## NHS3152 - Measure resitance correct param ADC-I2D-DAC

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## NHS3152 - Measure resitance correct param ADC-I2D-DAC

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Contributor III

Hello,

I am trying to create code following @driesmoors ' solution to Measure resitance: (NHS3152)

I have modified code from the example: mainndeft2t.c.

The program follows the following logic:

0. Wake up when NFC field is detected

1. Set the configuration of the analog pins to IOCON_FUNC_

2. Connect the DAC to ANA1, set a continuous conversion of 1.25V (used: adcdac_nss_example_1)

3. Connect the I2D to ANA4, configure correctly and start a conversion. Only when         a conversion is started, current will start flowing over your resistor. The current             will continue to flow when the conversion ends. -> a (used: i2d_nss_example_1)

4. Connect the ADC to ANA4, and measure the voltage. -> v4 (used: adcdac_nss_example_3)

5. Connect the ADC to ANA1, and measure the voltage. -> v1

(New insturcitons)

6. R= V(V1-V2)/(I_pico * 10^-6)

7. Display resitance value on screen phone

I connected a 100KOHM resitor between ana1 and ana4. The code runs but i am not getting a close resistor value. I get the following results:

r=100[Kohm]

adc_1 = 1.34 [V]

adc_4 = 1.04 [V]

current_picoampere = 5*10^5 [pA]

which gives a low res = 0.3/0.5= 0.6 [Ohm]

I have the following questions:

1. How do i pass 1.25V ana1? (formula to convert the bits to ana value)
2. Why am i getting current_picoampere = 5*10^5? is this too high?
3. What gain to i pass I2D for 100kOHM, where can i find a table/formula to calculate this based on resistance ?
4. What errors are in the code that are giving me such a low res output ?

Here is the code:

``````/*
FROM https://community.nxp.com/t5/NFC/Measure-resistance-NHS3152/m-p/831045

1. Set the configuration of the analog pins to IOCON_FUNC_1
2. Connect the DAC to ANA1, set a continuous conversion of 1.25V.
3. Connect the I2D to ANA4, configure correctly and start a conversion. Only when a conversion is started, current will start flowing over your resistor. The current will continue to flow when the conversion ends. -> a
4. Connect the ADC to ANA4, and measure the voltage. -> v4
5. Connect the ADC to ANA1, and measure the voltage. -> v1

*/

/* ------------------------------------------------------------------------- */

#include <string.h>
#include <stdlib.h>
#include <stdio.h> // contains sprintf function (needs to be included to avoid : https://stackoverflow.com/questions/8440816/warning-implicit-declaration-of-function
#include "board.h"
#include "ndeft2t/ndeft2t.h"

/* ------------------------------------------------------------------------- */

#define LOCALE "en" /**< Language used when creating TEXT records. */
#define MIME "nhs31xx/example.ndef" /**< Mime type used when creating MIME records. */

/** The URL will be used in a single-record NDEF message. */
static const uint8_t sUrl[MAX_URI_PAYLOAD + 1 /* NUL */] = "nxp.com/NTAGSMARTSENSOR";

/**
* The text and the MIME data are always presented together, in a dual-record NDEF message.
* Payload length is split evenly between TEXT and MIME.
*/
NDEFT2T_TEXT_RECORD_OVERHEAD(true, sizeof(LOCALE) - 1) + \
NDEFT2T_MIME_RECORD_OVERHEAD(true, sizeof(MIME) - 1)) / 2))
static uint8_t sText[MAX_TEXT_PAYLOAD] = "10 V1-V4";

/** @copydoc MAX_TEXT_PAYLOAD */
static uint8_t sBytes[MAX_MIME_PAYLOAD] = {0, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE};

/* ------------------------------------------------------------------------- */

/**
* Used to determine which NDEF message must be generated.
* - @c true: generate a single-record NDEF message containing a URL.
* - @c false: generate a dual-record NDEF message containing a TEXT and a MIME record.
*/
static bool sState;

static volatile bool sButtonPressed = false; /** @c true when the WAKEUP button is pressed on the Demo PCB */
static volatile bool sMsgAvailable = false; /** @c true when a new NDEF message has been written by the tag reader. */
static volatile bool sFieldPresent = false; /** @c true when an NFC field is detected and the tag is selected. */

static void GenerateNdef_Url(void);
static void GenerateNdef_TextMime(void);
static void ParseNdef(void);

/* ------------------------------------------------------------------------- */

//Store adc_1, adc_4, current and resistance value
static volatile float adcInput_4 = 5.0;  // 4. store V input 4
static volatile float adcInput_1 = 5.0; //  5. store V input 1
static volatile int current_native; // 3. store I2D ana 4
static volatile int current_picoampere; // 3. store I2D ana4
static volatile double resval = -1; // store resistance calculated:  (dcInput_1-adcInput_4)/Current_picoampere*10e-6

static void adcdac_nss_example_1(void); //continuous DAC ana1
static void i2d_nss_example_1(void); //I2D ana4
static void adcdac_nss_example_3(void); //NEW single shot get ADC value ana4
static void adcdac_nss_example_3_2(void); //NEW single shot get ADC value ana1

/**
* Handler for PIO0_0 / WAKEUP pin.
* Overrides the WEAK function in the startup module.
*/
void PIO0_IRQHandler(void)
{
Chip_GPIO_ClearInts(NSS_GPIO, 0, 1);
sButtonPressed = true; /* Handled in main loop */
}

/**
* Called under interrupt.
* @see NDEFT2T_FIELD_STATUS_CB
* @see pNdeft2t_FieldStatus_Cb_t
*/
void App_FieldStatusCb(bool status)
{
if (status) {
LED_On(LED_RED);
}
else {
LED_Off(LED_RED);
}
sFieldPresent = status; /* Handled in main loop */
}

/**
* Called under interrupt.
* @see NDEFT2T_MSG_AVAILABLE_CB
* @see pNdeft2t_MsgAvailable_Cb_t
*/
void App_MsgAvailableCb(void)
{
sMsgAvailable = true; /* Handled in main loop */
}

/* ------------------------------------------------------------------------- */

/** Generates a single-record NDEF message containing a URL, and copies it to the NFC shared memory. */
static void GenerateNdef_Url(void)
{
uint8_t instance[NDEFT2T_INSTANCE_SIZE];
uint8_t buffer[NFC_SHARED_MEM_BYTE_SIZE];
NDEFT2T_CREATE_RECORD_INFO_T recordInfo = {.pString = NULL /* don't care */,
.shortRecord = true,
.uriCode = 0x01 /* "http://www." */};
NDEFT2T_CreateMessage(instance, buffer, NFC_SHARED_MEM_BYTE_SIZE, true);
if (NDEFT2T_CreateUriRecord(instance, &recordInfo)) {
if (NDEFT2T_WriteRecordPayload(instance, sUrl, (int)strlen((char *)sUrl))) {
NDEFT2T_CommitRecord(instance);
}
}
NDEFT2T_CommitMessage(instance); /* Copies the generated message to NFC shared memory. */
}

/** Generates a dual-record NDEF message containing a TEXT and a MIME record, and copies it to the NFC shared memory. */
static void GenerateNdef_TextMime(void)
{
uint8_t instance[NDEFT2T_INSTANCE_SIZE];
uint8_t buffer[NFC_SHARED_MEM_BYTE_SIZE];
NDEFT2T_CREATE_RECORD_INFO_T textRecordInfo = {.pString = (uint8_t *)"en" /* language code */,
.shortRecord = true,
.uriCode = 0 /* don't care */};
NDEFT2T_CREATE_RECORD_INFO_T mimeRecordInfo = {.pString = (uint8_t *)MIME /* mime type */,
.shortRecord = true,
.uriCode = 0 /* don't care */};
NDEFT2T_CreateMessage(instance, buffer, NFC_SHARED_MEM_BYTE_SIZE, true);
if (NDEFT2T_CreateTextRecord(instance, &textRecordInfo)) {
if (NDEFT2T_WriteRecordPayload(instance, sText, sizeof(sText) - 1 /* exclude NUL char */)) {
NDEFT2T_CommitRecord(instance);
}
}
if (NDEFT2T_CreateMimeRecord(instance, &mimeRecordInfo)) {
if (NDEFT2T_WriteRecordPayload(instance, sBytes, sizeof(sBytes))) {
NDEFT2T_CommitRecord(instance);
}
}
NDEFT2T_CommitMessage(instance); /* Copies the generated message to NFC shared memory. */
}

/** Parses the NDEF message in the NFC shared memory, and copies the TEXT and MIME payloads. */
static void ParseNdef(void)
{
uint8_t instance[NDEFT2T_INSTANCE_SIZE];
uint8_t buffer[NFC_SHARED_MEM_BYTE_SIZE];
NDEFT2T_PARSE_RECORD_INFO_T recordInfo;
int len = 0;
uint8_t *pData = NULL;

if (NDEFT2T_GetMessage(instance, buffer, NFC_SHARED_MEM_BYTE_SIZE)) {
while (NDEFT2T_GetNextRecord(instance, &recordInfo) != false) {
pData = (uint8_t *)NDEFT2T_GetRecordPayload(instance, &len);
switch (recordInfo.type) {
case NDEFT2T_RECORD_TYPE_TEXT:
if ((size_t)len <= MAX_TEXT_PAYLOAD) {
memcpy(sText, pData, (size_t)len);
memset(sText + len, 0, MAX_TEXT_PAYLOAD - (size_t)len);
}
break;
case NDEFT2T_RECORD_TYPE_MIME:
if ((size_t)len <= MAX_MIME_PAYLOAD) {
memcpy(sBytes, pData, (size_t)len);
memset(sBytes + len, 0, MAX_MIME_PAYLOAD - (size_t)len);
}
break;
default:
/* ignore */
break;
}
}
}
}

// 1. Set the configuration of the analog pins to IOCON_FUNC_1
// 2. Connect the DAC to ANA1, set a continuous conversion of 1.25V.

void adcdac_nss_example_1(void) // Modified IOCON_ANA0_0 --> IOCON_ANA0_1 & ADCDAC_IO_ANA0_0 --> ADCDAC_IO_ANA0_1
{
Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_1, IOCON_FUNC_1); // IOCON_FUN_1
}

/* ------------------------------------------------------------------------- */
// 3. Connect the I2D to ANA4, configure correctly and start a conversion. Only when a conversion is started, current will start flowing over your resistor. The current will continue to flow when the conversion ends. -> a

// FROM i2d_nss_example_1

void i2d_nss_example_1(void)
{
//! [i2d_nss_example_1]
int i2dValue;
int i2dNativeValue;
Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_4, IOCON_FUNC_1); // IOCON_FUN_1
Chip_I2D_Init(NSS_I2D);
Chip_I2D_Setup(NSS_I2D, I2D_SINGLE_SHOT, I2D_SCALER_GAIN_10_1, I2D_CONVERTER_GAIN_HIGH, 100);
Chip_I2D_SetMuxInput(NSS_I2D, I2D_INPUT_ANA0_4);
Chip_I2D_Start(NSS_I2D);
while (!(Chip_I2D_ReadStatus(NSS_I2D) & I2D_STATUS_CONVERSION_DONE)) {
; /* wait */
}
i2dNativeValue = Chip_I2D_GetValue(NSS_I2D);
i2dValue = Chip_I2D_NativeToPicoAmpere(i2dNativeValue, I2D_SCALER_GAIN_10_1, I2D_CONVERTER_GAIN_HIGH, 100);
Chip_I2D_DeInit(NSS_I2D);
//! [i2d_nss_example_1]

current_native = i2dNativeValue;
current_picoampere = i2dValue;
}

// 4. Connect the ADC to ANA4, and measure the voltage. -> v4

//FROM Example 3 - Single-shot Analog-to-Digital Conversion without IRQ

// The conversion: adc_input_voltage = (native_value * 1.2V) / 2825 + 0.09V
void adcdac_nss_example_3(void) // Modifications:  IOCON_ANA0_5--> IOCON_ANA0_4 & converted adcinput_4= (adcInput_4 * 1.2) / 2825 + 0.09
{
Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_4, IOCON_FUNC_1);

; /* Wait until measurement completes. For single-shot mode only! */
}

adcInput_4= (adcInput_4 * 1.2) / 2825 + 0.09; // CONVERSION added line

}

void adcdac_nss_example_3_2(void) // Modifications:  IOCON_ANA0_5--> IOCON_ANA0_1 & converted adcinput_1= (adcInput_1 * 1.2) / 2825 + 0.09
{
Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_1, IOCON_FUNC_1);

; /* Wait until measurement completes. For single-shot mode only! */
}

adcInput_1= (adcInput_1 * 1.2) / 2825 + 0.09; // CONVERSION added line

}

// MAIN
int main(void)
{
Board_Init();
NDEFT2T_Init();
NVIC_EnableIRQ(PIO0_IRQn); /* PIO0_IRQHandler is called when this interrupt fires. */
Chip_GPIO_EnableInt(NSS_GPIO, 0, 1);

// 	for ever,  WHILE field is detected: 2. Connect the DAC to ANA1, set a continuous conversion of 1.25V.
for (;;) {
while (sFieldPresent) {

// 2. Connect the DAC to ANA1  -output Voltage
// 3. Connect the I2D to ANA4, - read current ana4 through resistor
i2d_nss_example_1();
// 4. Connect the ADC to ANA4, and measure the voltage. ->v4
// 5. Connect the ADC to ANA1, and measure the voltage. -> v1
// generate the message only once per field???
GenerateNdef_TextMime();
resval = (adcInput_1-adcInput_4)/(current_picoampere * 10e-5); // (v1-v4)/(I4pico * 10^-6) V/I=R [V/A =ohm]
sprintf((char *)sText, "adc_1: %4.2f adc_4: %4.2f pA: %4.d res: %4.4f, nat: %4.d", adcInput_1, adcInput_4,current_picoampere, resval,current_native );//commented in from Thesis, changes payloadText to sText

// attach message to be read
if (sMsgAvailable) {
sMsgAvailable = false;
ParseNdef();
}
}

Chip_PMU_PowerMode_EnterDeepSleep();
}
return 0;

}

``````

Thanks,

Leo

P.S. since the update to the community page with the subsequent series of emails for badges, all your emails have gone to spam - maybe this is happening to other clients of yours.

4 Replies
148 Views
Contributor III

Hi, is there no solution to this problem, or is it out of the scope of this community?

220 Views
Contributor III

Hi Dries,

Thanks for your help,

I updated Chip_I2D_Setup as suggested:

`225 Chip_I2D_Setup(NSS_I2D, I2D_SINGLE_SHOT, I2D_SCALER_GAIN_10_1, I2D_CONVERTER_GAIN_LOW, 100);`

and converted pico (this was emabrassing)

`306 resval = (adcInput_1 - adcInput_4) / (current_picoampere * 1e-12)`

i also changed output code:

`307 sprintf((char *)sText, "adc_1: %6.2f adc_4: %6.2f current_picoampere: %8.d resistance: %e current_native: %6.d", adcInput_1, adcInput_4,current_picoampere, resval,current_native );`

I get the following output:

2. adc_1:1.34 adc_4:0.56 current_picoampere:179140 resistance:4.303748e+06 current_native: 8957
3. adc_1:1.34 adc_4:0.58 current_picoampere: 179220 resistance:4.249684e+06 current_native:8961

Possible things that could be affecting results:

I am running Debug--> resume connect via LPC-link 2. maybe running the code this way affects outcome?

I haven't connected anything to the GND pin of NHS3152 - only connection is ana1-resistor[100kOhm]-ana4

Possible conversion errors for V1, V4, I2D

Thanks,

leo

FULL NEW CODE:

`/*FROM https://community.nxp.com/t5/NFC/Measure-resistance-NHS3152/m-p/8310451. Set the configuration of the analog pins to IOCON_FUNC_12. Connect the DAC to ANA1, set a continuous conversion of 1.25V.3. Connect the I2D to ANA4, configure correctly and start a conversion. Only when a conversion is started, current will start flowing over your resistor. The current will continue to flow when the conversion ends. -> a4. Connect the ADC to ANA4, and measure the voltage. -> v45. Connect the ADC to ANA1, and measure the voltage. -> v1*//* ------------------------------------------------------------------------- */#include <string.h>#include <stdlib.h>#include <stdio.h> // contains sprintf function (needs to be included to avoid : https://stackoverflow.com/questions/8440816/warning-implicit-declaration-of-function#include "board.h"#include "ndeft2t/ndeft2t.h"/* ------------------------------------------------------------------------- */#define LOCALE "en" /**< Language used when creating TEXT records. */#define MIME "nhs31xx/example.ndef" /**< Mime type used when creating MIME records. *//** The URL will be used in a single-record NDEF message. */#define MAX_URI_PAYLOAD (254 - NDEFT2T_MSG_OVERHEAD(true, NDEFT2T_URI_RECORD_OVERHEAD(true)))static const uint8_t sUrl[MAX_URI_PAYLOAD + 1 /* NUL */] = "nxp.com/NTAGSMARTSENSOR";/*** The text and the MIME data are always presented together, in a dual-record NDEF message.* Payload length is split evenly between TEXT and MIME.*/#define MAX_TEXT_PAYLOAD (254 - (NDEFT2T_MSG_OVERHEAD(true, \NDEFT2T_TEXT_RECORD_OVERHEAD(true, sizeof(LOCALE) - 1) + \NDEFT2T_MIME_RECORD_OVERHEAD(true, sizeof(MIME) - 1)) / 2))static uint8_t sText[MAX_TEXT_PAYLOAD] = "10 V1-V4";/** @copydoc MAX_TEXT_PAYLOAD */#define MAX_MIME_PAYLOAD MAX_TEXT_PAYLOADstatic uint8_t sBytes[MAX_MIME_PAYLOAD] = {0, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE};/* ------------------------------------------------------------------------- *//*** Used to determine which NDEF message must be generated.* - @c true: generate a single-record NDEF message containing a URL.* - @c false: generate a dual-record NDEF message containing a TEXT and a MIME record.*/static bool sState;static volatile bool sButtonPressed = false; /** @c true when the WAKEUP button is pressed on the Demo PCB */static volatile bool sMsgAvailable = false; /** @c true when a new NDEF message has been written by the tag reader. */static volatile bool sFieldPresent = false; /** @c true when an NFC field is detected and the tag is selected. */static void GenerateNdef_Url(void);static void GenerateNdef_TextMime(void);static void ParseNdef(void);/* ------------------------------------------------------------------------- *///Store adc_1, adc_4, current and resistance valuestatic volatile float adcInput_4 = 5.0; // 4. store V input 4static volatile float adcInput_1 = 5.0; // 5. store V input 1static volatile int current_native; // 3. store I2D ana 4static volatile int current_picoampere; // 3. store I2D ana4static volatile double resval = -1; // store resistance calculated: (dcInput_1-adcInput_4)/Current_picoampere*10e-6static void adcdac_nss_example_1(void); //continuous DAC ana1static void i2d_nss_example_1(void); //I2D ana4static void adcdac_nss_example_3(void); //NEW single shot get ADC value ana4static void adcdac_nss_example_3_2(void); //NEW single shot get ADC value ana1/*** Handler for PIO0_0 / WAKEUP pin.* Overrides the WEAK function in the startup module.*/void PIO0_IRQHandler(void){Chip_GPIO_ClearInts(NSS_GPIO, 0, 1);sButtonPressed = true; /* Handled in main loop */}/*** Called under interrupt.* @see NDEFT2T_FIELD_STATUS_CB* @see pNdeft2t_FieldStatus_Cb_t*/void App_FieldStatusCb(bool status){if (status) {LED_On(LED_RED);}else {LED_Off(LED_RED);}sFieldPresent = status; /* Handled in main loop */}/*** Called under interrupt.* @see NDEFT2T_MSG_AVAILABLE_CB* @see pNdeft2t_MsgAvailable_Cb_t*/void App_MsgAvailableCb(void){sMsgAvailable = true; /* Handled in main loop */}/* ------------------------------------------------------------------------- *//** Generates a single-record NDEF message containing a URL, and copies it to the NFC shared memory. */static void GenerateNdef_Url(void){uint8_t instance[NDEFT2T_INSTANCE_SIZE];uint8_t buffer[NFC_SHARED_MEM_BYTE_SIZE];NDEFT2T_CREATE_RECORD_INFO_T recordInfo = {.pString = NULL /* don't care */,.shortRecord = true,.uriCode = 0x01 /* "http://www." */};NDEFT2T_CreateMessage(instance, buffer, NFC_SHARED_MEM_BYTE_SIZE, true);if (NDEFT2T_CreateUriRecord(instance, &recordInfo)) {if (NDEFT2T_WriteRecordPayload(instance, sUrl, (int)strlen((char *)sUrl))) {NDEFT2T_CommitRecord(instance);}}NDEFT2T_CommitMessage(instance); /* Copies the generated message to NFC shared memory. */}/** Generates a dual-record NDEF message containing a TEXT and a MIME record, and copies it to the NFC shared memory. */static void GenerateNdef_TextMime(void){uint8_t instance[NDEFT2T_INSTANCE_SIZE];uint8_t buffer[NFC_SHARED_MEM_BYTE_SIZE];NDEFT2T_CREATE_RECORD_INFO_T textRecordInfo = {.pString = (uint8_t *)"en" /* language code */,.shortRecord = true,.uriCode = 0 /* don't care */};NDEFT2T_CREATE_RECORD_INFO_T mimeRecordInfo = {.pString = (uint8_t *)MIME /* mime type */,.shortRecord = true,.uriCode = 0 /* don't care */};NDEFT2T_CreateMessage(instance, buffer, NFC_SHARED_MEM_BYTE_SIZE, true);if (NDEFT2T_CreateTextRecord(instance, &textRecordInfo)) {if (NDEFT2T_WriteRecordPayload(instance, sText, sizeof(sText) - 1 /* exclude NUL char */)) {NDEFT2T_CommitRecord(instance);}}if (NDEFT2T_CreateMimeRecord(instance, &mimeRecordInfo)) {if (NDEFT2T_WriteRecordPayload(instance, sBytes, sizeof(sBytes))) {NDEFT2T_CommitRecord(instance);}}NDEFT2T_CommitMessage(instance); /* Copies the generated message to NFC shared memory. */}/** Parses the NDEF message in the NFC shared memory, and copies the TEXT and MIME payloads. */static void ParseNdef(void){uint8_t instance[NDEFT2T_INSTANCE_SIZE];uint8_t buffer[NFC_SHARED_MEM_BYTE_SIZE];NDEFT2T_PARSE_RECORD_INFO_T recordInfo;int len = 0;uint8_t *pData = NULL;if (NDEFT2T_GetMessage(instance, buffer, NFC_SHARED_MEM_BYTE_SIZE)) {while (NDEFT2T_GetNextRecord(instance, &recordInfo) != false) {pData = (uint8_t *)NDEFT2T_GetRecordPayload(instance, &len);switch (recordInfo.type) {case NDEFT2T_RECORD_TYPE_TEXT:if ((size_t)len <= MAX_TEXT_PAYLOAD) {memcpy(sText, pData, (size_t)len);memset(sText + len, 0, MAX_TEXT_PAYLOAD - (size_t)len);}break;case NDEFT2T_RECORD_TYPE_MIME:if ((size_t)len <= MAX_MIME_PAYLOAD) {memcpy(sBytes, pData, (size_t)len);memset(sBytes + len, 0, MAX_MIME_PAYLOAD - (size_t)len);}break;default:/* ignore */break;}}}}// 1. Set the configuration of the analog pins to IOCON_FUNC_1// 2. Connect the DAC to ANA1, set a continuous conversion of 1.25V.void adcdac_nss_example_1(void) // Modified IOCON_ANA0_0 --> IOCON_ANA0_1 & ADCDAC_IO_ANA0_0 --> ADCDAC_IO_ANA0_1{//! [adcdac_nss_example_1]Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_1, IOCON_FUNC_1); // IOCON_FUN_1Chip_ADCDAC_Init(NSS_ADCDAC0);Chip_ADCDAC_SetMuxDAC(NSS_ADCDAC0, ADCDAC_IO_ANA0_1);Chip_ADCDAC_SetModeDAC(NSS_ADCDAC0, ADCDAC_CONTINUOUS);Chip_ADCDAC_WriteOutputDAC(NSS_ADCDAC0, 3000);//! [adcdac_nss_example_1]}/* ------------------------------------------------------------------------- */// 3. Connect the I2D to ANA4, configure correctly and start a conversion. Only when a conversion is started, current will start flowing over your resistor. The current will continue to flow when the conversion ends. -> a// FROM i2d_nss_example_1void i2d_nss_example_1(void){//! [i2d_nss_example_1]int i2dValue;int i2dNativeValue;Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_4, IOCON_FUNC_1); // IOCON_FUN_1Chip_I2D_Init(NSS_I2D);Chip_I2D_Setup(NSS_I2D, I2D_SINGLE_SHOT, I2D_SCALER_GAIN_10_1, I2D_CONVERTER_GAIN_LOW, 100);Chip_I2D_SetMuxInput(NSS_I2D, I2D_INPUT_ANA0_4);Chip_I2D_Start(NSS_I2D);while (!(Chip_I2D_ReadStatus(NSS_I2D) & I2D_STATUS_CONVERSION_DONE)) {; /* wait */}i2dNativeValue = Chip_I2D_GetValue(NSS_I2D);i2dValue = Chip_I2D_NativeToPicoAmpere(i2dNativeValue, I2D_SCALER_GAIN_10_1, I2D_CONVERTER_GAIN_HIGH, 100);Chip_I2D_DeInit(NSS_I2D);//! [i2d_nss_example_1]current_native = i2dNativeValue;current_picoampere = i2dValue;}// 4. Connect the ADC to ANA4, and measure the voltage. -> v4//FROM Example 3 - Single-shot Analog-to-Digital Conversion without IRQ// The conversion: adc_input_voltage = (native_value * 1.2V) / 2825 + 0.09Vvoid adcdac_nss_example_3(void) // Modifications: IOCON_ANA0_5--> IOCON_ANA0_4 & converted adcinput_4= (adcInput_4 * 1.2) / 2825 + 0.09{//! [adcdac_nss_example_3]Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_4, IOCON_FUNC_1);//Chip_ADCDAC_Init(NSS_ADCDAC0);Chip_ADCDAC_SetMuxADC(NSS_ADCDAC0, ADCDAC_IO_ANA0_4);Chip_ADCDAC_SetInputRangeADC(NSS_ADCDAC0, ADCDAC_INPUTRANGE_WIDE);Chip_ADCDAC_SetModeADC(NSS_ADCDAC0, ADCDAC_SINGLE_SHOT);Chip_ADCDAC_StartADC(NSS_ADCDAC0);while (!(Chip_ADCDAC_ReadStatus(NSS_ADCDAC0) & ADCDAC_STATUS_ADC_DONE)) {; /* Wait until measurement completes. For single-shot mode only! */}adcInput_4 = Chip_ADCDAC_GetValueADC(NSS_ADCDAC0);adcInput_4= (adcInput_4 * 1.2) / 2825 + 0.09; // CONVERSION added line//! [adcdac_nss_example_3]}void adcdac_nss_example_3_2(void) // Modifications: IOCON_ANA0_5--> IOCON_ANA0_1 & converted adcinput_1= (adcInput_1 * 1.2) / 2825 + 0.09{//! [adcdac_nss_example_3]Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_1, IOCON_FUNC_1);//Chip_ADCDAC_Init(NSS_ADCDAC0);Chip_ADCDAC_SetMuxADC(NSS_ADCDAC0, ADCDAC_IO_ANA0_1);Chip_ADCDAC_SetInputRangeADC(NSS_ADCDAC0, ADCDAC_INPUTRANGE_WIDE);Chip_ADCDAC_SetModeADC(NSS_ADCDAC0, ADCDAC_SINGLE_SHOT);Chip_ADCDAC_StartADC(NSS_ADCDAC0);while (!(Chip_ADCDAC_ReadStatus(NSS_ADCDAC0) & ADCDAC_STATUS_ADC_DONE)) {; /* Wait until measurement completes. For single-shot mode only! */}adcInput_1 = Chip_ADCDAC_GetValueADC(NSS_ADCDAC0);adcInput_1= (adcInput_1 * 1.2) / 2825 + 0.09; // CONVERSION added line//! [adcdac_nss_example_3]}// MAINint main(void){Board_Init();NDEFT2T_Init();NVIC_EnableIRQ(PIO0_IRQn); /* PIO0_IRQHandler is called when this interrupt fires. */Chip_GPIO_EnableInt(NSS_GPIO, 0, 1);// for ever, WHILE field is detected: 2. Connect the DAC to ANA1, set a continuous conversion of 1.25V.for (;;) {while (sFieldPresent) {// 2. Connect the DAC to ANA1 -output Voltageadcdac_nss_example_1();// 3. Connect the I2D to ANA4, - read current ana4 through resistori2d_nss_example_1();// 4. Connect the ADC to ANA4, and measure the voltage. ->v4adcdac_nss_example_3();// 5. Connect the ADC to ANA1, and measure the voltage. -> v1adcdac_nss_example_3_2();// generate the message only once per field???GenerateNdef_TextMime();resval = (adcInput_1-adcInput_4)/(current_picoampere * 1e-12); // (v1-v4)/(I4pico * 1e-12) V/I=R [V/A =ohm]sprintf((char *)sText, "adc_1: %6.2f adc_4: %6.2f current_picoampere: %8.d resistance: %e current_native: %6.d", adcInput_1, adcInput_4,current_picoampere, resval,current_native );//commented in from Thesis, changes payloadText to sText// attach message to be readif (sMsgAvailable) {sMsgAvailable = false;ParseNdef();}}Chip_PMU_PowerMode_EnterDeepSleep();}return 0;}`

222 Views
NXP Employee

Hello Leo,

Can you adjust the parameters in Chip_I2D_Setup? Given your expected current at 100kOhm, you'll need to use the 25uA range, which corresponds to these parameters:

`Chip_I2D_Setup(NSS_I2D, I2D_SINGLE_SHOT, I2D_SCALER_GAIN_10_1, I2D_CONVERTER_GAIN_LOW, 100);`

See also Chapter 8 Current-to-Digital converter (I2D) > Specifications in the datasheet.

The conversion from van pico Ampère to Ohm is then calculated as: resval = (adcInput_1 - adcInput_4) / (current_picoampere * 1e-12)

Let me know your results!

Best,
Dries.

194 Views
Contributor III

Hi @driesmoors

is there any update on why i am getting erroneous values for Resistance?

I have tested for different resistances (1MOhm, 2Mohm, 3Mohm) and resistance measured is scaling correclty with resitance_real, but still not the correct value.

Best,

Leo