This document explains how to interface a variety of devices to the Red Dot Cricket:
Please note that the sensor wiring diagrams are specific to the Red and Blue Dot Cricket designs. The earlier Green Dot Crickets use a different wiring configuration.
First, proper connector wiring technique, applicable to all devices is explained. Then individual wiring diagrams for each of the devices are presented. Finally, supplier information is given.
Connectors are the bane of existence of all electronics. If there is one weak link in the reliable performance of any electronic system, it is its connectors. With this in mind, the importance of patiently and neatly built robot connectors cannot be overemphasized. Particularly since a robot is a mobile system subjected to various jolts and shocks, care taken in the construction of the robot's connectors will always pay off in the long run.
The Cricket uses 0.1 inch male header as its connector for both motors and sensors. These are not the easiest connectors to work with, but they have a very compact footprint.
The technique presented here has been time-tested to yield reliable results. There are four basic steps in the process:
The remainder of this section explains the technique, showing diagrams for building the standard DC motor connector.
It is important to use stranded, not solid, wire cable. Each length of stranded wire consists of a twisted bundle of very thin thread-like wires. Solid wire, on the other hand, is a single thick wire segment.
The advantage of stranded wire is that it is much more flexible than solid wire, and also less susceptible to breakage. One thread of a stranded wire lengths can break without affecting the performance of the connection, but if a solid wire breaks the connection is lost.
An ideal wire for building sensor and motor cables is 28 gauge ribbon cable. Ribbon cable is stranded; the 28 gauge is the right weight to carry the current required to drive motors while still providing excellent flexibility. Ribbon cable also ``zips'' easily, so that sets of two or three wires can easily be made. Finally, rainbow ribbon cable is brightly colored in a ten-color sequence, making it easy to keep track of which wire connects where.
The first step is to strip insulation from the wire cable and tin the wire ends. ``Tinning'' is the process of infusing the stranded wire end with solder.
Remove between 1/8 and 1/4 inch of insulation from the end of each wire. With your fingertips, individually twist the threads of each wire end tightly (follow the existing weave of the stranded wire bundle). Then, put a dab of solder onto the soldering iron, hold it to the wire end, and add some solder to the wire end. Draw the iron tip along the wire end to evenly distribute solder into the wire end.
In a similar fashion as the wire ends were tinned, put a drop of solder on each of the header connector ends to be soldered.
Cut a 1/4 inch length of heat shrink tubing for each connection, and feed a tubing segment onto each wire.
In preparation for soldering, align the wires with the male header pins as indicated in the diagram. If necessary, zip back the individual wires so that the tubing does not get in the way of the connection. (The use of a ``helping hands'' tool is helpful here---a tool with two alligator clips on flexible arms.)
Line up the wire ends with the male header pins and solder. Make sure that the heat shrink tubing is far enough away from the joint that the tubing does not shrink prematurely.
Slide the heat shrink tubing over the joints, and apply heat from a heat gun. If a heat gun is not available, the open flame from a match or butane lighter may be used. Hold the joint so the heat shrink tubing is at least 1 inch above the tip of the flame.
That's it! The connector end that plugs into the Cricket is now complete.
The DC motor connector uses two male pins on 0.2 inch spacing; i.e., the outer two of three pins. The center pin can be clipped away from the assembly, or, it may be pulled out of the connector body entirely using a long-nose pliers.
The Cricket uses a four-conductor connector for plugging in sensor devices. As indicated in the diagram, the connector is formed from 5--prong male header pins, with one pin clipped away to polarize the connector (i.e, prevent it from being plugged in improperly).
The pin labelled ``+5v supply'' may be used to power an active sensor. The pins labelled ``signal +'' and ``signal -'' are used to connect the sensor device. When the Cricket is reading the sensor value, +5v is present on the signal+ lead. The pin labelled ``ground'' is the system ground.
Resistive sensors, like the photocell, are wired across the "sensor+" and "sensor -" leads.
Switch-type sensors are connected to the Cricket's signal+ and signal- pins. Push-button switches are wired in the same fashion as the micro-switch pictured above. Please note that micro-switches should be wired to the "NO" (normally open) and "C" (common) pins. The 1K series resistor is used to protect the Cricket in case the switch is inadvertently plugged into a motor output.
The yellow LEGO touch sensor is wired to the same male header connector as the microswitch, but does not require the 1K series protection resistor. (The protection resistor is built into the LEGO switch itself.)
The infrared reflectance sensor consists of two discrete devices: an infrared LED emitter and an infrared phototransistor receiver. The receiver and emitter are matched, so that the peak sensitivity of the receiver is at the same wavelength of the emissions of the emitter.
The wiring for the reflectance sensor is straightforward. The emitter LED is powered by the Cricket's signal+ circuit, which supplies +5v when reading the sensor, with a 220 ohm resistor in series to limit the current through the LED to an appropriate value.
The temperature sensor uses a thermistor, a simple device whose resistance varies with temperature. We recommend the Digi-Key part number KC005T-ND which is compatible with the Cricket circuit.
Please make sure to use an ample length of the 1/16" heat shrink tubing at the connections on the thermistor. This is to protect the thermistor when it is immersed in water.
The Hall Effect Magnetic sensor detects the presence of a magnetic field. Small, permanent magnet sensors may readily be detected with this device. We recommend Digi-Key part number DN6848-ND for this application.
LEGO motor cables, motors, and touch switches can be ordered from LEGO Dacta. See their web page for contact info for your country.
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9983 |
standard 9v motor |
powerful; requires gear reduction |
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9849 |
9v micromotor |
little; weak; direct-drive |
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9887 |
motor connecting leads |
3 cables yields connectors for 6 motors |
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9888 |
touch sensor |
modify cable end as per diagram above; use discarded cable end as a motor cable! |
All of the other components (except the photocells) can be ordered from Digi-Key Electronics, phone (800) DIGI-KEY.
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R012-5-ND |
5 feet 9-conductor ribbon cable |
standard wire for building sensors |
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929400-01-36-ND |
male header pins |
36-pin strip for sensor/motor plug |
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CP332-5-ND |
3/32" diam, 5 ft length heat shrink tubing |
use at male header as an insulator and strain relief |
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CP116-5-ND |
1/16" diameter, 5 ft length heat shrink tubing |
use at thermistor to provide water-tight insulation |
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QRB1114QT-ND |
reflective photosensor |
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QRD1114QT-ND |
reflective photosensor |
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SW152-ND |
Omron lever switch |
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KC005T-ND |
thermistor |
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KC008N-ND |
high-sensitivity thermistor |
don't use hot glue on final assembly; leave part exposed |
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DN6848-ND |
hall-effect sensor |
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The photocell may be ordered from Mouser Electronics.
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338-54C79 |
PHOTO CELL PH CELL 100K TO 200K |
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