Equipment Review: A first look
TFT GM328 Transistor Tester Diode LCR ESR meter
PWM Square wave Generator
I was looking for a simple capacitance meter as a spare and to backup up what I already have (I like to have at least two of everything so I can compare results). I found the unit above on Ebay and was amazed at what it could do. It is not particularly accurate in some situations, but any reading is better than no reading. It does many things, probably none of them particularly well, but it is cheap and everyone should have one!
I suppose every radio shack should have some test gear – a soldering iron and a couple of digital voltmeter for starters, an SWR meter and maybe a power meter for seconds. The unit above along with a nanoVNA would nearly complete a shack as long as you had a modern HF transceiver.
Ebay has the unit above for sale from dozens of
suppliers for between £10 and £14. Search on the rather unwieldy title
above. The design has been around for a long time and I am unsure of its
original heritage, maybe it was a
2011 Embedded Projects Journal article by Markus Frejek? If anyone knows, please let me know.
There are details on the website
https://www.mikrocontroller.net/articles/AVR-Transistortester
and the EEVBLOG website has a extensive forum discussing it at
https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/
Older
versions had simple 2 line text LCD screens, the recent ones have
colour TFT screens so make sure you buy one that looks like the photo
above.I will summarize what it can do here, although to date I have just
used it to measure a few things I do believe it is a Swiss army knife
of component testing!
Features of the GM328A;
Versatile
connections; by using a zero insertion socket, inserting components is
eas y, pick the correct pitch, insert and push the lever down.it does
not matter which connections you use, for resistors, capacitors and
inductors just pick any
two two pins. If you plug in a diode or
transistor it will work out what pin is which, this alone makes it a joy
to use, it can identify which pin is the base, collector or emitter as
well as telling you the polarity (NPN or PNP) and the gain, and the Vbe.
And similarly for MOSFETs and so much more.
There
is even some SMT pads where you can hold SMT parts to test as well.
Works best if you have three hands though. The unit can measure
Resistance, Capacitance and Inductance. Capacitors over 20nF also have
their ESR measured. NB discharge caps before connecting them. I inserted
a 1mH choke the unit
measured 1.05mH and when inserting a 10uH it gave .01mH so the readings were ok.
I couldn’t measure the small capacitance of a crystal (3pF) but other capacitances over 25pF read correctly. I could add the crystal in parallel with a 25pF and got a reading of 28pF so that is one solution. Theoretically accurate to 1pF - useful.
I tried a couple of
transistors and it gave the correct pinouts and believable Hfe(gain) and
Vbe. A couple of diodes gave good readings too. It gave Vf as 529mV and
502mV at 12uA so I can use it for diode matching for ring mixers.
The other (untested) features stated in the manual are that it can measure Zener diodes and LEDs (zeners up to 4.5V only)
The unit can also accurately measure audio frequencies (up to 33kHz) and also generate frequencies up to 2MHz these are square waves though. You can also generate a PWM signal and vary the mark to space ratio, this is at a fixed frequency of around 7kHz – a pity this can’t be used to test RC servos.
The unit can also test digital sensors and remote
control! You’d need to read the manual to do this. There is a 4 page
manual available on the net but the mikrocontroller site had a 140 page
manual that should allow rebuilding the firmware – they talk about
capacitor measurements of under 100pF
to 0.01pF accuracy, time will tell if I can get that going.
In the meantime, I recommend this product for a general purpose component tester.
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