Turning ESR meter's coil meter into 7 seg .

Discussion in 'The Projects Forum' started by LETITROLL, Feb 7, 2014.


    Thread Starter Member

    Oct 9, 2013
    Hi every one here

    So what i want to do is actually enhance an ESR meter by changing the coil meter display witch is a 100 uA one into a digital 7 seg display .
    Am looking for a way to make this work , feel free share your Ideas , and don't forget to check the PDF file attached bellow .
    Last edited: Feb 7, 2014
  2. crutschow


    Mar 14, 2008
    The easiest is to add an A/D converter, such as this which directly drives an LCD or LED 7-segment display.
  3. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    What about choosing a better design that already has it ????
  4. takao21203

    AAC Fanatic!

    Apr 28, 2012
    1980s technology. there are not so many such A/D converters, most popular are these Intersil 40 pin ICs.

    However, you have to care about common anode/cathode, and the right LCD might be expensive.

    It may cost you 20 dollar or more just for components.


    Simple Op Amp + 44 pin Microcontroller + direct drive at 3 volts. It can run from a button cell for quite a long while.

    It is really much easier for parts count.

    Recently I have gone so far to solder one sidee of the displays directly into SMD adapter pins- only half the wires.

    If you compare that to a digital counter home etched PCB with 7segs and decoders I made 15 years ago... Took me a month or so.

    Alternative 2:

    buy an official dev. board with display on it- original MGF branded from 20 dollars or so, can be less but can be 40 dollar.

    Chinese clones / derivates can be cheaper.

    Advantage: much less assembly work.

    If you can get the display cheap + matching A/D drive with chip, it can be good for some purposes.

    For a meter like this one maybe you only need a small 3digit LED display. Or a bargraph perhaps?
  5. bertus


    Apr 5, 2008

    Thread Starter Member

    Oct 9, 2013
    I have found a lot of designs but they require a preprogrammed IC , for this one i have all the components , all i need now is using a 3 * 7 seg digits to display the value , I have an AD7816 available and also a CEMOS 7 seg decoder .
  7. takao21203

    AAC Fanatic!

    Apr 28, 2012
    these LED modules are multiplexed, and there are many different pinouts.

    Can you flash PICs?

    Actually I am, after some years dealing with this stuff, still refining my C source codes for 7seg.

    I have many working ones.

    But their problem is, it is pain to adapt them to different LED modules.

    Only very recently I programmed a new approach.

    Table 1: Anodes pin numbers/or cathodes (ascending logically)
    Table 2: segments pin numbers (ascending logicaly)

    (numbers on the LED module itself from the datasheet)

    Table 3: standard for 7seg modules

    Table 4: PORTs in array in the order how the display is soldered to the PIC
    Table 5: Bit values precomputed
    Table 6 Bit values for reset

    Code to set all the tristate
    Code to update each refresh phase.


    What is the sense of all that?

    Some day, I hope to offer a LED display module with serial port, which can read external EEPROM for the configuration tables.

    So, once the data is known and created, it can be plugged in or soldered on a pad, and the circuit will work with any display, without modification or reprogramming,

    It is still a long way to go, but I made progress, I am getting there.

    I do have some serial moduiles, but they are not so good, they need an extra controller.


    What OP would need is a controller with A/D port, and a LED display.

    I always wanted to create such a PCB, made numerous prototypes, but so far, neve produced one.

    If OP has a PIC FLASH writer, I can put the source, and tell the display used. But the trouble here is they still need to be connected in the right order. This is too much effort.

    doing these displays properly so they are easy to use is a lot of effort.

    The first few times I did 7seg. tables for PICs it always took me hours...


    Soon I relase a PIC32 PCB with a small OLED and yes it will have serial port with LED emulation, and A/D.

    It won't be so expensive but it will have some cost.

    Maybe the Intersil chip is good to use, until something better is easily available (especially, not dealing with microcontroller firmware).

    Only thing is, they dont support multiplexed LED so you have to connect a lot of wires.

    V. What about a ready-made panel meter? For 30 volts, they only cost 2 or 3 dollars. Maybe you can find one for lower voltage on eBay.

    use an OpAmp to stretch the voltage swing- it is not that hard.

    I propose that for solution
  8. debe

    AAC Fanatic!

    Sep 21, 2010
    The scale on the analogue meter type ESR is not linear. How will this go using a digital display? This is fine for a meter using a programed chip with display.

    Thread Starter Member

    Oct 9, 2013
    Hi TAKAO , seems like you have experience on A/D conversion , Can i use a 500 V ac analog panel meter instead of the 100 uA one , if so how can i interface it ?

    The analog can be converted to digital using an A/D IC , the problem is how to make the leds to display content as accurate as an analog panel ?
    Last edited: Feb 7, 2014

    Active Member

    Jan 20, 2014
  11. takao21203

    AAC Fanatic!

    Apr 28, 2012
    This more than questionable. Since the panel has 30.00 volt

    The analoguae meter is measuring current at neglible voltage.
    Not only is current to voltage converter and amplifier to 30 volts not easy to do without higher voltage rail, also the display would be fixed to 30.00 max.

    to OP yes I have used A/D a few times and I have built some simple OpAmp ccircuits from schem.

    But now these days I do almost digital stuff only.

    ESR is a parameter which must be scaled correctly, if the meter just has 99.99 it is also not helpful, even if you can remove the voltage divider somehow.

    Sorry for my suggestion I was wrong.

    In your case I'd suggest an Intersil IC + a 3 1/2 digit LCD. If you can use Element 14 they have small 3 digit LCDs and you can do the 1 with a LED.

    You also need a decade switch maybe- i don't know what values of ESR you want to display.

    Better would be to use a microcontroller PCB and some evalution demo boards have LED or LCD and A/D.

    ST has one for low price (STM8), there are some for PICs and 8051 from China for quite a discount.

    40 dollars or so for an original MFG demo board is a lot just for a meter but maybe it is useful,

    Active Member

    Jan 20, 2014
    You forget: And adjustable.
    Also there is dousins of such intersil-voltmeters that would work just fine here.
    Also the output of the ESR-project seems to be tunable.

    Also it is possible to replace the "913" resistor on this meters input to a more suitable one, to accomodate the range needed.

    A little imagination and tweaking is all that there is to it all :D
  13. takao21203

    AAC Fanatic!

    Apr 28, 2012
    Yes you can do that, however, the max. voltage determined by the new value will result in a 30.00 display

    If a ESR display value of 00.00 to 30.00 is OK for OP, then it's fine.
    Besides patching SMD with unknown schematic/part is messy.

    Thread Starter Member

    Oct 9, 2013
    This could sound stupid , but can i use an ohm meter to see the ESR resistance on the meter connetors avoiding all this headack ??

    Active Member

    Jan 20, 2014
    the dot is easy to move.

    0-3000 is good enough I think.
  16. takao21203

    AAC Fanatic!

    Apr 28, 2012
    Hmm. Maybe a microcontroller-only solution is possible for the whole meter.

    What about sampling a waveform with 1MHz chip A/D, and display a level line on 128x32 pixels OLED?

    As far as I read from the pdf, it is sending a very low voltage, high frequency signal through the cap, and then catching the response, and produce a current through the magneto mea.

    Some day I sell this as kit, as blank PCB, or with codes.

    then you can ditch the cobbling and worrying.