Issue 150 January 2003
The PSoC RangeFinder
A Simple Ultrasonic Distance Meter

THINGS TO CONSIDER

I used the 28-pin CY8C26443 microcontroller because of its availability; however, you can use the eight- (if you don’t use the LCD) or 20-pin versions for a smaller PCB. With the LCD connected, you can display useful information while setting up and calibrating your own PSoC RangeFinder.

It’s easy to change the program if you’re thinking about modifying the device’s behavior. Because any one of several obstacles can surface at any time, the ultrasonic distance meter can make mistakes during the measurement process. However, if you want to prevent measurement errors, you can modify the software to calculate the average value of several measurements and discard the measured values that are out of range.

The measurement process is based on a typical air temperature of 22°C. This can be limiting when the specific application involves a wide operating temperature range.

If you use a 28- or 20-pin integrated circuit, there will be a lot of free pins in the PSoC microcontroller. It would be an improvement to implement an external integrated temperature sensor to measure the air temperature. Because of its low accuracy (± 20°C), the internal FlashTemp module isn’t suitable for the job. But, if you want to increase the precision, you can calculate and compensate for the different sound velocities at different air temperatures.