Can I use lengthy wire?

[milan.rajik]

I have done a Ultrasonic distance measurement project using SR-04 and Arduino and it is working as expected and detecting upto 440 cm precisely. Arduino digital IO pins can source or sink 40 mA. I want to know can I use a 4 X 30 feet wire for the sensor (VCC, GND, Trig, Echo) because I have to sense the distance of an object which is 30 ft from the device which has to be controlled depending upon the distance. The sensor is used only to measure 4 ft.

 

[BradtheRad]

Electricity travels almost a million times faster than sound.

You would need 4400 km of wire, to create an electrical delay equal to that of sound traveling 440 cm. And even longer wire if you are talking about 30 ft.

I'm not sure if this is the sort of answer you were looking for.

 

[milan.rajik]

Mo, not about delay. I wanted to know will the sensor (Ultrasonic) give precise value if lengthy wires are used. Also can I power the Sensor with two wires at the sensor end and only run 2 wires (Trig and Echo) from Sensor to Arduino. Will this work?

 

[BradtheRad]

When you transfer signals over long runs of wire, it is important to minimize the influence of hum and noise and static charge.

You need a shielded cable. Its ordinary name is 'microphone cable'. I believe your ultrasonic transducer is not too different from a microphone.

Your loop which carries the signal (namely the signal wire and ground wire) should not have an extremely high impedance. A lower impedance has the advantage of reducing noise and hum and static charge. But avoid making it so low that you attenuate your signal by too much.

 

[FvM]

You'll use at least individually shielded cables for trigger and echo signals. A series termination (50 to 100 ohms) on the driver side should be provided to reduce signals reflections. Ultimately you'll convert the singled ended logic signals to differential on the driver and back to single ended on the receiver side, and transmit it through terminated twisted pairs, e.g. CAT5 ethernet cable.

 

[milan.rajik]

Can you provide a sample circuit?

 

[D.A.(Tony)Stewart]

Ultrasonic sensors are usually piezoelectric and reduce their sensitivity with capacitive loading from long cable. Therefore you need to figure how to buffer received high impedance signal remotely.

 

[FvM]

Ultrasonic sensors are usually piezoelectric and reduce their sensitivity with capacitive loading from long cable. Therefore you need to figure how to buffer received high impedance signal remotely.

Yes, but SR-04 is a sensor unit with a digital interface (TTL/CMOS level). In so far the problem in this case is reliable transmission of medium speed (10 µs range) pulses.

Can you provide a sample circuit?

You can use e.g. SN75179 (Differential driver and receiver pair) at both sides, RJ45 network cable, two twisted pairs for signal transmission, third and fourth pair for power supply. Both signal pairs with 100 ohm termination at the receiver.

 

[milan.rajik]

First I will see what happens if only shielded wires are used. 2 pairs, TRIG+GND and ECHO+GND. Later I will use drivers because if I use drivers then I have to make another circuit, PCB and provide power supply to SN75179 at the sensor end. I have two such sensor. So, I have to use 4 X 75179. The cost will become high. I am using it to sense fluid level. I tested with water and it works fine. It gives the right distance.

I think it is better to make the system wireless using Arduino Nano V3.0 + ITEAD Nano XBee shield + XBee PRO module. This way I can eliminate lengthy wires and drivers. A Li-Po battery will power the system at the 2 tanks and two Nano's will send the data to master receiver board which is Mega 2560. The Mega will control the pumps.

 

[milan.rajik]

I found this. Can I use this instead ?

https://www.banggood.com/5V-MAX485-TTL-To-RS485-Converter-Module-Board-For-Arduino-p-912674.html

 

[FvM]

You'd need two pairs of RS485 converters to transmit the trigger and echo signal, or use additional logic to route both signals through a single half-duplex connection.

 

[milan.rajik]

If I use the above module (2 nos.) how should I connect the US Sensors to it and also how to interface it to Arduino. Please provide the wiring diagram.