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TDC1000: My echo was lost! i can't see anything in the COMPIN. What did i do wrong?

Alberto Roura
Prodigy 50 points
Part Number: TDC1000

Hi everybody, 

i'm designing a tank level sensor, all works fine apparently but i cant´t see any signal in the compin.

The circuit is:

*CLKIN : 5MHz     *Transducer: 40Khz

*Bandpass between PGAOUT and COMPIN: 22KHz(2.2nF, 3.3Kohms)-72.3KHz(.01uF,220 ohms)

*Between LNAOUT and PGAIN: 1nF

*LNA =Resistive

*PGA Gain: 21dB (already probe all gain values)

*Tx: 30 pulse

*Mode: 0

*Short TOF

the exact value of the registers are : CONFIG0: 0xDE, CONFIG1: 0x40, CONFIG2: x80, CONFIG3: 0x00, CONFIG4: 0x5F, TOF_1: 0xE4, TOF_0: 0x1F, TIMEOUT: 0x43, CLOCK_RATE:0x00

i need do the measurement in a range of 5 cm - 50 cm, any idea? Sorry if my english is not the best, i'm learning.

Any help is appreciated.

  • 0
    Prodigy 50 points

    YELLOW = COMPIN

    BLUE = Tx

  • 0 in reply to Alberto Roura
    TI__Mastermind 31655 points
    Hi Alberto,

    Since you are using a TX pulse setting of 30, the time that the sensor is transmitting is quite long (it looks to be roughly 700-800us from the scope capture). In addition to this, there is the small amount of ringdown time from the transducer, which is about another 200-300us. In water, the speed of sound is about 1350, so assuming you are measuring from the bottom of the tank through water, this transmit time will account for about 1.35m of total travel, or 67.5cm one way which is greater than your max tank level. If this is the case, then your echo is masked inside the transmit pulses.

    I suggest reducing the number of transmit pulses to 5 or less. Especially at a lower frequency like 40khz there should be little attenuation through such a small distance.

    Additionally you have FORCE_SHORT_TOF enabled. In this case you should disable it since you have a fairly long time before an expected echo.

    However, you should still see some activity on the COMPIN pin during this time. Could you please upload a schematic of your setup?

    Regards,