A few weeks ago I was inspired by
VK2ZAY's LC Test Oscillator video and wanted to build one of my own. So I jumped on ebay and bought a handful of J310 N-channel JFETs and started up LTSPICE to get a circuit sketched up.
The circuit simulated well and I jumped into prototyping.
Well long story short I couldn't get it working, so I started to suspect the inductors and caps I was using. The caps were el cheapo ebay bought parts and were shipped from Thailand, so I had little confidence they would hold up at 50MHz, also the inductors I was using weren't really suited for RF frequencies so I hand-wound my own aircore inductor.
In the heat of debugging I decided I needed an LCR Meter to check out some of these components, so I went on to ebay and bought a Vichy DM4070 LCR Meter for $37.... I know this is an el cheapo ebay meter, but for home use it looked good. I have been pretty happy with it so far. It is not auto-ranging, but offers an adjustment pot to dial out any stray capacitance. It is well put together and looks sharp, which doesn't hurt :)
Upon tearing it open the first thing I noticed was the large amount of manual adjustment pots. Most of the higher priced LCR meters have a bit more of software calibration in them and don't have near as many pots as this one has.
There isn't a whole lot of protection circuitry; just some clamping diodes and a single varistor.... so don't be hooking up large voltages to this meter or smoke will come billowing out.
Not a lot to it, just a lot of passives, Analog Switches and Mux ICs. All the magic is under that epoxy blob, which is probably the Micro with internal ADC.
Now that I am armed with an LCR Meter hopefully I'll get that Oscillator up and running soon........
When I see lots of passives and simple looking circuitry like this, I want to reverse-engineer it and create the schematic! I don't know where does this keen eager coming from :)
ReplyDeleteDid you find the IC used in this meter ?
ReplyDeleteThanks for the teardown
Sincerely, I'm looking for an LCR meter by meter eby and saw this, excuse a question after having disassembled and analyzed as recommended, I can measure small capacity condensdores eg 15 peaks, thank you very much for your attention
ReplyDeleteThat IC is not a micro, it is just an adc with 7 segment lcd output, invented in the 80's.
ReplyDeleteICL7106 or ICL7136 are the candidates for "the blob".
Can you extract the schematics form that?
I suspect it's all analog electronics, basically it should have an oscillator, a peak detector, an ac precision rectifier (RMS converter) and some adjacent parts for range division.
Schematics are very useful.
Nice one! I've seen some awesome LCR meters there too: http://www.directindustry.com/industrial-manufacturer/lcr-meter-84863.html
ReplyDeleteDo you still use the meter?
ReplyDelete