Creative Works of Tom McGuire

Infrared Transmit and Receive with a Logochip

2007/11/30 · No Comments

    When ever I find an easy way to do something I just have to make a record of it. There are some projects where you might want to do something wireless with the Logochip. This little circuit makes it pretty easy.

    First an explination of the Radioshack 276-640, the IR Receiver Module. It will receive signals from an IR(940nm) LED that is oscillating at 38killoherts. So if we want to send a series of 1′s and 0′s we modulate this 38KHz signal on and off.

    Fortunately the Logochip can produce the 38KHz signal and modulate it with very little effort from the software.  We’re going to set up the internal timer module to produce the signal and set up the serial UART to modulate it. So here let’s look at the schematic.

            LogoIRtranceiver

   This schematic shows the Logochip circuit to the left and the IR transmit and receive circuits to the right. There are two transistors involved in the in the transmit. The one that drives the LED is driven by the timer output PORTC bit 2 which is producing a 38KHz square wave. But most of the time it is being held off by the other transistor which is being driven by the transmit pin (TX) PORTC bit 6. Now when you tell the serial port to transmit an 8 bit byte the serial data comes out of the TX pin and modulates the 38KHz signal on and off to the LED.

   On the receiver side (this is really easy) the Radioshack part is simply hooked up to the 5 volt power and ground and the output signal runs right into the receiver input (RX) PORTC bit 7. I put a resistor to ground just in case the output drifts. That’s it.

    Here’s a picture of my bread board. IRlogoProtoBoard . The transmit LED and the receiver module are pointing straight up and I just help my hand above it to reflect the signal back. I can’t wait to use it in something.

    So here’s the Logochip code. I hope I commented it well enough for everyone to follow.

                      TextPage

Have fun…

Categories: Logochip



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