I am using the PSoC5 development kit, CY8CKIT-050, and face 2 issues.

1) I received the attached error "Component SAR could not be place because no more SAR blocks are available". However, I only use 1 ADC-SAR block in PSoC Creator 2, hence I don't understand why I cannot place the ADC_SAR block. Can anyone please advise?

2)  Then I changed to use ADC_DelSig, but I found that the actual input voltage value is different from the measured output value. Eg. the input voltage is 1.893V, but the measured output value is 1.932V. There is an offset of about 0.03V. I am using a resolution of 16 for the ADC_DelSig. Can anyone advise how to reduce the offest? I have attached the program in this post.

Thanks & Regards

Well, you didn't attach the program or project, but just a picture of your Creator IDE.

Will you be so kind to upload the complete project here?

Bob

It might be that you exhausted some chip resources. For example, I see a large analog mux in your schematic. This might block the port needed for bypassing the SAR-ADC reference (you see the message about its auto placement in the log). So check which pins are used by your input pins, and look at the warnings in the log file about which resources they block.

Hi Bob,

Sorry, please find attached the project file.

Thanks & Regards

Attached is the measured value comparison between the ADC output and the actual input measured by a DMM.

Highlighted in yellow is the actual voltage input into the ADC, while the blue column is the measurement value by the ADC.

I used a DelSig_ADC for this comparison. I am not sure how to improve the accuracy.

Regards

Sorry, please refer to attached zip file.

Have a look at the datasheet for the ADC (Page 5)  concerning the different conversion modes when using a multiplexeor as it is the case in your project. It states tht you ought to use the "Multi-sample" mode to get clean and clear results and

If you do not switch between measures you should drop the first three results before the first is correctly converted. Thid behaveour is needed for some filtering which is done internally.

As I was told, interrupt latency will spoil the precision of AD-conversion and as I can see some (4?) sources for interrupts in your project I would suggest (at least in the pase of testing) to disable those ISRs during a precise measure and re-enable them after the result is there. There are some appnotes about the precision of AD-conversions and the even suggest to stop most switching within the chip (Timers, PWMs etc.) to reduce generated noise because 16 bit precision is really a lot!

Bob 

Oh yes, another one: for 16 bit ADC you'll need to call ADC_1_GetResult32() see datasheet Pg 25 on Getresult16().

Bob

Hi Hli,

Problem with the ADC_SAR is solved. This is because I have already used P0[2] and P0[4] for other purposes, which is required when the ADC_SAR is configured as 'internal Vref, bypassed'.

Thanks for your advise.