Bob Parker ESR meter questions - Page 1
Forum section: electronics / beginners

author: backd00r
author_rank: Contributor
timestamp: October 18, 2015, 11:53:41 pm
content: Hi, I am going through the bob parker esr meter design trying to understand it and eventually try to redesign it to my likings as a electronic learning project. first of all I dont understand the fact that this can work as anon circuitESR meter. I understand that the voltage used is low enough to not bias any transistors in the circuit but how can this device read esr of one cap when you have a bunch in parallel?. Also Why does he use BJTs throughout his original design especially for the Upro switching circuitry instead of MOSFETS. Aren't FETs better since they are voltage driven ?Thank you fellow EEVblogers.

author: backd00r
author_rank: Contributor
timestamp: October 19, 2015, 12:41:48 am
content: Hi Wilfred,Thanks for your reply. I have seen Dave use it in numerous videos and I kept wondering in sophisticated boards as a motherboard for instance how would you know if a cap is in parallel with another one?? I think it would be very hard as boards like that have multi layers and complicated stuff. Is there a new design available that avoids this issue ?? . Also I was thinking about using a PIC and a Hitachi display, because I have a couple of them laying around my lab. I guess it made sense to use BJTs 20 years ago but I think FETs would be better for this design.Thank you

author: w2aew
author_rank: Super Contributor
timestamp: October 19, 2015, 12:51:22 am
content: Quote from: backd00r on October 19, 2015, 12:41:48 amWithout seeing the design, I can't say for sure - but BJTs have a higher transconductance than MOSFETs and the design might be taking advantage of that. That may be part of the reason BJTs were used.

author: backd00r
author_rank: Contributor
timestamp: October 19, 2015, 01:48:57 am
content: I am glad you pointed that out W2aew I forgot that part of electronics. I should keep The BJTS used for the 20 gain amplifier stage (Q7,Q8) used in the ESR design since bjts have a higher Gm and can achieve better gain than FETs in general. For the switching circuitry FETs are better and can be smaller than BJTs so I can save a little real estate during the board design stage. The schematics I am refering to is attached to the following link. Please correct me if anything I am saying is wrong.http://www.flippers.com/pdfs/BlueESR.pdfThanksPS: Now you got me thinking about transconductance again can you remind me please why is it important to have a high Gm than a low Gm ?

author: Shock
author_rank: Super Contributor
timestamp: October 19, 2015, 03:09:02 am
content: Bob Parkers Zilog firmware is not public but you can get a good idea on operation from reading the two parts of the 2004 Silicon chip articles, the Dick Smith Kit K7204 and K7014 (it was first called the Genie btw). The EVB, Altronics and Blue ESR kits are pretty much the same thing (still currently being sold). You may also want to read Zilog design concepts AN004901 which has article Bob wrote on the design.Some of the contentious issues around ESR meters are:The measurement frequency, the measurement signal, the amount of input protection (and how it affects accuracy), if you use a digital or analog display (how many digits, or no display at all), if any kind of accuracy is really needed (2/4 wire measurements), shorted or erroneous low ESR cap detection (or DC resistance checking), dual purpose (display capacitance or measure accurate milliohms), support for guarded measurements (perhaps).There of course is nothing wrong with the design, just many other design positives and negatives to consider and weigh up if it's still worth working on that meter.Before you start I would read PA4TIM's websitehttp://www.pa4tim.nl/as he has done quite a lot of experimentation, he is a user here as well.Don't forget the $20 Chinese ESR meters (clone of the AVR TransitorTester project) the $50 MESR-100 and the $85 DER EE DE-5000 LCR meter (which is multi function and multi frequency) these I consider to have the best bang for buck.There is also a plethora of different designs around including a project that was recently started on the forums.https://www.eevblog.com/forum/projects/esr-meter-adapter-design-and-construction/