Excelity 3pcs Ultrasonic Module HC-SR04 Distance Sensor with 3pcs Mounting Bracket

I bought these devices as replacements for a robotic car (Picar-X) which also came with an HC-SR04. However none of these devices worked in this application - it turns the Picar-X delivers 3.3V to the HC-SR04 where every HC-SR04 device I've encountered run at 5V. Apparently the makers of Picar-X use a 3.3V variant or perhaps they modified a stock HC-SR04.Subsequently I attached each sensor in turn to my raspberry pi (running the Bluetin_Echo library) and found all three devices worked perfectly.Important to note the pi gpio pins work at 3.3V whereas the HC-SR04 works at 5V so be sure to use a resistor step-down on the 'echo' output going from the HC-SRO4 into the pi gpio pin (the 'trigger' input works fine at 3.3V).The HC-SR04 generates a return pulse (on the echo pin) whose width is proportional to the measured distance. Determining the length of this pulse can be problematic because the pulse width is measured in mere micro-seconds. Computers such as the Raspberry P, running a relatively sophisticated operating system, are not optimized for high-accuracy timed interval measurements. So you should expect to see jitter and the occasional false reading.If you want a more accurate and more consistent sensor, consider devices which return numeric distance values across RS232 TTL or I2C bus (such as the HRLV-MaxSonar-EZ1).Okay, so the sensor were all good and worked fine. The plastic frames aligned perfectly with the transponders and are an easy slip-on fit. I used a dab of epoxy to secure the sensor to the frame.These devices are dependent on the speed of sound which varies with temperature. You need to be aware of this limitation which is shared by all (non-compensated) ultrasonic transducers. I typically calibrate and map these devices over a range of distances (in software) and use a temperature sensor to adjust for the prevailing speed of sound. Even so, these aren't super accurate devices. However they are excellent value for money and for simple robotics are highly effective. For more sophisticated robots I use stereo cameras and lidar - neither of which are cheap!For the Raspberry Pi I used the Bluetin_Echo library to run the HC-SRO4. Effortless solution.So, overall I consider this was a good buy and I'm a satisfied customer.

I used this on a robot to create a distance feedback loop and it worked perfectly when the system was steady. During calibration (with the system being still) the measurements retrieved from the sensor were identical to the measurements taken in person with a ruler. However, once the mechanical system started up, the measurements were a little off and sometime it would turn off while it steadied itself again. This was an easy thing to fix by writing into the code lines with a significant range of distance rather than targetting precise measurements for the system to work.TLDR: Great for systems with little to no vibrations, otherwise you might have to play around with it to make it work, but not impossible.

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I think I got these for a bargain. Make sure you connect them to 5V and use 330 Ohm resisters for the echo despite most tutorials claim they work on 3.3V.These have been working flawlessly and very accurately on automatic door slider for my house sensing close bodies on both sides of the door. Funny how educational grade modules and sensors can actually serve so much for so long.

Used to determine level of food in animal feeders

I have an older one stuck into a breadboard, so it was easy to run all 3 and they all showed 1 µs or 0 distance. I popped the old one in alternately and it read what it always does in this rig.I didn't see or smell anything odd. For what it's worth the new ones look great and have fewer components than the old one.They are "unavailable now" so I'll try for a refund and buy more elsewhere

The sensor delivers unreliable distance. It will read distance about right but as soon as you put the object or sensor at a 10 degree angle, the readings are all over the place. Don't bother.

These are Standard SR04 sensors that employ separate transmit and receive transducers and are well-suited for robotics. They also come with brackets which are a nice touch.My only issue with them is that having modified them for use in an environment where the temperature varies considerably, I found that 10 microseconds was not long enough to get the sensors to start reliably over temperature and supply voltage. This has been reported in literature elsewhere, although not in relation to the environment as far as I know. Nevertheless, that is still something you should know.Their limitations notwithstanding, I do recommend them.