The "Genie" ESR Meter Review By Andy Barkley
Building a Genie
Unlike the Wizard, Bob Parker's Australian meter does not have a catchy name. The box it comes in lists the contents its "K-7204 EA 1/96 ESR & Low Ohms Meter - which is quite a mouthful. We call it the "Genie" in the workshop, and that's the name I'll use in this review.
Once opened, the box reveals another big difference between the Wizard and Genie - the latter comes in kit form! With the exception of' a 9V PP3 battery, the kit contains everything you require to build the meter. The construction notes are excellent. We built our Genie in under two hours using a soldering iron, side-cutters and screwdrivers. A variable DC supply is required to set the threshold point for the low-battery indicator accurately. In addition, if' you are a stickler for accuracy, you need a couple of resistors of known precision to calibrate the instrument, though 1 per cent devices are supplied with the kit.
Crocodile clips and 4mm plugs come with the kit. We use silicone rubber test leads fitted with needle-point probes however. In addition we've fitted four rubber feet to the box.
The Genie fits into a regular ABS hobby-type box that measures 130 x 68 x 40mm - it comes with the kit. The box's lid has been discarded in favour of a customised one. This is sprayed black and has accurately punched holes for the screws, connectors and display. A table of typical ESRs for a wide range of electrolytic capacitors is silk-screened on the lid. There are two 0.5in. seven-segment displays, a multi-function push-switch and two 4mm sockets for the test probes.
The 'custom' parts - front panel, PCB and software - are all of a very high standard. We particularly liked the milled-edge on the red Perspex display window, so that its surface fits flush with the front panel. The whole thing looks very smart, with a Heathkit-type appearance.
The Genie can be powered by an internal 9V PP3 battery or an external 9V supply. There's no connector for the latter in the kit, nor is the box drilled for a DC connector, but the instructions include details of how to modify the circuit to disable the low-battery indicator when external power is used.
We opted for battery-only operation and, as part of the calibration procedure, used our bench power supply to produce 7V to set the instrument's low-battery indicator threshold.
A single press on the push-button switches the Genie on. 'EA' is displayed momentarily, then a '-' in the lefthand seven-segment display. Short the probes together then push the button again to calibrate the unit for the test leads in use.
ESR measurement is carried out by connecting the test leads to each leg of the capacitor being tested. Its ESR is shown as two digits in the display. Although the Genie and the Wizard use quite different test signals, correlation between the two instruments is very good. We have never had a capacitor pass with one and fail with the other.
The two meters use quite different approaches to ESR measurement. With both, an HF signal is applied to the capacitor being tested. So that no semiconductor junction is turned on, the signal amplitude is below 0.6V. The Wizard uses a sinusoidal 5mV RMS test signal, carrying out its ESR measurement by analogue techniques. The test signal used by the Genie appears to consist of bursts of very short-duration pulses. Each pulse has a duration of about 7µsec, the pulses within a burst being about 500µsec apart. Digital techniques are used to perform the measurement.
The heart of the Genie is a Z86E0408 microcontroller chip, which is supplied preprogrammed with the necessary firmware. Short-duration current pulses are applied to the capacitor being tested: the resultant voltage pulses are proportional to the capacitor's ESR. After a set time interval, the pulse amplitude is compared with the voltage developed across an internal capacitor that's charged by a set constant current. Counters and comparators within the microcontroller chip perform the timing and voltage measurement.
Genie or Wizard?
After the test you leave the probes open-circuit: the Genie will switch off automatically after a few minutes. We'd love the Wizard to do this because, although its power consumption is meagre, it has no indication of being on and we've frequently discharged its batteries by forgetting to switch it off at the end of the day. Both units have a low-battery warning. The Wizard uses a single red LED for the low-battery warning. The Genie shows a 'b' in its display.
The Genie measures resistances up to 99‡, while the Wizard goes up to only 30‡ or so (on a logarithmic moving-coil meter). The Genie's extended range is of little use for ESR testing, since most of the electrolytic capacitors used in TV sets, VCRs etc. should have an ESR below 2511, but the ability to measure up to 100‡ accurately is useful when checking PCB tracks for short-circuits, dry-joints and the like. The Wizard bleeps when it measures ESR below about 1‡ - a useful feature when testing a number of capacitors on a PCB, as it means that the engineer can concentrate on the PCB without having to look at the instrument's display.
Although the Wizard has a more professional appearance than the Genie, we feel that in practice the Genie is more robust - mainly because it uses seven-segment LED displays rather than a fragile moving-coil meter. We've managed to drop both instruments. The Genie is unscathed, but the Wizard's meter cover is cracked. One comment Martin Pickering made was that he loves the Wizard's probes. We second this. They are slim, slightly flexible and never tangle - a dream to use.
Based purely on features, there's little to separate the instruments. Both will confidently indicate a high-ESR (i.e. dead) electrolytic capacitor. The Genie has one trump card however - so long as you don't mind selfassembly: while the Genie cost us a total of $71 (Australian), which at the time of writing is equivalent to about £30, the Wizard costs £169 (fully built).
Martin Pickering's review of the Wizard appeared in the June 1998 issue of Television. It provides a recap on what ESR is. Two articles in the January and April 1993
issues of Television, All about Electrolytic Capacitors and A Simple ESR Meter for Electrolytics respectively, provide a detailed analysis of ESR and a simple ESR meter design.
Bob Parker's web page is http://www.nIc.net.au/~bobp/esrmeter.htm It tells you all about him, the ESR meter, what ESR is, provides tips if you have difficulty building or using the meter, and has information on other useful items he has designed.
A newsgroup on the internet can be found at sci.electronics.repair Both ESR instruments receive frequent recommendations.
The Capacitor Wizard in the UK is sold by SatCure
The Genie ESR meter was available from Dick Smith Electronics. Fax +61 2 9805 0901. Dick Smith Electronics Pty Ltd., PO Box 321, North Ryde, Sydney, NSW 2113 Australia.
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