lpc55s28 adc0_12 not working

[PatrickLai]

Hi,

I'm configuring ADC0_3 and ADC0_12 for LPC55S28. ADC0_3 can get different values for different input voltages, but ADC0_12 always gets 4092~4095 for any input voltages. Please help to check what is the possible cause of this issue. Attached my current changes for ADC

Best regards,

Patrick

[Alice_Yang]

Hello @PatrickLai 

Please check your hardware to verify whether ADC0_12 is connected to a high voltage on the board. Also, please confirm that you are connected to the correct pin.

Thank you.

BR

Alice

[PatrickLai]

Hi Alice,
I've tested the input voltage of ADC0_12 pin on the MCU is 1.9V, so the hardware should be ok. but the adc value is still in range of 4091 and 4095

[Alice_Yang]

Hello @PatrickLai 

Please connect GND for testing.

If the issue persists, use the configuration tool to set up the ADC and this channel.

BR

Alice

[PatrickLai]

Hi Alice,

I connected to ground and the adc value is still not right. I have trouble using config tool to setup adc. So I used the sample code lpadc_polling from the SDK. I only change the ADC channel to ADC0_12 and it still doesn't work. The ADC0_3 is ok. Could you please help to check based on the sample code and my configuration?

[Alice_Yang]

Hello @PatrickLai 

Do you use the LPCXpresso55S28-EVK board? If yes, please check the schematic; this pin is connected to VDD.

BR

Alice

[PatrickLai]

Hi Alice,

I tested on the evk, and tried removing the R75 and press the USER button(SW3), adc value is still the same, around 4094~4095. Please help to check again.

Best regards,

Patrick

[Alice_Yang]

Hello @PatrickLai 

Please share your complete project.

BR

Alice

[PatrickLai]

Hi Alice,

project code uploaded.

Best regards,

Patrick

[PatrickLai]

Hi @Alice_Yang ,
Any udpate?
Best regards,
Patrick

[Alice_Yang · Accepted solution]

Hello @PatrickLai 

I'm sorry for the late reply. I’m not sure why our internal system didn’t send me a notification when you updated this thread.

Anyway, I have tested your project and checked the issue. The problem is that ADC0_12 corresponds to channel (ADCH) 4, not 12. So please change
#define DEMO_LPADC_USER_CHANNEL 12U
to
#define DEMO_LPADC_USER_CHANNEL 4U.

Also, please configure the sample channel mode to "Single-ended mode, as only the B-side channel is converted" . As shown below.

After these changes, it works correctly.

Hope it helps. 

Thank you.

BR

Alice

[PatrickLai]

Hi Alice,

It works now. Thank you for your help.

Best regards,

Patrick