AFE4400 RED Data and IR Data are always as 2097151

Di Jiao

Intellectual 815 points

Other Parts Discussed in Thread: AFE4400SPO2EVM, AFE4400, TMS320F28069, AFE4490

Hi,

I am a student and want to make a pulsoximeter and meet some difficulty.

I make the AFE4400 board myself because the AFE4400SPO2EVM board is expressive for me.

I use the DCM03 as the sensor and the MCU is TMS320F28069 which I am familiar with.

I put the schematic and my project as the attachment.

I refer to the AFE4400SPO2EVM board in both schematic and codes.

What I have complete:

1.The SPI module can work and I try to write and read back the registers and the values are correct;

2.After initialization, I measure the voltage on some pins:

a) 0.494V on TX_REF pin (pin#9)

b) 0.966V on BG pin (pin#7)

c) 0.886V on VCM pin (pin#4)

But I think the TX_REF should be 0.75v.

I notice that if I don't write to the CONTROL2 (Address = 23h, Reset Value = 0000h)register with 0x020100(0000 0010 0000 0001 0000 0000) then the TX_REF voltage will be 0.75v.

Why?

3.After initialization, I try to read back some values:

	   AFE44xx_SPO2_Data_buf[0] = AFE44x0_Reg_Read(42);  //read RED Data
	   AFE44xx_SPO2_Data_buf[1] = AFE44x0_Reg_Read(43);  //read Ambient data
	   AFE44xx_SPO2_Data_buf[2] = AFE44x0_Reg_Read(44);  //read IR Data
	   AFE44xx_SPO2_Data_buf[3] = AFE44x0_Reg_Read(45);  //read Ambient Data
	   AFE44xx_SPO2_Data_buf[4] = AFE44x0_Reg_Read(46);  //read RED - Ambient Data
	   AFE44xx_SPO2_Data_buf[5] = AFE44x0_Reg_Read(47);  //read IR - Ambient Data

When my finger is NOT on the DCM03, the values are shown below:

When my finger is on the DCM03, the values are shown below:

As you see, the RED Data and IR Data are always as 2097151.

Why?

4.The initialization codes:

The code example for the AFE4400SPO2EVM board is for AFE4490 so I change some codes.

/**********************************************************************************************************
*	        AFE44xx default Initialization          				                  					  *
**********************************************************************************************************/

void AFE44xx_Default_Reg_Init(void)
{
  Disable_AFE44x0_SPI_Read();
  
  //Pulse Repetition Period Count Register:399999
  AFE44x0_Reg_Write((unsigned char)PRPCOUNT, (unsigned long)PRP);

  //Sample LED2 Start Count Register:30080
  AFE44x0_Reg_Write((unsigned char)LED2STC, (unsigned long)LED2STC_VAL);
  //Sample LED2 End Count Register:37998
  AFE44x0_Reg_Write((unsigned char)LED2ENDC, (unsigned long)LED2ENDC_VAL);
  //LED2 LED Start Count Register:30000
  AFE44x0_Reg_Write((unsigned char)LED2LEDSTC, (unsigned long)LED2LEDSTC_VAL);
  //LED2 LED End Count Register:37999
  AFE44x0_Reg_Write((unsigned char)LED2LEDENDC, (unsigned long)LED2LEDENDC_VAL);

  //Sample Ambient LED2 Start Count Register:80
  AFE44x0_Reg_Write((unsigned char)ALED2STC, (unsigned long)ALED2STC_VAL);
  //Sample Ambient LED2 End Count Register:7998
  AFE44x0_Reg_Write((unsigned char)ALED2ENDC, (unsigned long)ALED2ENDC_VAL);

  //Sample LED1 Start Count Register:10080
  AFE44x0_Reg_Write((unsigned char)LED1STC, (unsigned long)LED1STC_VAL);
  //Sample LED1 End Count Register:17998
  AFE44x0_Reg_Write((unsigned char)LED1ENDC, (unsigned long)LED1ENDC_VAL);
  //LED1 LED Start Count Register:10000
  AFE44x0_Reg_Write((unsigned char)LED1LEDSTC, (unsigned long)LED1LEDSTC_VAL);
  //LED1 LED End Count Register:17999
  AFE44x0_Reg_Write((unsigned char)LED1LEDENDC, (unsigned long)LED1LEDENDC_VAL);

  //Sample Ambient LED1 Start Count Register:20080
  AFE44x0_Reg_Write((unsigned char)ALED1STC, (unsigned long)ALED1STC_VAL);
  //Sample Ambient LED1 End Count Register:27998
  AFE44x0_Reg_Write((unsigned char)ALED1ENDC, (unsigned long)ALED1ENDC_VAL);

  //LED2 Convert Start Count Register:6
  AFE44x0_Reg_Write((unsigned char)LED2CONVST, (unsigned long)LED2CONVST_VAL);
  //LED2 Convert End Count Register:9999
  AFE44x0_Reg_Write((unsigned char)LED2CONVEND, (unsigned long)LED2CONVEND_VAL);

  //LED2 Ambient Convert Start Count Register:10006
  AFE44x0_Reg_Write((unsigned char)ALED2CONVST, (unsigned long)ALED2CONVST_VAL);
  //LED2 Ambient Convert End Count Register:19999
  AFE44x0_Reg_Write((unsigned char)ALED2CONVEND, (unsigned long)ALED2CONVEND_VAL);

  //LED1 Convert Start Count Register:20006
  AFE44x0_Reg_Write((unsigned char)LED1CONVST, (unsigned long)LED1CONVST_VAL);
  //LED1 Convert End Count Register:29999
  AFE44x0_Reg_Write((unsigned char)LED1CONVEND, (unsigned long)LED1CONVEND_VAL);

  //LED1 Ambient Convert Start Count Register:30006
  AFE44x0_Reg_Write((unsigned char)ALED1CONVST, (unsigned long)ALED1CONVST_VAL);
  //LED1 Ambient Convert End Count Register:39999
  AFE44x0_Reg_Write((unsigned char)ALED1CONVEND, (unsigned long)ALED1CONVEND_VAL);

  //ADC Reset 0 Start Count Register:0
  AFE44x0_Reg_Write((unsigned char)ADCRSTSTCT0, (unsigned long)ADCRSTSTCT0_VAL);
  //ADC Reset 0 End Count Register:5
  AFE44x0_Reg_Write((unsigned char)ADCRSTENDCT0, (unsigned long)ADCRSTENDCT0_VAL);

  //ADC Reset 1 Start Count Register:10000
  AFE44x0_Reg_Write((unsigned char)ADCRSTSTCT1, (unsigned long)ADCRSTSTCT1_VAL);
  //ADC Reset 1 End Count Register:10005
  AFE44x0_Reg_Write((unsigned char)ADCRSTENDCT1, (unsigned long)ADCRSTENDCT1_VAL);

  //ADC Reset 2 Start Count Register:20000
  AFE44x0_Reg_Write((unsigned char)ADCRSTSTCT2, (unsigned long)ADCRSTSTCT2_VAL);
  //ADC Reset 2 End Count Register:20005
  AFE44x0_Reg_Write((unsigned char)ADCRSTENDCT2, (unsigned long)ADCRSTENDCT2_VAL);

  //ADC Reset 3 Start Count Register:30000
  AFE44x0_Reg_Write((unsigned char)ADCRSTSTCT3, (unsigned long)ADCRSTSTCT3_VAL);
  //ADC Reset 3 End Count Register:30005
  AFE44x0_Reg_Write((unsigned char)ADCRSTENDCT3, (unsigned long)ADCRSTENDCT3_VAL);
  
  //Control Register 0:0
  AFE44x0_Reg_Write((unsigned char)CONTROL0, AFE44xx_Current_Register_Settings[0]);            //0x00

  //Control Register 2:TX_REF_1 + RST_CLK_ON_PD_ALM_PIN_DISABLE +
  //ADC_BYP_DISABLE + TXBRGMOD_H_BRIDGE + DIGOUT_TRISTATE_DISABLE + XTAL_ENABLE
  //+ EN_FAST_DIAG + PDN_TX_OFF + PDN_RX_OFF + PDN_AFE_OFF)
  //0000 0010 0000 0001 0000 0000 = 0x020100
  //AFE44x0_Reg_Write((unsigned char)CONTROL2, AFE44xx_Current_Register_Settings[35]);           //0x23
  AFE44x0_Reg_Write((unsigned char)CONTROL2, 0x020100);

  //Transimpedance Amplifier Gain Setting Register
  AFE44x0_Reg_Write((unsigned char)TIAGAIN, AFE44xx_Current_Register_Settings[32]);            //0x20

  //Transimpedance Amplifier and Ambient Cancellation Stage Gain Register
  //AMBDAC_0uA + FLTRCNRSEL_500HZ + STAGE2EN_LED2 + STG2GAIN_LED2_0DB + CF_LED2_5P + RF_LED2_1M
  AFE44x0_Reg_Write((unsigned char)TIA_AMB_GAIN, AFE44xx_Current_Register_Settings[33]);       //0x21

  //LED Control Register
  //LEDCNTRL_VAL,0x011414, 0000 0001 0001   0100 0001 0100, 3.9mA
  AFE44x0_Reg_Write((unsigned char)LEDCNTRL, AFE44xx_Current_Register_Settings[34]);           //0x22

  //LEDCNTRL_VAL,0x107
  AFE44x0_Reg_Write((unsigned char)CONTROL1, AFE44xx_Current_Register_Settings[30]);           //0x1E
  
  Enable_AFE44x0_SPI_Read();
}

/**********************************************************************************************************
*	        AFE44xx_Read_All_Regs          				                  					  *
**********************************************************************************************************/

void AFE44xx_Read_All_Regs(unsigned long AFE44xxeg_buf[])
{
  unsigned char Regs_i;
  for ( Regs_i = 1; Regs_i < 50; Regs_i++)
  {
    AFE44xxeg_buf[Regs_i] = AFE44x0_Reg_Read(Regs_i);
  }
}
/*********************************************************************************************************/
/**********************************************************************************************************
*	        AFE44xx_PowerOn_Init          				                  					  			  *
***********************************************************************************************************/
void AFE44xx_PowerOn_Init(void)
{
  volatile unsigned short Init_i, j;
  Init_AFE44xx_Resource();
  for (j = 0; j < DELAY_COUNT; j++)
  {
    for ( Init_i =0; Init_i < 20000; Init_i++);
    for ( Init_i =0; Init_i < 20000; Init_i++);
    for ( Init_i =0; Init_i < 20000; Init_i++);
  }
  Init_AFE44xx_DRDY_Interrupt();
  AFE44xx_Default_Reg_Init();
}

I put the schematic and my project as the attachment.

I don't know it's a hardware problem or a software problem.

I really need your kind help.

Sorry for my poor English.

I am looking forward for your help.

thanks and regards

0880.Z_F28069_PulsoximeterV4.rar

Pulsoximeter_v4.PDF

over 10 years ago

0 Praveen Aroul over 10 years ago

TI__Mastermind 49956 points

Hello Di Jiao,

It seems like the gain setting of 1M is high that it is saturating the signal at the output of the TIA.
DCM03 has a larger area photodiode and a larger area photodiode results in a higher signal current.
Higher signal current with 1M gain is saturating the signal chain.

You may want to reduce the TIA gain like 50K to begin with.

Please refer to the application section of the AFE4400 datasheet as to where to set the target dc voltage at the ADC input.

0 Di Jiao over 10 years ago in reply to Praveen Aroul

Intellectual 815 points

Hi Aroul,

Thanks for your kind help.

I take your suggestion and tried to test the AFE4400.

I have several questions and I really hope you would take a look.

1.I am not sure is there something wrong with my hardware.

Can you take a look at the schematic as the Pulsoximeter_v4.PDF.

2.I have read several topics of yours and measure the voltage on some pins:

a) 0.494V on TX_REF pin (pin#9)

b) 0.966V on BG pin (pin#7)

c) 0.886V on VCM pin (pin#4)

But I think the TX_REF should be 0.75v.

I notice that if I don't write to the CONTROL2 (Address = 23h, Reset Value = 0000h)register with 0x020100(0000 0010 0000 0001 0000 0000) then the TX_REF voltage will be 0.75v.

Is there something wrong?

3.I gain setting from 1M to 50K and I find read IR Data can vary.

And I remove it's DC component roughly and show the signal on the OLED and I think I have got the correct signal.

4.But the RED Data remains 2097151. I don't know why.

5.Because I made the hardware myself and not sure it is correct.

So I want to make sure the hardware is no problem then I will try to do the software.

Thanks again for your kind help.

Best wishes,

-Di

0 Di Jiao over 10 years ago in reply to Praveen Aroul

Intellectual 815 points

Aroul,
In the AFE4400 datasheet 8.3.5:The transmitter section uses an internal
0.5-V reference voltage for operation. This reference voltage is available on the REF_TX pin and must be
decoupled to ground with a 2.2-μF capacitor.

0 Di Jiao over 10 years ago in reply to Praveen Aroul

Intellectual 815 points

Aroul,
Thanks for your kind help and I take your suggestion and have gotten some datas which may be correct.
Could you please give me some kind advice again?
My question is shown upon.
Best regards,
-Di

0 Praveen Aroul over 10 years ago in reply to Di Jiao

TI__Mastermind 49956 points

Hello Di,

Yes you are right.
After initialization, the TX_REF pin will read 0.5V.

Data converters

Data converters forum

AFE4400 RED Data and IR Data are always as 2097151