, it again shows the
G-D-S pin connections plus the orientation of a protective
diode if it finds one. It also indicates the gate-source threshold voltage (‘Vt’) and the gate-source capacitance, Cgs.
6. SCRs and Triacs
It just identifies them and shows their pin connections.
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7. Resistors
It measures and displays the resistance. The rated measurement range is from 0.1Ω to 50MΩ, and when I checked
a fair number of reference resistors, it gave readings better
than ±2% for values between 50Ω and 2MΩ.
Below 50Ω, the error gradually rose to +7% at 10Ω, while
above 2MΩ, it gradually increased to −4.4% at 50MΩ. That
isn’t wonderful, but not bad for a low-cost tester making
two-terminal measurements.
8. 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
Practical Electronics | March | 2022
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