topic Re: LPC54608 Temperature Sensor in LPC Microcontrollers

LPC54608 Temperature Sensor

eileen_radzwion — Mon, 16 Dec 2019 15:07:27 GMT

ello,

I am trying to use the on-chip temperature sensor that is internally routed to the adc's channel 0. I found in the data sheet for the lpc54608 we must configure the ADC in single channel burst mode. I have used the adc driver example from the sdk version 2.6, called lpc_adc_burst.

the result after more than 9 conversions is 919. To determine what this equals in mV, i use the equation (Vref_p - Vref_n)/4095 * V_in *1000 = 2.5/4095 * 919*1000.

(with a Vrev_p = 2.5, and Vref_n = 0, and 12 bit resolution)

therefore, the input is 561mV.

Using the graph and tables from the data sheet, this can be fed into an equation based on LLS of:

mV = (-2.04)*temperature + 584 => temperature = (mV - 584)/(-2.04).

this means, in our case with 561mV we have:

temp = (561-584)/(-2.04) = 11.275°C

Considering this is sitting in ambient office temperature, I hardly think this is accurate.

again, please note, this is using the sdk 2.6 version of lpc_adc_burst with only modification to remove the getchar() to initiate the conversions

in main:

...
ADC_Configuration();

/* Enable the interrupt. */
ADC_EnableInterrupts(DEMO_ADC_BASE, kADC_ConvSeqAInterruptEnable);
NVIC_EnableIRQ(DEMO_ADC_IRQ_ID);

PRINTF("Configuration Done.\r\n");

#if defined(FSL_FEATURE_ADC_HAS_CTRL_RESOL) & FSL_FEATURE_ADC_HAS_CTRL_RESOL
PRINTF("ADC Full Range: %d\r\n", g_Adc_12bitFullRange);
#endif /* FSL_FEATURE_ADC_HAS_CTRL_RESOL */
while (1)
{
//GETCHAR();

gAdcConvSeqAIntFlag = false;

/* ADC_DoSoftwareTriggerConvSeqA(DEMO_ADC_BASE); */
/* Enable the burst mode and start the conversion. */
ADC_EnableConvSeqABurstMode(DEMO_ADC_BASE, true);

while (!gAdcConvSeqAIntFlag)
{
}
PRINTF("gAdcResultInfoStruct.result = %d\r\n", gAdcResultInfoStruct.result);
PRINTF("gAdcResultInfoStruct.channelNumber = %d\r\n", gAdcResultInfoStruct.channelNumber);
/* PRINTF("gAdcResultInfoStruct.overrunFlag = %d\r\n", gAdcResultInfoStruct.overrunFlag ? 1U : 0U); */
PRINTF("\r\n");
}
}

Re: LPC54608 Temperature Sensor

xiangjun_rong — Tue, 17 Dec 2019 05:17:33 GMT

Hi, Eileen,

I think your code is correct, your computation is correct. Note that you have to wait for 10us after power-up, then use ADC to sample the temperature sensor.

The temperature accuracy is 3.7 degree from -40 to 105 based on data sheet.

Hope it can help you

XiangJun Rong

Re: LPC54608 Temperature Sensor

eileen_radzwion — Thu, 09 Jan 2020 11:53:39 GMT

Hi,

I have rerun the test with slightly different results, I also compared to the newer version of the sdk (2.7) as i'd prefer to use the updated code, but the results there were completely unacceptable. I again have commented out the getchar as this is on a custom board, and these are the results of my testing. in 2.7 version, i had to change the code to use channel 0 rather than channel 4 in the examples.

i have included all code in the zip here, along with more details of the testing. I would prefer to use 2.7 as that is more up to date, but why is it not consistent? Also, why are the results different for 2.6 burst? this is the same board and same code?

thanks,

eileen

sdk 2.6 basic			sdk 2.6 burst			sdk 2.6 int

avg	535.2564	23.89392	avg	541.8559	20.65886	avg	537.4359	22.82554
min	534.188	23.22057	min	540.9035	20.22792	min	536.63	22.02351
max	536.63	24.41763	max	542.735	21.12572	max	539.072	23.22057

2.7 basic			2.7 burst			2.7 int

avg	468.2112	56.7592	avg	489.5849	46.28193	avg	472.619	54.59851
min	435.8974	32.79705	min	460.928	31.30073	min	438.9499	33.09632
max	517.094	72.5993	max	520.1465	60.32943	max	516.4835	71.10297

Re: LPC54608 Temperature Sensor

eileen_radzwion — Thu, 09 Jan 2020 12:46:48 GMT

sorry, but i really need some direction. i have started using the 2.6 adc burst code just so i can move on, and now, again, i'm getting result in the 915-920 range, translating to 10.95-12.45°. This is using the exact same output file from IAR that is included in the zip folder above. how can i be getting such drastically different results with the exact same image, exact same location, board, etc, etc... ?

just so you are aware, ambient temperature is 21°C

Thank you,

Eileen

Re: LPC54608 Temperature Sensor

eileen_radzwion — Wed, 05 Feb 2020 17:31:59 GMT

can i get some guidance please