A close-up view of the end of an antenna element.
The wire was wrapped around a small jeweler’s screw
driver and then soldered.
Group, I got a chance to see one in action. To date, I’ve
used them to send commands to robots and to receive data
from wireless dataloggers. Therefore, I’ve just begun to
scratch the surface of their potential. These radios are
complete, so all I had to do is create the support board
for them.
There are two jumper wires for this PCB and cut
resistor leads are perfect for them. Bend the leads of the
transmitter and receiver to a 90 degree angle and solder
them to the PCB. The crystal and IC side of the transmitter
and receiver boards will be on the outside, allowing them
to sit nearly flush to the PCB.
The simplest antenna is the dipole, or two element
antenna. To reduce the vertical height of the radio PCB,
one of the elements is replaced with a ground plane.
What’s the proper length for each of the antenna
elements? Well, it’s not simply the longer the element, the
better. Radio antenna elements are more efficient when
they are resonant at the frequency they are being used at.
This resonance occurs when the length of the element is
an odd multiple of half of a wavelength. However, since
current doesn’t flow at the speed of light through a
conductor, we have to incorporate the velocity factor
into the length of the antenna element. Amateur radio
operators use the following equation to calculate the proper
length of their dipole antennas:
Length (feet) = 486/frequency (MHz)
Using this equation for a SparkFun 434 MHz
transmitter and receiver, I get 486/434 or 1.12 feet.
Since each antenna element is half the total length of the
antenna, I divide 1.12 feet by two and convert the length
into inches to find that the 434 MHz transmitter and
receiver should have antenna elements 6. 7 inches long.
There are six antenna elements on the radio PCB: four
for the ground plane and one each for the transmitter and
receiver. Now, in reality, you can skip the four ground plane
elements like I did in the parts placement diagram of the
radio, but the radio should work better if you include them.
The two silver dots in the drawing represent the other two
56 SERVO 08.2009
LINE FOLLOWER PARTS LIST
ITEM
❑ Line Follower PCB*
❑ Two 330 ohm resistors
❑ Two 47k ohm resistors
❑ Two IREDs**
❑ Two Phototransistors**
❑ Wire (#24 AWG, four different colors recommended)
❑ 2x3 Header
❑ Thin heat shrink
❑ 1/4 inch diameter plastic tube (available at hobby stores)***
❑ Aluminum duct tape (available at home improvement
stores)***
❑ 1/2 inch thick Styrofoam****
❑ Hot glue
*Use the pattern included in the download for this article to make
your PCB.
**Available individually from Jameco or as a pair from RadioShack
(276-142).
***You can substitute 1/4 inch diameter aluminum tubing and skip
the aluminum tape.
****I recommend 10 mm thick Cellfoam 88 (available from hobby
and arts and craft stores).
PROXIMITY DETECTOR
PARTS LIST
ITEM
❑ Proximity Detector PCB*
❑ 270 ohm resistor (2)
❑ 330 ohm resistor
❑
4.7K ohm resistor
❑
6.8K ohm resistor
❑ 100K ohm resistor
❑ 5K ohm trimmer
❑ 0.001 µF (1 nF) capacitor
❑
4. 7 µF electrolytic capacitor
❑ 14-pin DIP socket
❑ 74HC04 hex inverter
❑
40 kHz. IR detector**
❑ Thin gauge solid wire
❑ AWG 22 gauge stranded wire
❑ 2x3 pin header
❑ Thin heat shrink
*Use the pattern included in the download for this article to make
your PCB.
**I’m currently using an Electronics Goldmine G14560, but there
are plenty of other types available. Just watch their pin-outs.
If you’re interested in any of the sensors talked about
here, let me know. Right now, the line follower kit is
available on the Nearsys.com website for $9 plus $4
shipping. If there’s enough interest, I’ll create kits for
the other sensors. If you know a group that’s interested
in starting a robotics project but is concerned about
the price, have them check out the NearSys website.
