My problem is that I have 2 Arduino Uno's hooked up to 3 different hc-sr04 sensors. One of them is a transmitter and the other two are receivers. I need the receivers to be able to read the ping from the transmitter. This is easier said than done because usually one sensor will send out and receive the ping therefore being able to tell distance. Since the receivers and transmitter in my setup are not connected, I do not know what to do. My first instinct was have one Arduino have the transmitter pinging on a loop and the other Arduino always listening for pings. This does not seem to work so could someone please shed some light on what I can do?
What you want to do is not an option with the HC-SR04. The receivers need to be independent and google will provide schematics and/or instructions on how to make them. It seems possible that someone has hacked the HC-SR04 to separate the transmit and receive functions, or at least you could reuse the parts. Here is a potentially useful link identification - Can anyone identify the microcontroller on an HC-SR04 - Electrical Engineering Stack Exchange
If you intend to use time-of-flight to measure distances, then you have another problem: how will the receivers know when the ping was originally emitted by the transmitter?
Hi abomb,
maybe it is too late, but you can do it with a fairly-simple hack (you will need 3 xbee radio).
You just need to make the the transmitter to send a radio packet whenever it triggers the hc-sr04 pin. This radio packet is then used by the 2 receivers to trigger their hc-sr04 sensor (resulting in a synchronous distance estimation on the 3 hc-sr04)
If transmitter and receivers are facing each other, the receivers will first receive the transmitter ultrasonic wave rather than their own (that has to travel back and forth). Thus, the receiver's will estimate half of the distance between the receiver and the transmitter (the circuit gives for granted that the received signal is not direct but it is an echo).