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IR Servo Motor Interface for RCX

LEGO RCX-compatible infrared remote control for servos

IR Servo Motor Interface for RCX
One of the few features lacking from the LEGO Mindstorms system is an accurate positional drive. This has prompted the author to develop this interface circuit, which can control up to three servos of the type used in radio-controlled models via the IR-interface of the RCX brick.The three different types of LEGO Technic 9 V motors are more than adequate for most robotics projects. However, when accurate angular positioning is required, one can quickly become frustrated by the amount of play in the gears and start looking for a better solution. The servos used in radio-controlled models offer more precision. Of course, we will not only have to deal with mechanical interface problems of joining to other LEGO bricks: we will also have to operate under control of the RCX, which is a little trickier. The RCX brick is the main control element in the LEGO Mindstorms system. It consists of a microcontroller built into a large, bright yellow, LEGO brick.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1,R2 = 10kOhm
R3 = 330Ohm
R4,R5,R6 = 560Ohm
C1,C2,C4,C5,C11,C12 = 100nF
C3 = 4µF7 16V radial
C6 = 470µF 16V radial
C7-C10 = 22pF
C13 = 100µF 16V radial
D1,D2 = 1N4148
IC1 = 78L05
IC2,IC3 = PIC16F628, programmed, order codes 020356-41 (IC2), 020356-42 (IC3)
IC4 = 7805
IC5 = TSOP1738 (see text)
K1 = 9-V battery (see text)
K2,K3,K4 = 3-way pinheader
X1 = 18.432MHz quarts crystal
X2 = 14.3MHz quartz crystal (see text)
PCB, order code 020356-1
Disk, order code 020356-11 or Free Download
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