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ESR Meter Adapter Design and Construction

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I am going to share the design and construction of an ESR Meter adapter design and construction. The plan is to end up with a design that is similar in appearance to Dave's ucurrent that will allow a DMM to be used as an ESR meter. At this point in time I have not built the circuit.

The requirements are:

* To have a simple design that can be constructed on a single-sided circuit board.
* Operates at 100kHz.
* Be a true ESR meter as oppose to an impedance meter.
* Work in either the 2-Wire or 4-Wire mode.
* Be well protected from charged capacitors and applied voltages.
I will be using LTspice to verify the design goals.

Simulation Basic Functionality

This the LTspice model configured for normal operation. U3 is configured as a 100 kHz square wave oscillator. 1/3 of a CD74HC4053 analog Mux / Demux  is used to provide a current to the capacitor under test through R3, R9 and C5. The voltage across the capacitor under test is sensed via R5 and C5. Another 1/3 of the CD74HC4053 is used as a synchronous detector. U4 provide gain, resulting in a scale of 1V=10 Ohms.
R16 and R17 are included in the model to explore the effect of lead resistance.

If I plot Vout versus ESR, I get:

Simulation of a Charged Capacitor

I wanted to make sure that the adapter is not damaged if it is connected to a charged capacitor. To demonstrate this a switch is used to connect the adapter to a charged capacitor, the charged capacitor is connected at t=2ms:


After a very brief transient the meter actual reads the correct value of ESR.

There is a brief impulse of current in R9. A special 'pulse withstanding' resistor will be selected for the R9 location.

Application of Line Voltage

Although not recommended, it would be nice to know that the adapter will survive being connected across the line. In this test 240V ac at 60 Hz is applied to the input.

Results of applying line voltage

The upper trace shows the dissipation in R5. (930uW average power)
The middle trace shows the dissipation in R9. (18.6mW average power)
The lower trace is the line voltage across the terminals of the adapter.

Real Schematic

This is the real schematic. It is very similar to the simulation schematic. The 74HC4053 has been broken up into four parts to make the schematic easier to read.

J1 and J2 are used for 2-wire measurements. J1-J4 are used for 4-wire measurements. J5 and J6 are the voltage output to the DMM.

Board Layout

Here is a picture of the board layout:

I need to add a switch for the power.

I will add more details after I have built the prototype. The LTspice models are attached if you want to play with the circuit.

Parts are on order.... to be continued....


Nice, looks like it should be easy to build as well.  :-+

Hope to see some pictures of the prototype.  Assuming it all works well, any chance of getting either a gerber of the artwork or scale PDF?  Looks like a nice project to etch and assemble, but it doesn't look like I use the same CAD package as you.

Nice work. Keep it up.

Nice design. Have you considered that the 4053 is quite slow to switch on or off? At +5V supply voltage the switching time is about 0.5uS, which might cause non-linear indication at 100 KHz sampling frequency / 5 uS half period.


--- Quote from: ElectroIrradiator on December 03, 2013, 08:47:08 am ---Have you considered that the 4053 is quite slow to switch on or off? At +5V supply voltage the switching time is about 0.5uS, which might cause non-linear indication at 100 KHz sampling frequency / 5 uS half period.

--- End quote ---

Thank you for your input, this is the kind of feedback that I was hoping to get by posting my design. :-+

I have considered the delay from the select pin, to the switch opening and closing.

The 74HC4053 is about an order of magnitude faster than the CD4053 with maximum switching times of around 50ns (I checked TI and NXP).

The 74HC4053 in the source will compensate for the delays in the sense circuitry.

I will be building the circuit soon.

I am looking for a suitable enclosure. There are some advantages to keeping the board dimensions less than 100mm x 50mm, so that the board can be made cheaply at places like itead. The other requirement is that the box is deep enough to hold a 9V battery.

I have found the UB5 Jiffy Box from altronics


This the same box that was used by Dave in the uCurrent. It was also suggested by Harvs in a PM. This box seems to be Australian design and manufacture.

Does anybody know of a box like this with worldwide availability?



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