Ultrasonic module customization ideas

Projects / Project Swiftlet  

Possible Customization

U1 can be implemented inside the ARM MCU (Freescale MKL16) by using a PWM output. The same analog signal block for processing the received signals from transducer can be shared by multiplexing the left and right inputs. The new opamp should work fine at 3.3V, so not have to worry about voltage tolerance. U2A block can be implemented in the CMP (Comparator) block inside the MCU. There is an internal 6-bit DAC that can be used to dynamically reduce the threshold over time. The output of the comparator have to be routed outside the MCU to a pin and back to the input capture of the timer (TPM). The analog signal can also be fed into ADC for sampling to extract the amplitude and timing of the return echo envelopes.

Have to think about the Ultrasonic driver circuit and also see if I can somehow use 1 single transducer for both Tx and Rx to reduce size and weight. This application would not require very close distances so 2 transducers is not needed

Spoiler: Sadly, I found out much later on that the comparator isn't that fast.  Single transducer idea didn't pan out as the sensors I have is quite bad - well they are cheap.

Saw a HaD link to SparkFun ToF Range Finder Breakout - VL6180 which is interesting. The more interesting part is the ad for the related product at the bottom: Ultrasonic Range Finder - LV-MaxSonar-EZ0 The module is using a single ultrasonic transducer for both transmit and receive. It claims that it can be used from 6 inches up and run from 2.5V to 5.5V at 2mA.

6 inches ~ = 6 in / 13386 in/s = 448us. So that's the upper limit of ringing on their transducer

The module however is not open sourced, so I probably won't be using it in the product. It does offer some hope. Whether the unknown transducers they used in the Chinese modules have necessary damping in it for half duplex, I'll have to find out when it arrives in 2+ weeks. I'll probably need to do some measurements.

Interesting links:
http://www.ele.uva.es/~jesus/sonar/sonar.html Single transducer design
http://robotang.co.nz/projects/electronics/ultrasonic-rangefinder/ Also single transducer design
http://www.shapeways.com/product/CYX7H44HZ/ping-ultrasonic-range-finder-range-extender

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Found the old ultrasonic range finder I built back in the university days. The transmitter signal is generated from a quad NAND as an oscillator, and driven from with a pair of push pull transistors and step up transformer. The receiver amplifier is out of 4 discrete transistors I probably didn't design that receiver. It has some sort of gain control stage. The amplified signal is fed into a NE567 tone detector.

The transmitter has a piece of tape over the transducer probably for damping out the ringing.

The size is That was built long before I had schematic capture and layout tools, so the schematic is probably sitting somewhere in my pile of hand drawn schematic. These days I do a schematic and layout for most projects.