HC-SR04 Isn’t The Same As Parallax PING))) But It Can Pretend To Be!

“It’s only software!” A sentence that strikes terror in the heart of an embedded systems software developer. That sentence is often uttered when the software person finds a bug in the hardware and others assume it’s going to be easier for fix in software rather than spin a new hardware revision. No wonder software is always late.

[Clint Stevenson] is his own hardware and software guy, as are most of us. He wanted to use the less expensive HC-SR04 ultrasonic rangefinder in a prototype. Longer term he wanted to have the choice of either a Parallax PING or MaxBotix ultrasonic sensor for their better performance outdoors. His hardware hack of the SR04 made this a software problem which he also managed to solve!

[Clint] was working with the Arduino library, based on the Parallax PING, which uses a single pin for trigger and echo. The HC-SR04 uses separate pins. Originally he modified the Arduino library to accept the two pin approach. But with his long term goal in mind, he also modified the HC-SR04 sensor by removing the on-board pull-up resistor and adding a new one on the connector side to combine the signals. That gave him an SR04 that worked with the single-pin based library.

We’ve seen Parallax PING projects for sensing water depth and to generate music. These could be hacked to use the HC-SR04 using [Clint’s] techniques.

[Arduino and HC-SR04 photo from Blax Lab]

8 thoughts on “HC-SR04 Isn’t The Same As Parallax PING))) But It Can Pretend To Be!

  1. You can choose between the one or two pin approach with the HY-SRF05 Ultrasonic sensors which cost roughly the same as the HC-SR04, so it seems a little odd to hack the SR04 instead of picking up the SRF05. I’m going to guess this was someone who already had a stack of SR04’s laying around.

  2. Last time I used an HC-SR04 with a Teensy, I just wired the TRIG and ECHO pins together and told the NewPing Arduino library to use the same pin for both functions. I’m not sure where I read about that trick, but it worked for me.

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