# Increase amplitude of ultrasonic transmitter

I'm currently working on a project where I want to send an ultrasonic signal from one Teensy 4.1 to another. To do this I've taken a US-100 ultrasonic module apart so that I only have the transceivers.

I've got it working but I'm only getting a small signal on the receiving end (I have created a gain to boost the signal.)

My problem is that if I send a signal from another US-100 at the same distance as my transmitter, I get a stronger signal at the receiver. This got me thinking that the US-100 is producing a higher amplitude than my transmitter circuit. I might have a bad circuit since I don't know much about electronics and how the fundementals work - just found some basics on Google.

See my circuit:

I've tried swapping the 180ohm resistor with both smaller and larger (smaller seemed to reduce the amplitude of the receiver - tried 20ohm.)

Is my circuit completely off? Am I doing something wrong, or is it other factors that play in here? The US-100 is also powered by 3.3V so it might not seem like a voltage problem. I'm creating a square wave. Based on my oscilloscope the US-100 is around 39kHz and my setup is at 38,76kHz - which I don't think makes a difference. They are the same transceiver since I took it off another US-100 module. Both doing 8 pulses.

I'm pulling Pin14 high with this code:

for (int i=0; i<8; i++) {
digitalWrite(TrigPin, HIGH);
delayMicroseconds(12);
digitalWrite(TrigPin, LOW);
delayMicroseconds(12);
}


When measuring on the transceiver (directly on the transceiver and ground),) they both are HIGH and pulled LOW the 8 times, where I afterwards can see the amplitude of my transmitting is higher than on the US-100. In the following pictures you can also see the difference in received signal (teal color.) Bear in mind that the transmitter was placed at the same distance from the receiver in both results.

Yellow = Transmitter