Issue
150 January 2003
The
PSoC RangeFinder
A
Simple Ultrasonic Distance Meter
by
Fabio Piana
Some distances are more difficult
to measure than others. Therefore, Fabio built his
own ultrasonic rangefinder, which won First Prize
in the Cypress PSoC design contest. It can be used
for measuring liquid levels, generic distances,
and even the depth of snow.
Start
•
Micro Configuration • The
Hardware
• Practical Construction
• Things To Consider •
Sources and PDF
There
are several ways to measure distance without contact.
Some products have infrared light emitters and receivers
that determine an object’s distance by implementing
the optical triangulation method. Other devices have
laser-based systems that increase accuracy and precision.
For electrically conductive metal objects, the eddy
current method is an option, and capacitive sensors
that are independent of the metal used in the measured
objects can be used.
I
decided to use ultrasonic waves. My ultrasonic PSoC
RangeFinder measures the amount of time it takes for
a pulse of sound to travel to a particular surface and
return. Then, the device calculates the distance based
on the estimated speed of sound. In this article, I’ll
explain how I built this simple ultrasonic distance
meter.
Photo
1a is a picture of my PSoC RangeFinder with an LCD.
The display is optional, and I removed it for Photo
1b. For this particular application, the only required
components are a PSoC microcontroller, two 40-kHz ultrasonic
transducers, two resistors, and two capacitors. Similar
circuits are typically complicated and expensive, consisting
of a large number of integrated circuit and passive
components.
|
(Click
here to enlarge)
|
Photo
1a—There are several things to consider when building
your own ultrasonic rangefinder, including whether
or not to incorporate an LCD. b—Take a look at the
PSoC RangeFinder without the LCD. |
Take
a look at the RangeFinder’s system block diagram in
Figure 1. As you can see, it’s divisible into three
parts: the transmitting section, receiving section,
and output section. Each section contains several PSoC
blocks. Using the PSoC chip family, all of the digital
and analog devices are on-board with the microcontroller.
|
(Click here to enlarge)
|
Figure
1—There are three distinct sections in my PSoC RangeFinder
project: digital blocks, analog blocks, and transducers. |
The
RangeFinder has numerous applications. You can use it
for the positioning of robots as well as measuring generic
distances, liquid levels in tanks, and the depth of
snow banks. The device can also serve as a motion detector
in production lines where surfaces must not be damaged,
or you can use it for educational purposes.
A
restricted target angle (it requires a near-perpendicular
surface) and large beam, which can create poor resolution,
seem to be the RangeFinder’s only limitations. Despite
these drawbacks, you’ll find the device’s main features
to be extremely useful.
The
RangeFinder has a 40-kHz operating frequency, a range
of 25 to 200 cm, and 1-cm resolution. In addition, it
requires only a single 5-VDC power supply and draws
just 25 mA (23 mA without the LCD). The device has one
PWM output and one TTL-level serial output (9600 bps,
8 bits, 1 stop bit, and no parity). Finally, don’t forget
the optional 2 × 16 LCD, software calibration, and dynamic
receiver stage gain increment.
