Servo - March 2014

left and right leg continuous rotation servos are plugged into headers B. 5 and B. 4, respectively. Note that all header connectors get powered from switched battery voltage except B. 6, which gets 5.0 volts from the DC booster module mentioned below.

Board layout.

For object detection and measuring distance, a Sharp IR distance module is CAed on top of a standard nine gram servo on the front of the circuit board, so it can look around and sense objects. Position the servo horn so that the sensor points forward in the center of travel and the servo rotates about 90 degrees left and right. The Sharp module's analog output goes through a soldered-on servo-style cable routed around the servo for rotation, and connects to an ADC via the B. 6 header. The positioning servo plugs into the B. 7 header.

Input from nearly any 38 kHz IR receiver module (like a TSOP4838) is hardwired to input-only pin C. 6, and a mechanical 5V beeper connects to pin C. 7. Since the Sharp sensor and beeper require 5 VDC, it is convenient to run all the electronics at 5V. The $1 USB DC booster circuit available at www.ebay.com /itm/181289201783 generates five volts from the four volt Li-Ion battery.

Remove the USB connector to save space. All servos run directly off of the four volt battery. A three-position, center-off power switch selects between electronics only for programming (no servos), or electronics plus servos for normal operation.

The PICAXE requires two resistors (10K and 22K) for the download circuit (shown in the schematic) which need to be added to the board. A three-pin connector or stereo jack is also required, depending on your USB/serial connection. I used a PCB jack, which obviously must be mounted on one end of the board since the robot legs block access to the sides.

Assuming your newly-built circuit board passes the smoke test and you can program it with the PICAXE Editor through a USB/serial adapter, you'll need a universal remote set up as a Sony TV remote.

To test your remote, connect your computer and run this short routine:

#picaxe 20m2 remote: irin c.6,b7:sertxd(#b7,13,10):goto remote

You should see numbers in the terminal window (F8) when you press the remote keys.

Check out the photo that shows a top view of the board mounted on top of SpiderBot. Fabricate some styrene crossbars and glue them atop the left and right leg gearboxes to hold the circuit board and add some structural rigidity.