Arduino/Genuino 'Sungmod'

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Arduino/Genuino "Sungmod"

A high Voltage Power Supply for Photodiodes

The prototype

ระวัง ไฟฟ้า แรง สูง !

You have been warned ...

✈ Motivation

Some Photodiodes in our lab used for e.g. a Photon Counter need a High Voltage Bias. This design uses two identical power transformers (connected back to back) to generate a mains-isolated high voltage of approx. 300 V. This method was the preferred solution of my (now retired) colleague, Mr. Paul Studerus. So consider this design somehow as a tribute to yet another engineer with "Guru-Status", crossing my professional career.

✈ The Design

The Block Diagram of the "Sungmod"

The design is straightforward. As the dissipated power is very small, we used a linear regulator (IRF740/840). The High Voltage (approx. 300V) is generated with two identical transformers, were the low voltage side is connected back to back.

The Setpoint is generated by an AD5667R (Dual, 16-Bit nanoDACs® with 5 ppm/°C On-Chip Reference, I2C® Interface). A single Opamp (OPA140) controls the output voltage therefore, that it pulls the gate of the main transistor down. It is pulled up by a pnp transistor injecting approx. 1 mA into the gate.

The current is measured with a 1 Ω shunt. The voltage drop across it is amplified with a LT1789CS8-1 (Micropower, Single Supply Rail-to-Rail Output Instrumentation Amplifier) and then fed to an analog input of the Arduino. One could realise a current limit by that in software, but the prototype hasn't got that feature.

A look inside. And yes, the interesting components are below the ribbon cable :-)

✈ Downloads

✈ Test Sketch for Arduino/Genuino Nano

Double click on code to select ...

/* ////////////////////////////////////////////////////////////////// 
  
ARDUINO/Genuino Nano Sketch for Sungmod
https://www.changpuak.ch/electronics/Arduino-Sungmod.php
A High Voltage Power Supply for Photodiodes
Software Version 5.1
28.07.2019, Alexander Sse Frank
USEFUL:
learn.adafruit.com/adafruit-gfx-graphics-library/graphics-primitives
  
////////////////////////////////////////////////////////////////// */
 
#include <Adafruit_GFX.h>
#include <Adafruit_SH1106.h>
#include <Wire.h>
  
// DISPLAY
 
#define OLED_MOSI  11
#define OLED_CLK   12
#define OLED_DC    9
#define OLED_CS    8
#define OLED_RESET 10




Adafruit_SH1106 display(OLED_MOSI,OLED_CLK,OLED_DC,OLED_RESET,OLED_CS);
 
#if (SH1106_LCDHEIGHT != 64)
#error("Height incorrect, please fix Adafruit_SH1106.h!");
#endif

// ROTARY ENCODER

const int RotaryEncoder1 = 4 ;   // PRESSED
const int RotaryEncoder2 = 2 ;
const int RotaryEncoder3 = 3 ;

volatile bool LEFT = false ;
volatile bool RIGHT = false ;
volatile bool READY = true ;

// /////////////////////////////////////////////////////////////////////
// SUBROUTINES DAC AD5667R
// /////////////////////////////////////////////////////////////////////
 
// Pin 6 = ADDR is on GND >>> A0 = 1, A1 = 1
// Only VOUTA is used
 
const byte DAC_ADR = 0x0F ;
const float VoltFactor = 206.221 ;
const float MaxVolt = 270.000 ;
const float MinVolt = 0.000 ;
float SetVolt = 259.0 ;
 
void WriteDAC(byte cmd, unsigned int payload) 
{
  byte lsb = payload & 0xFF ;
  byte msb = (payload & 0xFF00) >> 8 ;
  Wire.beginTransmission(DAC_ADR) ;  
  Wire.write(cmd) ;   
  Wire.write(msb);  
  Wire.write(lsb);                  
  Wire.endTransmission();
}
 
void UpdateVolt() 
{
  unsigned int Setpoint = 0x0000 ;
  Setpoint = (int)(SetVolt * VoltFactor) ; 
  WriteDAC(0x10, Setpoint) ; 
  Serial.println(Setpoint,DEC) ;
}
 

 
// /////////////////////////////////////////////////////////////////////
// D I S P L A Y
// /////////////////////////////////////////////////////////////////////

float Current = 0.0 ;
const int CurrentPin = A6 ;
int CursorPos = 2 ;  
int CurrBuff[32] ;      // STORES RAW VALUE
int CurrBuffPoint = 0 ;
const int MaxCurrBuffPoint = 31 ;
const float CurrentMuly = 5.0 / 1023.0 ; 


void ReadCurrent()
{
  int CurrBuffSum = 0 ;
  
  CurrBuffPoint += 1 ;
  if(CurrBuffPoint > MaxCurrBuffPoint) CurrBuffPoint = 0 ;
  CurrBuff[CurrBuffPoint] = analogRead(CurrentPin) ;
  CurrBuffSum = 0 ;
  for(int i = 0 ; i < MaxCurrBuffPoint; i++)
  {
    CurrBuffSum += CurrBuff[i] ;
  }
  Current = CurrentMuly * (float)CurrBuffSum / MaxCurrBuffPoint ; 
  Serial.println(Current,3); 
}


void UpdateDisplay()
{
  ReadCurrent() ;
  display.clearDisplay() ;
  display.setTextSize(1) ;
  display.setTextColor(WHITE) ;
  display.setCursor(0,0); display.print("*****  SUNGMOD  *****") ;
  display.drawLine(0, 12, 128, 12, WHITE) ;

  display.setTextSize(2) ;
  // VOLTAGE
  display.setCursor(10, 21);
  if (SetVolt < 99.999) display.print(" ");
  if (SetVolt < 9.999) display.print(" ");
  display.print(SetVolt,3);
  display.setCursor(104, 21);
  display.print("V");
  // CURSOR
  display.setCursor(10, 26);
  if(CursorPos == 1) display.print(" ");
  if(CursorPos == 2) display.print("  ");
  if(CursorPos == 3) display.print("    ");
  if(CursorPos == 4) display.print("     ");
  if(CursorPos == 5) display.print("      ");
  display.print("_");
  // CURRENT
  display.setCursor(10, 45);
  if(Current < 99.999) display.print(" ") ;
  if(Current < 9.9999) display.print(" ") ;
  display.print(Current,3);  
  display.setCursor(104, 45);
  display.print("mA");
   
  display.display() ;
}



// /////////////////////////////////////////////////////////////////////
// S E T U P
// /////////////////////////////////////////////////////////////////////
 

void setup() 
{
  Serial.begin(115200);

  Wire.begin() ;

  pinMode(RotaryEncoder1, INPUT_PULLUP) ;
  pinMode(RotaryEncoder2, INPUT_PULLUP) ;
  pinMode(RotaryEncoder3, INPUT_PULLUP) ;
  
  // YELLOW
  attachInterrupt(digitalPinToInterrupt(RotaryEncoder2), 
  RotaryEncoderISR2, FALLING) ;
  // GREEN
  attachInterrupt(digitalPinToInterrupt(RotaryEncoder3), 
  RotaryEncoderISR3, FALLING) ;

  // INIT OLED
  display.begin(SH1106_SWITCHCAPVCC) ;
 
  // SHOW STARTUP SCREEN
  display.clearDisplay() ;
  display.setTextSize(1) ;
  display.setTextColor(WHITE) ;
  display.setCursor(0,0);
  display.println("*****  SUNGMOD  *****") ;
  display.drawLine(0, 12, 128, 12, WHITE) ;
  display.setTextSize(1) ;
  display.setCursor(0,21) ;
  display.println("A HIGH VOLTAGE") ;
  display.setCursor(0,33) ;
  display.println("POWER SUPPLY FOR") ;
  display.setCursor(0,45) ;
  display.println("PHOTODIODES.") ;
  display.setCursor(0,57) ;
  display.println("BUILT 23.10.2021") ;
  display.display() ;


  // DAC AD5667R
  // RESET ALL
  WriteDAC(0x28, 0x0001) ;
  // POWER UP CHANNEL A
  WriteDAC(0x20, 0x0001) ;
  // SETUP LDAC PIN = BOTH DISABLED
  WriteDAC(0x30, 0x0003) ;
  // SWITCH ON REFERENCE
  WriteDAC(0x38, 0x0001) ;

  delay(999) ;
 
  UpdateVolt() ;
  UpdateDisplay() ;
}


// /////////////////////////////////////////////////////////////////////
// M A I N 
// /////////////////////////////////////////////////////////////////////
 
void loop() 
{
  // KEY ROTATED ?
  // //////////////////////////////////
  if(LEFT)
  // //////////////////////////////////
  {
    switch (CursorPos)
    {
      case 0 : 
        if((SetVolt - 100.0) >= MinVolt) SetVolt-=100.0 ;
        break ;
      case 1 : 
        if((SetVolt - 10.0) >= MinVolt) SetVolt-=10.0 ;
        break ;
      case 2 : 
        if((SetVolt - 1.0) >= MinVolt) SetVolt-=1.0 ;
        break ;
      case 3 : 
        if((SetVolt - 0.1) >= MinVolt) SetVolt-=0.1 ;
        break ;       
    }  
    UpdateVolt() ; 
    delay(59) ;
    READY = true ;
    LEFT = false ;
    RIGHT = false ;
  }
  
  
  // //////////////////////////////////
  if(RIGHT)
  // //////////////////////////////////
  {    
    switch (CursorPos)
    {
      case 0 : 
        if((SetVolt + 100.0) <= MaxVolt) SetVolt+=100.0 ;
        break ;
      case 1 : 
        if((SetVolt + 10.0) <= MaxVolt) SetVolt+=10.0 ;
        break ;
      case 2 : 
        if((SetVolt + 1.0) <= MaxVolt) SetVolt+=1.0 ;
        break ;
      case 3 : 
        if((SetVolt + 0.1) <= MaxVolt) SetVolt+=0.1 ;
        break ;       
    }
    UpdateVolt() ;
    delay(59) ;
    READY = true ;
    LEFT = false ;
    RIGHT = false ;
  }

  
  // //////////////////////////////////
  // KEY PRESSED ?
  // //////////////////////////////////
  if(!digitalRead(RotaryEncoder1)) 
  {
  CursorPos += 1 ;
  if(CursorPos > 5) CursorPos = 0 ;
  delay(199) ;
  }    

  
  UpdateDisplay() ;
  delay(59) ;
  
  
}


// /////////////////////////////////////////////////////////////////////
// INTERRUPT SERVICE ROUTINES
// /////////////////////////////////////////////////////////////////////
  
void RotaryEncoderISR2()
{
  // YELLOW
  if(READY)
  {
  LEFT = false ;
  RIGHT = false ;
  byte autre = digitalRead(RotaryEncoder3) ;
  if (autre > 0) RIGHT = true ;
  if (autre < 1) LEFT = true ;
  }
}
  
void RotaryEncoderISR3()
{
  // GREEN
  if(READY)
  {
  LEFT = false ;
  RIGHT = false ;
  byte autre = digitalRead(RotaryEncoder2) ;
  if (autre > 0) LEFT = true ;
  if (autre < 1) RIGHT = true ;
  }
}
  
  
// /////////////////////////////////////////////////////////////////////
// END OF FILE.
// /////////////////////////////////////////////////////////////////////

✈ Performance

Voltage Drift @ 259.0 V, current drawn was 1.0 mA. First 9 hours after Power On.

A note on Arduino Nano :
We first used the Nano Every, but it turned out, that the 5 V regulator (MPM3610) was somehow unable to supply the AD5667R. Switching to the original Nano (LM1117IMPX-5.0) solved this problem. (Without redesigning the board).

✈ Share your thoughts

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Your Browser says that you allow tracking. Mayst we suggest that you check that DNT thing ?

t₁ = 6498 d

t₂ = 191 ms