I am creating an ultrasound time of flight system and am currently in the testing phase. I am using a TDC1000-TDC7200EVM board from TI for testing.
Currently, I have a 40 kHz ultrasonic transducer. My test board comes with a 8 MHz clock preinstalled. Given the divider values available (powers of 2), the closest output frequency I can get for the transducer is 31.25 kHz.
My idea is to use the PWM output from ATmega chip on an Arduino to generate an external clock source for the TDC board. I can generate 2.67 MHz PWM, then the TI board can divide that by 64 to get 41.7 kHz output.
My question is: How can I connect the PWM to the TI boards external clock pin?
Since the ATMega operates at 5V and the TI chips are 3.3V, I tried using a voltage divider to get a 3.3V PWM signal. However, this behaves in an unexpected way. I am using 330kΩ and 680kΩ in series. After the 330 kΩ resistor, by signal drops to ~30 mV peak-peak.
If I use smaller resistors, 3.3 kΩ and 6.8 kΩ, I get ~640 mV peak-peak, but the signal looks like a triangle wave instead of square wave.