Emergency Egg Locator Beacon (EELB)

Description: This project was inspired by a circuit that a friend, Simon Field, showcased. He built a simple transmitter circuit using a 1 MHz "can" oscillator and a serial connector. In his circuit, he utilized a computer to turn the transmitter on and off and to send Morse code. In the United States and possibly elsewhere, there is a tradition at Easter to hide Easter eggs for children to search for. While some eggs may be real, most are plastic containers filled with candy. Children find the eggs, extract the candy, and often become hyperactive from the sugar. Occasionally, the Easter Bunny may forget where the eggs were hidden, leading to the creation of the "Emergency Egg Locator Beacon" (EELB). The EELB is compact enough to fit inside a plastic Easter egg, leaving space for candy. It emits a customizable message on the AM band, which can be received by any transistor AM radio. Using simple radio direction finding techniques, individuals can locate the missing eggs. The project utilizes the PIC 12F6xx series microprocessors, which feature a clock mode that outputs a divided system clock on one of the pins. The internal oscillator can run at 4 MHz, allowing the PIC to generate a 1 MHz output on CLKOUT (pin 3). This output drives a 220-ohm resistor connected to an LED, which is grounded by pin 2. A capacitor is connected to the LED's anode, and a length of wire is attached to the capacitor, enhancing the signal's range. The amplitude of a sine wave is modulated over time, and the AM radio receiver filters out the carrier frequency, leaving the desired signal. By configuring the oscillator mode to INTOSC_CLKOUT, the PIC generates a 1 MHz clock on pin 3, which is suitable for the carrier frequency. To modulate the 1 MHz carrier, pin 2 (GPIO 5) is toggled on and off. When pin 2 is on, the LED is reverse-biased and does not illuminate, causing the output of pin 3 and the LED's anode to oscillate between 0V and Vdd at 1 MHz. When pin 2 is switched off, the LED's cathode is grounded, and the voltage at the anode is approximately 2.1V for a red LED. This modulation allows the 1 MHz clock signal to vary between 5V and 2.1V. The software for this project is straightforward, utilizing the 12F6xx's 8-bit timer with a settable prescaler. The timer generates an interrupt upon overflow. The software initializes the timer with a prescaler of 8 and a preload value of 133, resulting in an interrupt approximately every millisecond. The interrupt service routine counts the interrupts, and after 100 interrupts (0.1 seconds), it sets a flag for the main program. Additionally, the routine toggles the state of pin 2 based on the logic level being sent. This toggling at a rate of 1 ms modulates the 1 MHz carrier wave with a 500 Hz signal.

The Emergency Egg Locator Beacon (EELB) circuit is designed to aid in locating hidden Easter eggs by transmitting a signal on the AM band. The circuit primarily consists of a PIC 12F6xx microcontroller, an LED, a resistor, and a capacitor. The microcontroller is configured to generate a 1 MHz output signal, which serves as the carrier frequency for the AM transmission. The modulation of this signal is achieved by toggling the GPIO pin connected to the LED, which alters the amplitude of the output wave.

The 220-ohm resistor limits the current through the LED while the capacitor connected to the anode of the LED helps in determining the effective range of the transmission. The length of the wire attached to the capacitor acts as an antenna, enhancing the signal's reach. The modulation of the carrier frequency is critical for the AM radio receiver to interpret the transmitted message accurately.

The software runs on the PIC microcontroller, utilizing an 8-bit timer to create timed interrupts. The timer's prescaler is set to 8, allowing it to generate an interrupt approximately every millisecond. This precision is crucial for maintaining the modulation frequency and ensuring the reliability of the transmitted signal. The overall design allows for a compact and efficient solution to the problem of locating hidden Easter eggs, demonstrating the effectiveness of integrating simple electronic components with traditional festive activities.This project was inspired by a circuit that a friend of mine, Simon Field, over at Scitoys. com showed me. He had built a very simple transmitter circuit out of a 1Mhz "can" oscillator and a serial connector (see it here ) In his circuit he used a computer to turn the transmitter on and off and to send Morse code. In the United States (and possibl y elsewhere) there is a custom at Easter to hide Easter eggs so that the children can search for them. While some of the eggs may in fact be the spawn of chickens, most of the time they are egg shaped plastic carriers into which candy is placed.

The kids find the eggs, they extract the candy, and then the kids run around at supersonic velocity on a sugar high all afternoon. Of course sometimes the Easter Bunny forgets where he hid the eggs. Technology to the rescue! This project is an "Emergency Egg Locator Beacon" or EELB for short. The EELB is so small it could easily be embedded in a plastic Easter egg with room left over for candy treats.

It emits a customizable message on the AM band that can be picked up by any transistor AM radio, and with simple radio direction finding (RDF) techniques anyone can locate the missing eggs. I was reading the datasheet for the PIC 12F6xx series of microprocessors and noticed that there was a clock mode that fed the system clock, divided by four, out one of the pins.

The presumed used is for external synchronization but I had other ideas. Further, the 12F6xx series PICs have an internal oscillator that can run them at 4Mhz. So here we had a computer in an 8 pin dip that could put 1Mhz out on one of its pins. I couldn`t pass that up. The PIC is configured to generate a 1Mhz output on CLKOUT. (pin 3 in the datasheet). That pin drives a 220 ohm resistor which is connected to an LED that is then "grounded" by pin 2. A capacitor is tied to the anode of the LED (more about that in a minute) and a length of wire is hung off the capacitor (the longer the better, up to 1000` :-) In the figure a sine wave`s amplitude is being modulated (changed) over time. If you were to filter out the base frequency you would be left with a simple rectangular waveform. This is exactly what an AM Radio Receiver does, it tunes a circuit to the carrier frequency, and then filters out the carrier leaving its change in amplitude as the signal you want.

By setting the oscillator mode to INTOSC_CLKOUT in the configuration register, our PIC generates a 1Mhz clock on pin 3 of the package. Since 1Mhz is smack dab in the middle of the AM band it works out nicely for our carrier frequency. To modulate the 1Mhz carrier the PIC is programmed to turn pin 2 (GPIO 5) on and off. When pin 2 is on, the LED is reverse biased and does not turn on. Consequently the output of pin 3 and the anode of the LED, goes from 0v to Vdd at a frequency of 1Mhz.

However, when pin 2 is switched off the cathode of the LED is grounded. Now the voltage at the anode is simply the forward voltage drop of the diode, or about 2. 1V for a red LED. In this way the amplitude of the 1Mhz clock out signal can be modulated between 5V and 2. 1V by changing the state of pin 2. The software for this project is also pretty straightforward. The 12F6xx has an 8 bit timer with a settable pre-scaler. The timer creates an interrupt whenever it overflows. The software initializes the timer with a prescaler of 8 and preloads it with a value of 133 so that it will interrupt approximately once every millisecond. During the interrupt service routine, the number of interrupts are counted and once 100 of them have been seen (or.

1 seconds), the interrupt routine sets a flag to tell the main program that. 1 seconds has gone by. The other thing the interrupt service routine does is to toggle the state of pin 2 depending on whether or not the PIC is sending a logic 1 or a logic 0. The toggling of pin 2 at a rate of 1mS causes the 1Mhz carrier wave to be modulated by a 500Hz squ