We like to have the customers contact us, so we don't post pricing or manuals. Often the product in question isn't really what they need, and we can chat them up about their actual application, and something else may happen. I've gotten megabucks of business from situations like that.
Dean: We want to use your V680 to measure tach signals.
Me: That won't work very well.
Dean: WHAT?!!!
Me: But explain your problem and we'll build exactly what you need.
Dean: WHAT?!!!
This isn't a shopping-cart sort of product anyhow. We don't really want to sell onesies of this one, we want OEM business.
It's in regular production, automated test, the whole bit.
Remembering that any shunting impedances can upset the veracity of any particular in-circuit reading. When you don't get the result you are hoping for you have to disconnect the cap under test anyway, just to be sure.
Hmm... wouldn't replacing the spring on the far-too-weak-spring clips be easier?
I have one of these:
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...and it works pretty well. It's not specifically designed for ESR, though -- it's a general-purpose impedance meter at a half-dozen or so frequencies.
Excuse me for butting in to this very interesting discussion!
I made some Kelvin clips from a pair of small (30mm) croc clips some time ago. I filed off the teeth at the front and epoxied a strip of gold plated pcb into the body at each side of the jaw. The pcb strips came from an old, dead computer PCI card edge connector. I found that the width of the gold plated bit a perfect fit inside the jaw. I also used stereo headphone cable for the leads. Soldering the screen to the body of the croc clip.
Thanks for the mention. Nice bit of kit. I've just bought one!. Past few months I've been drooling over a 500 euro, Chinese LCR but couldn't honestly justify it work wise. This cheap unit fits the bill. Next on the list is some kind of PC controllable network analyser :)
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Hey, John, did you happen to look at applying the AD5933 in this kind of application? It's not a super good fit perhaps, but a lot of stuff in 16 pins for the dollars.
Best regards, Spehro Pefhany
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"it\'s the network..." "The Journey is the reward"
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That certainly gets close. The claimed impedance range is 100r to 10M, so it would need some help to do esr. But a similar home-made thing could be done with a cheap FPGA and a cheap ADC and DAC, and some analog glue... synthesize a variable-freq sine wave and digitize the I and Q parts of the component response.
A very sophisticated swept-frequency impedance meter could be built for peanuts. It would just take a lot of engineering, and that mostly firmware.
We've been making our own DDS products lately, with just an FPGA and some DACs. It ain't hard any more. Here's one,
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which uses a Spartan3 and four dual 125 MHz, 14-bit dacs. The waveform tables are in ram, so later on we can do arbs, too. Even just a uP and a dac can replace an analog oscillator these days, and do lots more tricks.
It's a bit on the weak side, but the real problem is that it's got a smooth flat surface that can't grip and slides right off. Making the spring stronger simply seems to make it "spring" off. Note, this clip is used on one of the very expensive HP Agilent four-coax probe sets.
Are you referring to their Kelvin clip, what's the link?
OK, we have a company-standard rom-builder program that gobbles up S28-format uP code and Xilinx .RBT files and builds binary rom images, sort of a barbaric linker. I modified it to accept a /RLL switch, to do essentially the same thing as your code (but recoded it in PowerBasic!) It's byte oriented, and whenever I see a 0 byte, I output it and count the total number of 0's in the run, then poke that count into the next output byte. A single input 0 then becomes two bytes (0,1) and a run of 100 zeroes becomes two bytes, (0,100). Nonzero bytes just get shipped out unchanged.
I added 32 extra zero bits at the end (0,4) because the chips seem to like that, and then (0,0) as the end-of-file marker, to tell the uP config code when to quit. We also added a /FILL switch to load unused image bytes with all 1's, to make eprom programming a bit faster.
A relatively simple VME interface chip, an XC3S200, crunches to 0.23 of the original size, over 4:1 compression.
A fairly hairy 8-channel massively pipelined DDS synthesizer in an XC3S1500, using lots of resources, compresses to 0.43. If we initialize the block rams, it's more like 0.46.
We could also RLL the 0xFF bytes, but that would help only marginally. We have come up with some trickier dictionary-based algorithms, but the RLL ratios are much better then we need at present, so we'll just go with this.
Runtime unpacking and config bit-banging should be fast. When we see a null byte, we can hop to a brute-force routine that reads the next byte and bangs out up to 2040 zero bits as fast as it can wigwag the CCLK port bit. It should be much faster than the old loop, which just shifted all the data bits out.
And add an emitter resistor on the voltage regulator transistor so there's a path for the current to take.
It's not a bug, it's a feature ;-). As it is now, there's not enough current through the junkbox LED (voltage reference) to light it up, so having the meter off zero is the Power On indicator.
As I remember, it draws about 6 mA. I need to go back and read Thompson's threads about CMOS oscillators and overloading the input diodes and see if it could get a little lower. Or use a CMOS 555.
This was done in response to downloading the Creative ESR meter schematic and seeing that it drew 100 mA or something stupid like that. IMHO, it's comparable in performance (0-30 ohm), but a whole lot less parts and power consumption.
Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
That list of requirements is satisfied nicely by Bob Parker's ESR meter. There isn't much point re-inventing that one so people might as well concentrate on the fancier list of specs below.
One other feature: Should work even if one side of the capacitor is already grounded. E.g. should be able to measure the input impedance of a pin of a complicated IC with respect to ground, even when the IC is soldered down to a board, and with the IC ground connected to the ground of all sorts of test equipment, power supplies etc. Lots of fancy impedance analysers assume that components are always floating, which makes them useless in a lot of situations.
have built about a dozen Dick Smith ESR meter kits and found the instructions to be quite good but I could see how an inexperience kit builder could be somewhat overwhelmed with having to make some of the decisions... generally one would expect that if you have purchased an ESR meter kit that you would have ...
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