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TDC1000-C2000EVM: Cannot get CT10U-30S400-1 40K transducer to work

Sam Sulaimanov
Prodigy 10 points
Part Number: TDC1000-C2000EVM
Other Parts Discussed in Thread: TDC1000, PGA460

Hi!

I have a the TDC1000-C2000EVM and want to measure 10-20cm distances using a 40k CT10U-30S400-1 transducer rated at 10V and C=10nF.

I am using mode 0 of the TDC1000 with the settings in the screenshot below. Unfortunately I cannot get an echo and the TX signal rings and then is pulled up to some DC level it seems.

I have made the following mods on the EVM:

- Changed filter to include only an RC low pass with 100kHz cutoff (100R, 15nF)

- Changed to use external clock set at 1.28M --> 1.28M/32 = 40k

- Changed series resistors on TX path to 500R

- Replaced RX paths series capacitors to resistors of 1K. (for LNA gain of 9)

See images below:

The setup. Distance to box is never detected no matter what settings are used, tried bypassing the LNA, PGA, changing gains, timing. What am I missing? Does anything on the evalboard need to be changed? Is a simple low pass filter not enough and should I implement a bandpass?

Using CT10U-30S400-1 . Yellow is the buffered COMPIn signal. on the EVM. Blue is directly on the TX output with transducer connected. Purple is start line.

Using a different 40K transducer:

Changes made:

  • 0 in reply to Sam Sulaimanov
    TI__Mastermind 23045 points

    Hello Sam,

    Thanks for posting to the sensors forum!

    Typically we don't recommend using TDC1000 for 40kHz operation. There are a couple if items that make it hard to operate this device at lower frequencies so we only recommend the use of this device for water coupled applications and at higher frequency ranges 500kHz and up.

    One problem being that setting up the external filters can be somewhat challenging, but the main issues are related to the drive voltage of the transducer and this devices low dynamic range compared to some of our other devices like PGA460 or TUSS44x0. These other devices have a large dynamic range when compared to TDC1000 which makes them more suitable for operation over the air. The TDC1000 can only drive the signal at 5V which means you wont be able to get much energy out the signal and combined with this devices dynamic range it will be difficult to detect the echo signals.

    Here is an FAQ we wrote to help you select an ultrasonic sensor AFE for various applications: https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/748143/faq-ultrasonic-sensors

    Let me know if you have any questions I might be able to help out with.

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 10 points

    Hi

    Thanks for the reply. The transducer I used is 10V nominal, so 5V actuation should be fine.

    The EVM manual clearly states that TI recommends 2 types of 40K transducers for operation with TDC1000. Could you please advise if they have been ever made to work with the TDC and what configuration was used?

    Thanks

    Sam

  • 0 in reply to Sam Sulaimanov
    TI__Mastermind 23045 points

    Hello Sam,

    The transducers listed on the users guide have been made to work with the TDC1000, unfortunately I am not certain what configuration were used for this operation. The TDC1000 provides only about 21dB of gain which is not very much for air coupled applications and hence why we only really recommend it for transducers at higher frequencies for liquid coupled applications. The 5V signal creates very little sound pressure, so the signal attenuates fairly easily over the air and with the small dynamic range this device does not operate well over the air. I strongly recommend the use of another device if the goal is to use a 40kHz transducer. If you need more help on setup there are some recommendations in this thread: https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/924551/tdc1000-q1-received-signal-very-poor-or-not-there-at-all

    If you setup your filters correctly its possible that the configuration for the echo listening window may be incorrect, so please ensure that the device is checking for echoes at the right time. Probing the COMPIN signal will give you visibility if you are getting a return echo on the transducer. Another recommendation would be to increase the number of pulses transmitted during a burst, this will help you increase the energy transmitted and increase chances of detection, this can help you determine if your configuration is working correctly. If you need assistance configuring the echo listening window please provide some info on detection range I can help ensure your settings are correct.

    Best,

    Isaac