Servo - July 2008

Loki Crosses the Pond — Part 2

noise. Install two or three 1N4001 diodes in series with the battery if you intend to use the 7.2V higher voltage battery pack. A bypass cap is sometimes needed on the servo battery line. Another possible addition is a seven-pin, double row, straight solder tail header for the optional LCD display (follow instructions in CA1). An external 16x2 LCD display could also be used. In this case, you might want to put the connector on the top of the PCB. Current software does not utilize the LCD display; and the RE0 and RE1 pins were usurped for use by the IR sensors. These PIC pins will need to be re-assigned if the LCD is used.

The above parts are all added to the prototype area of the QwikFlash board. Wire these per the “Servos and Sensors” diagram in Schematic 1.

There are hole positions for four miniature toggle switches on Loki’s body. I’m currently using only one for servo power. There is already a toggle switch on the QwikFlash board for 5V power, but it is wired after the 5V regulator chip. Builders might want to add a switch in the power line to the QwikFlash board, or for a board that does not have its own power switch.

Electrical

The electrical system on Loki is simple. It consists of a battery, switch, battery connector, and wiring. The free ends of this wiring are to be terminated in the power

Parts List

ITEM/DESCRIPTION QT Y QwikFlash board options

• Blank PC board only 1

• Parts kit for 452 demo board 1 -OR-

• Unassembled PC board and parts kit 1

• IC MCU Flash 32KX16 40 DIP 1

Available as programmed part from the author.

SUPPLIER/PN

Micro Designs Inc./QF-QFPCB3.1 Digi-Key/18F452-KIT-ND

Micro Designs Inc./QF-PARTS2 Digi-Key/PIC18F4620-I/P-ND (un-programmed)

Additional parts for prototype area of QwikFlash board

• Rectifier GPP 50V 1A DO- 41 3 Digi-Key/1N4001DICT

• Conn Header .100” SINGL STR 36 POS 1 Digi-Key/S1011-36-ND

• RES 2.7K ohm 1/4W 5% carbon film 2 Digi-Key/2.7KQBK-ND

• RES 1.0K ohm 1/4W 5% carbon film 4 Digi-Key/1.0KQBK-ND

• Qty. 10 5” jumpers and 20 headers 1 SchmartBoard/920-0006-01

• Qty. 10 7” jumpers and 20 headers 1 SchmartBoard/920-0007-01

• CST-100 six-position connector receptacle 1 Digi-Key/A19494-ND

• Crimp CST-100 pins 6 Digi-Key/A19520-ND

• Conn 2.1 mm female plug 5. 5 mm OUT 1 Digi-Key/CP3-1000-ND

Sensors

• Devantech SRF08 ultrasonic rangefinder 1

• Sharp GP2D12 IR sensor 2

Super Droid Robots/TS-012-008 Lynxmotion/SIR-01

Cables

I used four 4” pre-made “jumper” wires for the ultrasonic rangefinder (cut two blue 8” lengths in half) and six 6” yellow wires for the Bluetooth transceiver. These are available from SchmartBoard (the colors designate the length) and have female pins for .025” posts on either end. (These are great for working on proto boards.) The ultrasonic rangefinder cable will need a CST-100 six-position connector receptacle stuffed with six Crimp CST-100s. A tool is available to crimp the pins, or use a pair of needle-nose pliers to crimp the pin on the wire before inserting them into the connector receptacles. You’ll also want to solder in a five-position, single row, straight solder tail header into the backside of the ultrasonic rangefinder. One of the other standard length jumpers (red) would probably work for the SMiRF, but I wanted a connector body here. As an afterthought, I’d have put one on the ultrasonic sensor cable, as well.