The SRF01 is a popular ultrasonic sensor used primarily for range finding applications. [Jaanus] discovered that they had a few flaws, including not working after being dropped. The faulty ones began to pile up, so he decided to tear one apart and put his engineering skills to use.
The SRF01 is unique in that it only uses a single transducer, unlike the SRF04, which uses two. Using only one transducer presents a problem when measuring very close distances. The transducer emits a pulse of sound and then must listen for the echo. The smaller the distance, the smaller the time interval between the pulse and when the echo returns. There is a fundamental limit to this time as the transducer has to recover from what is known as ringing. [Jaanus] discovered that the SRF01 solves the ringing problem with the use of a PIC24’s ADC and its 500 ksps (kilosamples per second) rate. This allows it to measure very close distances.
Be sure to check out the teardown for more details on how the SRF01 works.
“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]
[Emil] got his hands on a dozen HC-SR04 ultrasonic sensors, but wasn’t too happy with their performance. Rather than give up, he reverse engineered the sensor and built an improved version. Hackers, Makers, and robotics enthusiasts have had easy access to standard sonar platforms since the early 1980’s, when Polaroid began selling their 6500 sonar modules. A number of companies have released sonar boards since then, notably The Parallax Ping))) module. The HC-SR04 appeared on the market a few years back as a low-cost alternative of the Ping.
[Emil] found that the HC-SR04 would work reliably on hard surfaces as far as 4 meters away from the sensor. However, he got a lot of bad data back when using soft sided targets, or when no target was present at all. [Emil] reverse engineered the schematic of the HC-SR04 and found some interesting design decisions. A Max232 RS-232 converter chip is used for its
+-12V +-10V charge pumps. The charge pumps are connected to create 24V 20V at the ultrasonic transmitter. A mask programmed microcontroller manages the entire unit, commanding the ultrasonic transmitter to send 40Khz pulses, and listening for returns on the receive side of the system. [Emil] believes the micro is running in polled mode, due to the fact that it sometimes misses pulses. Even worse, the micro runs on an unmarked 27MHz crystal which had quite a bit of drift.
[Emil] solved these problems by creating his own PCB with an ATtiny24 and a 12MHz crystal. He increased the pin count from 4 to 6, allowing the ATtiny to be programmed in circuit, as well as opening the door to I2C and SPI operation. To build the boards up, [Emil] first solders his micro and crystal. He then uses a hot air gun to move all the components from the HC-SR04 board to his own. The new boards are still being tested, but [Emil] has posted his PCB and BOM data. He’s also promised to post his AVR code when it is available.
[Rick], an Adafruit learning system contributor, is excited by the implications of STEM’s reach into K-12 education. He was inspired to design Red Rover, a low-cost robot that can be easily replicated by anyone with access to a 3-D printer.
This adorable autonomous rover is based on the adafruit Trinket microcontroller, but will also rove under the power of an Arduino micro. It really is quite simple—the Trinket drives two continuous rotation micro servos and pretty much any flavor of rangefinder you like. [Rick] tested it with Parallax PING))), Maxbotix, and Grove sensors, and they all worked just fine.
What’s truly awesome about Red Rover are the track treads. [Rick] initially experimented with flexible filament. While he had good results, it was not a cost-effective solution. What you see in the picture and the short video after the break are actually rubber bracelets from Oriental Trading.
The plastic part count comes in at seven, all of which can be printed together at once. [Rick]’s gallery includes both small and large chassis and three different servo mounts. The Red Rover guide builds on other adafruit guides for Trinket general use, servo modification, and Trinket-specific servo control.
Update: Added [Rick]’s demo video after the break!
Continue reading “Mustachioed Rover Simultaneously Manly, Adorable”
Ideally, technology is supposed to enhance our lives. [Shane and Eileen], two seniors at Cornell have found a great way to enhance the lives of visually impaired individuals with their acoustic wayfinding device. In brainstorming for their final project, [Shane and Eileen] were inspired by this Hackaday post about robots as viable replacements for guide dogs. They sought to provide wearable, hands-free guidance and detection of (primarily) indoor obstacles—namely chairs, benches, and other inanimate objects below eye level.
The wayfinder comprises two systems working in tandem: a head-mounted navigation unit and a tactile sensor worn on the user’s finger. Both systems use Maxbotix LV-MaxSonar-EZ0 ultrasonic rangefinder modules to detect obstacles and vibrating mini-disc motors to provide haptic feedback at speeds proportionate to the user’s distance from an obstacle.
The head unit uses two rangefinders and two vibrating motors. Together, the rangefinders have a field of view of about 120 degrees and are capable of detecting obstacles up to 6.45 meters away. The tactile sensor comprises one rangefinder and motor and is used in a manner similar to a Hoover cane. The user sweeps their hand to detect objects that would likely be out of the range of the head unit. Both parts are ergonomic and size-adjustable.
At power up, [Shane and Eileen]’s software performs a calibration of the tactile sensor to determine the distance threshold in conjunction with the user’s height. They’ve used an ATMega 1284 to drive the system, and handled real-time task scheduling between the two subsystems with the TinyRealTime kernel. A full demonstration video is embedded after the break.
Continue reading “Acoustic Wayfinder for the Visually Impaired”
Let’s start off with some high voltage. Here’s a sweet Jacob’s Ladder build from [Robert]. The site hosting his short writeup has been up and down for us so here’s a cache link.
Speaking of high voltage, if you want to switch mains with your project [Tom] has a breakout board for cheap mechanical relays. [via Dangerous Prototypes]
[Dario] made his own version of an electronic Advent calendar [translated]. There are no numbers, you must solve the mystery of the flashing LEDs to figure out which package goes with each day.
If you ever work with lighted arcade buttons here’s a guide for swapping out the light for an RGB LED. This hack uses through-hole LEDs. We’ve actually seen a surface mount hack that includes a PCB to mimic the old bulbs.
Next time you stay overnight at an event you can give yourself the best view in the campground. This tiny little camper was mounted on a scissor lift! That first step on the way to the Porta Potty is a doozy! [via Adafruit]
[Žiga] was nice enough to demonstrate this smart-watch hack by displaying our name and logo (we love pandering!). It features the MSP-WDS430 which is a surprisingly stylish offering from Texas Instruments. In addition to analog clock hands it has an OLED display driven by the MSP430 inside.
Here’s a quick PIC-based metal detector which [Nicholas] built.
And finally, [Chet] saw the oil tank level sensor we featured this week. He built a nearly identical system earlier this year. The oil level sensor works in conjunction with the custom thermostat he built around an Android tablet.
[Klaus] wanted some sort of aid for parking his car, and after running across a $4 ultrasonic sensor, decided to build his own speaking distance sensor (.de, Google Translation).
Inside [Klaus]’ device is an Arduino Uno, an HC-SR04 ultrasonic distance sensor, and an Adafruit Wave Shield. Originally, this parking/distance sensor used a small TFT to display the distance to an object, but after a few revisions, [Klaus] redesigned the device to speak the current distance, courtesy of an SD card and a soothing female voice.
Right now, the voice is set up to speak the distance from an object to the sensor from 10 cm to 1 m in 5cm increments. This isn’t the limit of the sensor, though, and the device can be easily reconfigured to sense a distance up to four meters.
The board doesn’t have an amplifier or speaker, but with the addition of a small amplifier, [Klaus]’ device is loud enough to be heard in even the noisiest environments.
Video demo below.
Continue reading “A Speaking Ultrasonic Distance Sensor”