Ultrasonic Transmitter Issues

[tw0081]

Hi there,

I'm creating an ultrasonic transmitter and reciever. I have created two different transmitters so far and have posted both circuit diagrams below. I am trying to transmit a constant 40kHz signal, but without a osc I can not be sure if both these astables are going low. At the moment I have a constant voltage from my multimeter on the output pin.

Please could someone tell me how to create a reciever, and if they believe these transmitter circuits will work?

Also, the slanted picture is from a datasheet, and the other is one I have devised and built.

Thanks for your help.

 

[audioguru]

Your resistor values are very low which causes very high currents which is wrong.
Instead of 47 ohms use 4.7k ohms.
Instead of 147 ohms use 15k ohms.
Then reduce the value of the 100nF capacitor to about 1nf.

A multimeter measures average DC or the 50Hz or 60Hz mains frequency voltage. It cannot measure the 40kHz output level, use an oscilloscope instead.