LDC2114EVM: LDC2114 sensor reading

Ashrith,

Thank you for your inquiry and your interest in TI products.
I have a few questions:
1. What is the target frequency for your "G" coil and 470pF LC combination?
2. Can you probe the coil & PCB with an oscilloscope and a decent probe to verify the signal is close to the target frequency and has the recommended amplitude?
3. What DC voltages are you measuring on the coil?

Please feel free to consult our Inductive Sensing FAQ page or more information. 

Regards,
John

1.  The target frequency is 2.7MHz. 

On probing the coil we didn't see any signal on the oscilloscope and the voltage across the cap is 0. 

How to verify that the device is functioning and active? I only configure the registers and wait for registers refreshed message at the bottom left. 

thanks 

Ashrith,

There may be an open connection between the device PCB and the coil. Could you check the connection with an ohm-meter?
If that looks okay, would you please measure the DC voltage from either end of the coil to ground?
Please also confirm the EN (addr 0x0C) register settings coincide with the channel that has the coil attached.

Regards,
John

John,

The connection exists . DC voltage is 0.87v and I have enabled channel 0 with my coil connected to the same on EVM. I have also attached a picture of the connection above. 

Ashrith,

Have you tried holding a conductive target at varying distances above the coil? Please give that a try and see if it affects the output data.

If you have, and it hasn't changed anything, then perhaps the RP of the coil is too small and there isn't enough drive current for the coil.
Some rough calculations for RP based on the graphs for the 'G' coil give me about 3k.
From the image you uploaded, the SENSE0_CONFIG register, BIT7 is the default value of '0', which corresponds to an RP of 350-4k ohms, which should be okay.
As an experiment, please try flipping bit 7 of SENSE0_CONFIG register from '0' to '1'.
This will shift the range of supported RP0 from 350-4k to 800-10k.

Please let me know how it goes.

Regards,
John

Hi John,

I did change the configs but there seems to be making no difference. We initially saw there was signal loss due to the wire connectors and hence directly soldered the coil pcb onto the evm using male pinouts. Kindly provide any suggestions possible. 

Thank you

Ashrith,

I don't have any other suggestions at this point. I will try to reproduce your findings in the lab and update this thread by the end of the week.

Regards,
John

Thanks you John. I will wait for your update!

Ashrith,

Did you place the 470pF cap on the coil board, or did you replace the 47pF cap on the device EVM?
Regards,
John

John,
We placed the cap on the coil board

Thanks

Did you remove the 47pF cap (C6, I believe) on the device EVM?

Regards,
John

No, I have not removed any cap/component from the evm

Thanks Ashrith.
I will try to reproduce your findings in the lab and will update this thread by Friday.

Regards,
John

Ashrith,

I reproduced your set-up and got credible data from the GUI with default device settings.
There was an initial problem because a wire strand was intermittently shorting the coil input pads.
Once that was corrected, it ran fine and produced credible data. 

Just so you know, the LDC2114 is intended for button applications, not linear/ sensors like the coil you are using.
I don't think this is the problem you are seeing; you may have a board failure.
If your application is indeed a linear sensor, you might consider using the  LDC1612 or the LDC3114 in Raw Data mode.

Regards,
John

John,

Thank you very much for getting back to me. We intended to use the ldc2114 for linear sensing applications. Based on your feedback we will consider the ldc1612. 

could you please share the data graph that you were able to reproduce with the same setup? 
Also, is there any way to verify the LDC2114 evm board  is functioning right? If not , then can I ask for a replacement? 

Regards, 
Ashrith

Ashrith,

The plot I got appears below.
I don't know the policy replacing our eval boards. You would have to check with our customer support team for that.

Regards,
John