It's not calculated at all, just a random value, massively higher than it needs to be - it's only got to pass 40KHz.
The impedance of the sensor is a lot higher than that, and it's a poor design because it's presenting far too low an impedance to the sensor (only 2K2).
I do not know what C6 and R7 do, and how effect the circuit and how there values are chosen?
It's not calculated at all, just a random value, massively higher than it needs to be - it's only got to pass 40KHz.
The impedance of the sensor is a lot higher than that, and it's a poor design because it's presenting far too low an impedance to the sensor (only 2K2).
It's a timing circuit, to slow down the comparator been enabled after the pulse has been sent.
Thanks a lot, yeh I was told by somone else to stick another 10000ohms on the impedance in - its like they havent taken into acount the transducer input impedance - eventhough that schematic is from a on sale sensor!
Didnt have a clue about the timing circuit! Cheers
Thanks a lot, yeh I was told by somone else to stick another 1000ohms on the impedance in - its like they havent taken into acount the transducer input impedance - eventhough that schematic is from a on sale sensor!
It's not a question of an extra 1000 ohms, you really need in the 100's of thousands, or the millions. That's why you would use non-inverting mode rather than inverting mode.