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Tex and Rex, The IR Twins
In the August 2010 installment of the Nuts and Volts PICAXE Primer, we constructed stripboard versions of Tex and Rex. The PC board versions that are discussed on this page are functionally the same as the stripboard versions; they are simply intended for experimenters who prefer to work with PC board circuits.
The following photos show (in order) a bare Rex board, an assembled Rex board, a bare Tex board, and an assembled Tex board. (You can click on any photo to view a larger image.)
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| Rex (Bare) | Rex (Assembled) | Tex (Bare) | Tex (Assembled) |
If you have read the PICAXE Primer article that originally presented Tex and Rex, you will notice that the pin-outs of the six-pin breadboard connectors differs from the stripboard version of each circuit. I took advantage of the flexibility of PC board layouts, and arranged the pin-outs in a more logical order, and also made them the same for both boards. As you can see in the photos, the function of each pin is labeled on the PC boards. The following table clarifies the one-character label that I chose for each function (reading from left to right):
Pin-out Specifications for Tex and Rex Breadboard Connectors
| Pin | Description |
| 1 | Ground |
| 2 | SerOut |
| 3 | I/O 1 |
| 4 | I/O 2 |
| 5 | SerIn |
| 6 | +5V |
Understanding Rex
The schematic for the Rex PC board is shown below. The PNA4602 output pin is directly connected to the 08M's input 3 because that's the only input capable of decoding the SIRC signals. If you are still using a serial programming connection, resistors R1 and R2 provide the basic PICAXE programming circuit. (If you are using a USB programming adapter, it will also function correctly with Rex.) I/O pins 1 and 2 are brought out to the 6-pin breadboard connector for use in your projects.
Understanding Tex
The schematic for the Tex PC board is shown below. If you are still using a serial programming connection, resistors R1 and R2 provide the basic PICAXE programming circuit. (If you are using a USB programming adapter, it will also function correctly with Rex.) Resistor R3 is the current-limiting resistor for the IR-LED. The value of 180 ohms that I used (see Tex's assembly instructions) results in a current-draw of approximately 22mA, which is slightly lower than the 08M's maximum output current of 25mA. If you prefer to conserve power (and to decrease Tex's range), you could increase R3 to 220 or 330 ohms.
Input 3 is connected to the IR output circuit. This prevents the input from "floating" without necessitating a fourth resistor in the circuit. Jumper J2 allows you to connect either output 0 or output 2 to the IR-LED. Output 0 should be used whenever you want to transmit SIRC codes; output 2 can be used to produce a 38 kHz PWM signal for any project that requires an IR beam for simple object detection circuits. Placing a 2-pin shorting jumper on the upper two pins of J2 connects output 2 to the IR-LED; placing the jumper on the lower two pins of J2 connects output 0 to the IR-LED.
I/O pins 1 and 2 are brought out to the 6-pin breadboard connector for use in your projects. However, if you use output 2 for the IR-LED, it won't be available as a general-purpose I/O pin via the breadboard connector. Finally, since I/O pin 4 is not connected to anything in Tex's circuitry, it's a good idea to configure this pin as an output in your software, so that it isn't a "floating: input.
Rex: A Flexible Learning Tool for Infrared Reception: $1.95 each (Bare Board)
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Tex: A Flexible Learning Tool for Infrared Transmission: $1.95 each (Bare Board)
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