motor, and digital pins 6 and 10 (chip pins 12 and
16) control the right. Probe the pins one at a time,
checking for a good 0V–5V PWM signal. Or use
LEDs for a quick visual test; place them short leg to
ground, long leg to the Arduino output pin, and look
for the control stick to work like a dimmer.
clean it with acetone and paper towels several times.
Place the print facedown on the copper-clad
board and place the iron on top. Apply pressure and
heat for about 3 minutes, moving every 30 seconds.
Let the board sit for a few minutes, then soak it in
a bowl of warm, soapy water for 30 minutes. After
soaking, rub the paper off with your thumb until only
black toner traces remain.
Mix an etchant solution with 2 parts hydrogen
peroxide to 1 part muriatic acid. Pour the etchant
over the copper board in a glass dish and agitate it
for about 10 minutes with a plastic implement or air
pump. When the unmasked copper has all dissolved,
rinse off the board and remove the black toner with
more acetone and paper towels (Figure E).
3. Build the H-bridge (optional).
You can buy an H-bridge motor controller like the
Sabertooth 2× 25 from Dimension Engineering, but
if you feel like an adventure, build your own. Here’s
how I built one on a custom PC board for about $35.
Download the circuit board layout and schematic
triple8.sch files from makezine.
com/22/rclawnmower. Also download Eagle from
cadsoft.de; the free version is fine.
triple8.brd in Eagle and use a laser printer
to print only the bottom layer on a piece of glossy
magazine paper. I have tried many types of paper,
and had the best results with my wife’s Cosmopolitan
magazines. Find pages with plain black text only, like
the backs of prescription drug ads, where they list
the side effects. Feed the page into the printer manually to make sure it goes in straight.
Turn your iron to its high setting. Scrub the PC
board’s copper side with a Scotch-Brite pad and
CAUTION: Always wear chemical gloves and safety
goggles while working with etchant, and take care not to
drip or splash.
Drill holes in the PCB at every hole location.
Solder the components on the board, following the
schematic. Start with the resistors and terminals,
and finish with the transistors and capacitors, making sure all the transistor gates point toward the
resistor networks that drive them (Figures F and G).
Finally, attach heat sinks to the 47A and 52A