TDC1000-C2000EVM: Measuring distance at 125KHz

Hi Esteban,

Thank you for posting to the sensors forum. 

Today is a holiday in the US and our team is out of office. We will do our best to provide a response by end of day July 5. 

Best regards,

Jesse

Hi Jesse, 

Thank you for your reply, I look forward to your comments.

Best regards, 

Hello Esteban,

Thanks for your patience while we were out of office. Have you configured your listening window appropriately? 

The RX path of the TDC1000 is only active during a configured time after a measurement is started, depending on the configuration the device could be triggering a STOP pulse based on the excitation pulses hence why you would see the device generate a STOP even though nothing is connected.

Also if you could try changing your filter stage similar to what is seen on the TDC1000-GASEVM, this filter is configured for 58kHz to 300kHz. Typically for water based applications 1MHz transducers are used.

Do you mind sharing more about what your application is for the TDC1000?

Best,

Isaac

Hello Isaac,

Thanks for your reply. I've successfully managed to apply the correct filter and observe the TOF variation at short distances (3 to 7cm) using SHORT_TOF. However, it only works with an ECHO_QUAL_THLD lower than |125mV|, despite having the PGA_GAIN set to 21dB.

When attempting to measure distances longer than 15cm, I'm  not able to achieve success with either SHORT_TOF or without it.

1) Should I remove C4 and C5 to use Resistive LNA Feedback? I've already added 890 ohms before the RX1 input.

2) How can I use HV Driver?

Best regards,

Hello Esteban,

Typically resistive feedback is better for the frequency range that you are looking at. If you are operating 500kHz and up then capacitive feedback is used.

You can use a circuit similar to what is found in the BSTEVM. Unfortunately, we no longer sell this board anymore but the circuit can be found here in case you would like to recreate it: https://www.ti.com/lit/ug/sniu026a/sniu026a.pdf

Have you looked into our TUSS44x0 devices? They offer higher voltage options and better dynamic range compared to the TDC1000. 

Best,

Isaac

Hello,

Ok I'm using resistive feedback but it's still the same. On the TDC1000_C2000_EVM software I can enable "HV Driver EN1", how does it work? 
The generated TX signal is about 700mVpp, can I increase that voltage? 

If I can measure TOF with TDC1000, I'll bought the TUSS44x0 but first I need to validate the technology.

Thanks, 

Hello Esteban,

HV Driver EN1 will not work unless if you have a separate board that has the high voltage driver for the transducers. Unfortunately, we discontinued this board and no longer sell it. Thats why I linked the documentation to the boost EVM above.

The TX voltage does sound rather low, you should see about 5V on the TX output. I haven't tried to check what happens if the HV is checked without the HV driver connected. Can you try disabling the HV Driver EN1 checkbox and verify you are seeing the 5V TX output?

Also on another note we typically don't recommend the TDC1000 for air based applications and its mostly recommended for water based applications because this device does not have a very large dynamic range compared to our newer devices so this could be why you are having problems on your end and the device can also be finicky when configuring the external filter options. Our newer devices like the TUSS44x0 series of devices and PGA460 are much easier to configure and the offer a larger dynamic range when compared than our older generation.

Best,

Isaac

Ok, thanks for your reply Isaac. I need to measure the TOF (Time of Flight) between two hydrophones with a resonant frequency of 149.5 kHz, submerged in fresh water. First, I want to measure distance, and after that, I need to measure flow with the transducers separated by 2 meters. Which EVM do you recommend?

Meanwhile, I want to continue testing with the TDC1000. If I have the HV Driver EN disabled, why can't I see 5V on the TX output with the transducer connected or even disconnected? Should I remove R3/R4 on the TX path?

Hello Esteban,

Thanks for the background on this. If you are working with water I believe your transducer frequency is rather low from what we typically see on these types of applications. Typically we see 1MHz transducer frequency but the distances are much smaller than what you are looking at, so perhaps for 2M 150kHz may be good to help you get to the distance you need without having to use a very large voltage since at ~30V with 1MHz we were able to reliably measure about 1m.

Try setting up the board to the capacitive coupling again and check if you can see 5V on the TX, but I think you will need to bump your voltage higher than the 5V to reach your 2m target.

In general we no longer really recommend the TDC1000 for flow measurements due to a bug on the comparator that causes some loss in measurement accuracy, we typically recommend MSP430FR6043 series for flow measurements. In this scenario you will still have challenges due to the low voltage on the driving circuitry of that device as well. We have had a few customers implement flow with the TUSS4470 devices when they must handle a larger range but this solution tends to be more expensive as it does require two separate devices since this device is not a two channel solution like the TDC1000 but its easier to reach the larger voltages with this line of devices since you don't need all the added circuitry that the TDC1000 or MSP430FR6043 may need.

Best,

Isaac