Kevin Gallagher said:
Hello,
I'm building an ultrasonic tape measure and am having trouble obtaining a distance greater than 1 metre. I have an idea to try and get a greater distance: I think that maybe I am losing a lot of my transmitting power because the output impedance of my oscillator is not matched well enough to ultrasonic transducer and similarily at the reciever.
The oscillator is the 4047BE and in the datasheet there is no talk of output impedance. Does anybody know what it is or how i could find it. The o/p of osc is fed directly to transducer which is SCS-401T. At the reciever the rx transducer (SCM-401R) is fed directly through a capacitor and then to a 10k resistor which is the input resistor for the amplification stage.
On the datasheet for the transducer it says the impedance is approx 500 ohms for txer and 30 kohms for the rxer. Is this the same value for i/p and o/p impedance cos it just says impedance.
I would really appreciate any help anyone could offer me.
Thanks
The 4047 bloack diagram shows a buffered output so you can assume it is very low, maybe less than 1 ohm.
To match, determine what your Tx input impedance is, and then put the same value of resistor in series with the output of the 4047. If your line length is very short (from OSC to Tx) this will work OK. If your line length is longer (how much depends on rise time of signal) then you will have to build a transmission line interfacing the two.
Keep in mind, this method will match your OSc-out to Tx-in but will be attenuated by 50% (the matching resistor forms a divider) but it should be undistorted at the receiving end (and hence your will not be losing power output due to mismatch anymore) You may want to buffer the OSC with something that can give you higher volts so that you can keep the Tx power out the same.