Plantenna: the plant antenna

The back story behind [Mike] experimenting with plants as AM radio transmission antennas antennae is rather interesting and worth the short read. But for those who just want the facts, [Mike] took an ATMega324, modified the PWM output into a sinusoidal AM signal (using a simple form of RLC circuitry), and connected the circuit to a plant no plants were harmed in the making of this project. The results? Well we’re not ones who would spoil the surprise, you’ll have to see for yourself in the video after the jump.

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Building a crystal oven

Radio communications depend on stable oscillator frequencies and with that in mind, [Scott Harden] built a module to regulate temperature of a crystal oscillator. The process is outlined in the video after the break but it goes something like this: A small square of double-sided copper-clad board is used as a base. The body of the crystal oscillator is mounted on one side of this base. On the other side there is a mosfet and a thermister. The resistance of the thermister turns the mosfet on and off in an attempt to maintain a steady temperature.

This is the first iteration of [Scott’s] crystal oven. It’s being designed for use outdoors, as his indoor setup uses a styrofoam box to insulate the oscillator from ambient temperatures. He’s already working on a second version, and mentioned the incorporation of a Wheatstone bridge but we’ll have to wait to get more details.

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Three pendulum harmonograph

Just the other day we were thinking “You know what we need more of around here? Harmonographs!” And our requests were answered when [Paul] sent in his three pendulum harmonograph. For those unaware, it’s a mechanical device that draws Lissajous curves or “really cool circles” to quote some of our staff.

[Paul] includes all the plans necessary to make your own harmonograph and begin drawing today. If you can’t wait, there’s a video of the three pendulum harmonograph etching a masterpiece after the jump. Continue reading “Three pendulum harmonograph”

Using A/C frequency as a clock signal

A while back we saw a logic clock that used the alternating current frequency from the power grid to keep time. We asked for information on your projects that use this method and we got a lot of comments and tips. Today we’re sharing [Doug Jackson’s] method which he used in his word clock.

The schematic above is from that project and we’ve outlined the important part in green. [Doug] pulls a signal from the 9V AC power before it hits the bridge rectifier, using a 100K resistor and a zener diode to protect the microcontroller pin. The code for that project comes as a hex file but he sent us the C code pertaining to this timing circuit. It’s written for PIC but you’ll have no trouble adapting it to other microcontroller families. Take a look after the break.

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Logic clock without an on-board oscillator

[Lucassiglo21] developed this logic clock without using a crystal oscillator or a resonator. Instead, he’s letting the incoming electricity keep the time for him. The supply is AC at 50 Hz so he’s using some 4017 decade dividers to reduce that down to a 1 Hz signal. From there it keeps track of the ticks just like the last digital logic clock we saw.

If you’ve used AC line frequency as the clock source in your project we’d like to hear about it. Send us a tip and make sure your writeup includes a schematic. We’re especially interested to see if anyone has a good way of using this method with inexpensive microcontrollers.

Modifying R/C frequency


Cheap radio controlled toys can provide countless hours of amusement, especially when friends have one too. You can’t always plan ahead enough for everyone to have a different frequency and sometimes, it just isn’t an option anyway. There is a solution, and it isn’t very difficult. [frickelkram] takes us through the process of changing the frequency that the toy runs on. He starts with the simplest way, which involves replacing one piece in the controller and simply adjusting the receiver. He notes that this often fails as the receiver just isn’t built to be adjusted easily. He continues to show how to get it done even if the first method fails.