That would be it......... never seen that used before, live and learn.
1st line in setup.
Makes sense now...cheers.
/*
This is a program to use the MCP3424 A/D converter along with a Nano and OLED
to provide a microOhmmeter function.
This unit automatically conducts four ranges on the A/D converter and selects the proper one.
Start date is 04/18/2019
Complete date 04/20/2019
Upgraded to PCB layout, complete rework of sketch program file
Upgraded date is 07/01/2020
Upgraded to measure test current with 0.1 Ohm resistor
Upgraded date is 07/03/2020
Upgraded to read over 2 OHms 08/25/2020
Minor tweeks and a warning note
ref Gainx1, max input voltage is 2.5 VDC for full scale ***
ref Gainx8, max input voltage is 0.25 VDC for full scale **
** ref SRxxB is bit resolution, ranging from 12 to 18 bits ***
** MCP 3421 has one channel input
** MCP 3422 has two channel inputs
** MCP 3424 has four channel inputs, from CH1 to Ch4
* *************************************************************************
WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
DO NOT DO RESISTOR TESTS WITH ONLY THE USB POWER TO THE METER!!
THAT RESISTOR UNDER TEST REVERSES BIASES THE ARDUINO NANO 5 VOLT REGULATOR
AND WILL BLOW THE REGULATOR. A 6.6 VOLT POWER SUPPLY MUST BE CONNECTED
TO THE METER ANY TIME THE USB PC PORT IS PLUGGED INTO THE ARDUINO NANO
WHEN CONNECTING A TEST RESISTOR TO THE MICRO OHM METER.
* ***********************************************************************************
*/
#include <Wire.h>
#include <MCP3424.h>
#define OLED_RESET 4
#include <Adafruit_SH1106.h>
Adafruit_SH1106 display(OLED_RESET);
MCP3424 adc(PIN_FLOAT, PIN_FLOAT);
const int V_Cal = 1000; //1166 number is used to calibrate voltage
float R_Cal = 1.005; // R_CAL is the calibration of the meter against a known resistor
#if (SH1106_LCDHEIGHT != 64)
#error("Height incorrect, please fix Adafruit_SH1106.h!");
#endif
float value; //define variable
double R5_Ohm ;
float Vx_Ohm;
float Rx_Ohm;
double range1;
double range2;
double range3;
double range4;
float test_resistor;
float Ad_Cnv = 0;
int Ad_In = 0;
void setup()
{
analogReference(INTERNAL);
Serial.begin(9600);
display.begin(SH1106_SWITCHCAPVCC, 0x3C);// initialize 128/64 with the I2C addr 0x3D
display.setTextSize(3);
display.setTextColor(WHITE);
display.clearDisplay();
display.setCursor(25, 0);
display.print("uOhm");
display.setCursor(20, 30);
display.print("meter");
display.display();
delay(1000);
}
void do_R5ohm() //measure the voltage on 5 Ohm 1% resistor for calculation
{
adc.creg[CH4].bits = {GAINx8, R16B, CONTINUOUS, CH4, 1 };
ConvStatus err = adc.read(CH4, R5_Ohm); //Read 5 Ohm Volts
R5_Ohm = R5_Ohm * 10.14; //R5_Ohm variable contains voltage drop on resistor
}
void do_range1() //following routines runs variable settings on channel 3
{
adc.creg[CH3].bits = {GAINx8, R18B, CONTINUOUS, CH3, 1 };
ConvStatus err1 = adc.read(CH3, range1); //Read Rx Volts
range1 = range1 * R_Cal / R5_Ohm;
}
void do_range2()
{
adc.creg[CH3].bits = {GAINx1, R18B, CONTINUOUS, CH3, 1 };
ConvStatus err2 = adc.read(CH3, range2); //Read Rx Volts //Read Rx Volts
range2 = range2 * R_Cal / R5_Ohm;
}
void do_range3()
{
adc.creg[CH3].bits = {GAINx2, R14B, CONTINUOUS, CH3, 1 };
ConvStatus err1 = adc.read(CH3, range3); //Read Rx Volts
range3 = range3 * R_Cal / R5_Ohm;
}
void do_range4()
{
adc.creg[CH3].bits = {GAINx1, R12B, CONTINUOUS, CH3, 1 };
ConvStatus err1 = adc.read(CH3, range4); //Read Rx Volts
range4 = range4 * R_Cal / R5_Ohm;
}
void do_battvolts()
{
Ad_In = analogRead(7); //show battery voltage
Ad_Cnv = map(Ad_In, 0, 1024, 0, V_Cal); //convert to actual voltage reading
display.setCursor(50, 56);
display.setTextSize(1);
display.print("Batt V = ");
display.print(Ad_Cnv / 100, 2); //show two decimal result
display.setTextSize(2);
}
//*************************************************************************************
//main program starts here
void loop()
{
display.setTextSize(2);
display.setTextColor(WHITE);
do_R5ohm(); //run voltage on 5 ohm resistor
Serial.println (R5_Ohm, 5);
if (R5_Ohm < 0.01) //if A/D result is negative, no test resistor is connected
{
display.clearDisplay();
display.setCursor(0, 20);
display.setTextSize(4);
display.print("OPEN!");
display.display();
}
else //do the entire resistance check program
{
do_range1();
do_range2();
do_range3();
do_range4();
// Serial.print ("R5 ");
// Serial.println (R5_Ohm, DEC); //send to USB for test_resistor purposes
test_resistor = max(range1, range2); //identify the maximum resistance value
test_resistor = max(test_resistor, range3);
test_resistor = max(test_resistor, range4);
if (test_resistor > 2.0) //if over 2 ohms, show over range
{
display.clearDisplay(); //over range
display.setCursor(0, 0);
display.print("Over");
display.setCursor(0, 25);
display.print("Range");
display.display();
}
else
{
// Serial.print (" test_resistor=");
// Serial.println (test_resistor, DEC);
display.clearDisplay();
display.setCursor(80, 38);
display.print("Ohm"); //show ohms value
display.setCursor(0, 38);
display.print(test_resistor, 4);
display.setCursor(80, 19);
display.print("mOhm");
display.setCursor(0, 19);
display.display();
// Serial.println (test_resistor, DEC);
if (test_resistor * 1000 > 999) //show milliohms result for either xxxx.xx, or xxxx
{
display.print(test_resistor * 1000, 0); //show milliohms value
display.display();
}
else
{
display.print(test_resistor * 1000, 2);
display.display();
}
if (test_resistor * 1000000 < 999999) //test for maximum uOhm digit display
{
display.setCursor(80, 0); //if under 999999, display it
display.print("uOhm");
display.setCursor(0, 0);
display.print(test_resistor * 1000000, 0);
do_battvolts();
display.display();
}
else
{
display.setCursor(0, 0);
display.print(" ");
display.display();
}
}
}
}
