ESR-Meter

Some time ago I came across this design of an ESR meter. I then decided to build it, but for the display I wanted to use a pic + lcd.

My circuit:

(Clickable)

 

Pictures:

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Update 22/07/08

I made a mistake in my circuit. The non inverting inputs off the opamp should be connected to 2,5V instead of the ground. I could make a new pcb, but I decided to make it myself easy and made a special ic socket with a voltage divider build in.

The new circuit diagram:

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Update 24/02/09

I got the code working. Apparently there is a bug in picbasic that gives problem with the AD on a 16F690. Therefore I made my own code to get the analog value.

 

The code:

    Device         16F690
    Config         INTRC_OSC_NOCLKOUT, WDT_OFF, PWRTE_OFF, MCLRE_OFF
    XTAL = 8
    OSCCON = %01110111

    Dim spanning As Word
    Dim esr As Float
 
    Declare LCD_DTPIN PORTC.4
    Declare LCD_ENPIN PORTC.3
    Declare LCD_RSPIN PORTB.6
    Declare LCD_LINES 2   

    TRISA.2  = 1 
    ADCON0 = %10000001
    ANSEL  = %00000100       
    ANSELH = %00000000
    
    ADIN_RES = 10         
    ADIN_TAD = FRC           
    ADIN_STIME = 500              

    Symbol lcdTijd  = 600
    Clear
    Cls
    Print At 1, 1,  "ElektronicaStynu"
    Print At 2, 1,  " ESR-Meter V1.2 "
    DelayMS  lcdTijd
    Print At 1, 1,  "lektronicaStynus"
    DelayMS  lcdTijd
    Print At 1, 1,  "ektronicaStynus."
    DelayMS  lcdTijd
    Print At 1, 1,  "ktronicaStynus.b"
    DelayMS  lcdTijd
    Print At 1, 1,  "tronicaStynus.be"
    DelayMS  lcdTijd
    
    Cls
    Print At 1,  1,  " ESR-Meter V1.2 "  
    Print At 2,  1,  "  ESR =   ,     "
    Print At 2, 16, $FE,$40,$00,$0E,$11,$11,$11,$0A,$1B,$00



While 1 = 1 
    GoSub AD_in
    spanning = spanning - 480
    esr = spanning  / 19
    If esr > 27 Then
        Print At 2, 9, "Open       "
    Else 
        Print At 2, 9, DEC2 esr , "         "
    EndIf
    DelayMS 550    


Wend
AD_in:
    ADCON0 = %10001001    
    DelayMS 510
    ADCON0.1 = 1 
    While  ADCON0.1 = 1 : Wend
    spanning = 0
    spanning.HighByte = ADRESH
    spanning.LowByte = ADRESL


Return
End

The hex file

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Update 26/03/2011

There was another adaptation on the pcb that was not in the circuit diagram above.

The LCD has to be connected differently. I don't know why anymore, but here is the new circuit diagram:

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