A Dead Simple, Well Constructed FM Transmitter

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[Angelo] is only 15, but that doesn’t mean his fabrication skills are limited to Lego and K’Nex. He’s built himself an amazingly well constructed FM transmitter that’s powerful enough to be received a quarter mile away.

The FM transmitter circuit itself is based off one of [Art Swan]‘s builds, but instead of the solderless breadboard construction you would expect to find in a small demo circuit, [Angelo] went all the way, etching his own PCB and winding his own coil.

Using photosensitized copper clad board, [Angelo] laid out the circuit with Fritzing, etched a board, and went at it with a drill. The components found in the transmitter are pretty standard and with the exception of the trimmer cap and electret mic, can be picked up in the parts drawers of any Radio Shack. He gets bonus points for using a 1/4 – 20 bolt for winding the coil, too.

The power supply for the transmitter is a single 9V battery, the battery connector being salvaged from a dead 9V. Awesome work, and for someone so young, [Angelo] already seems to have a grasp of all the random, seemingly useless information that makes prototyping so much easier. Video below.

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Super Simple FM Transmitter

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Making your own FM radio is practically a rite of passage for hackers. How about making a small FM transmitter?

Originally designed by the Japanese multimedia artist [Tetsuo Kogawa], this simple FM transmitter can be built with only 10 components and about an hour of your time. The method shown here is one of the easiest to build, and it’s called the Manhattan Style — the same method used when [Bill Meara] built his BITX radio. It’s unique in that instead of using traces it uses one copper PCB which is used for all ground connections, and then small islands of the same PCB glued on top to form nodes for the circuit to connect to. Besides being an extremely easy way to make a PCB without any fancy tools, it also makes you think about circuits in a different light. In fact, it gives “floating ground” a whole new meaning!

While its 10 component count is impressive, it can’t beat this 3 component FM transmitter we shared a year ago! Stick around after the break to see how to make your very own.

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Hackaday Links: November 17, 2013

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If you purchased a knock-off FM transmitter and were unhappy with its broadcast range [Thiagohersan] shows how to double the range with a simple transistor amplifier circuit. He also hacked it for used without the 12V car socket.

[Patrick Herd] had a project that required him to strip about twenty Mindstorm batteries from their plastic enclosures. It’s not too tough getting into them but it does require drilling out the plastic rivets. He made a jig and used a CNC mill to automate the process.

Speaking of CNC, [Bertho] added some abstraction to distance himself from what he calls the “50+ years archaic syntax and grammar that G-code programs have”. The project is a meta-compiler for G-Code.

If you need a cold one and don’t have a HaDuino on hand you’ll thank yourself for hacking together this five-cent workbench bottle opener.

Just make sure you do all the lathe work for a custom speaker enclosure before you start pounding back those brewskis. Not only does [Shaun's] creation look modern and stylish, but it boasts more than enough power to bump some tunes.

Here’s a project that adds LED feedback to your XBMC installation. It uses a Raspberry Pi to run the media center software, and a script to monitor it and actuate the lights on an Adafruit add-on board. At first glance you may not think much of it, but this is all the logic control you need to automate your viewing room. Who doesn’t want a home theater that automatically dims once you’ve made your viewing selection?

And finally, [08milluz] snagged some reactive electronics in the form of Disney’s Mickey Mouse ears. Apparently they glow different colors at live shows and based on where they are worn within the park. He did a complete teardown to show off the hardware within. It turns out to be controlled by an MSP430 which are known for their low power consumption. [Thanks Spikeo55]

Transmit FM using Raspberry Pi and no additional hardware

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Now here’s a project that actually hacks the Rapsberry Pi rather than just using it as an embedded computer. [Londons Explorer] figured out how to turn the RPi into an FM transmitter. For now it’s done entirely in the user space, but we’re sure it could be improved if someone wanted to drill down further into the hardware. For those wanting to give it a try he’s rolled everything into a simple python package.

The technique requires nothing additional except a 20cm wire to serve as an antenna. The trick is to map GPIO pin number 4 to a position in memory. The clock generator is then used to toggle this pin at 100 MHz, which is the frequency to which your radio should be tuned. A fractional divider adjusts the frequency based on the sound file being transmitted.

The proof of concept for this was able to reliably transmit at a distance of about fifty meters through several walls. The problem is that this technique is limited in the amount of data which can be sent. Right now it’s only about 6-bit audio. But descending deeper through the abstraction layers to put DMA (Direct Memory Access) to use may be able to improve upon this.

[Thanks Owen via Reddit]

Re-engineering some FM transmitter firmware

[Furrteck] had a little adventure with this FM transmitter he picked up on eBay. It worked alright, but he wanted to be able to scan through the frequencies, and to have the device return to the same settings after power cycling. He cracked it open and got to work to achieve all of his goals.

The device is driven by an ATmega48, and there’s a 6-pin ISP header on the board. An initial read of the chip wouldn’t work, and he soon discovered the unstable power supply was to blame. After connecting his own regulated source he could read the chip id without a hitch, but the code is locked so no dumping was possible. Fortunately he managed to trace out the board, and includes a full schematic in his write up. With this in hand he erased the chip and started programming his own firmware from the ground up.

The video after the break shows off the completed project. He can now scan through frequencies with audio feedback to let he know when he’s found a station to hijack. The new code will also write a tuned station to EEPROM for use the next time the rig is powered up.

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[Sprite_tm]‘s three-component FM transmitter

When the Regency TR-1 transistor radio came out onto the market in the 1950s, it was hailed as a modern marvel of microelectronics. With only four transistors and a handful of other components, the TR-1 was a wonder of modern engineering. [Sprite_tm] may have those old-timers beat, though. He built an FM transmitter with the lowest parts count of any transmitter ever.

Like most of [Sprite_tm]‘s builds, it’s an unimaginably clever piece of work. [Sprite] overclocked the internal RC oscillator of an ATtiny45 to 24 MHz. After realizing the PLL running at four times the frequency of the oscillator was right in the middle of the FM band, he set about designing a tiny FM transmitter.

[Sprite_tm] remembered his work on MONOTONE and made a short song for hit ATtiny. The firmware for the build takes the notes from his song and varies the 96 MHz PLL frequency a tiny bit, thereby serving as a tiny FM transmitter.

Does it work? Well, if you want to compare it to a Mister Microphone, the range is incredibly limited. That being said it works. It’s an FM transmitter built out of a microcontroller and a battery, and that’s very impressive. Check out [Sprite_tm]‘s demo after the break.

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FM stereo transmitter

Reader [Mike Y] responded to our “What are you working on?” post  with his stereo FM transmitter project. If you’ve ever used an FM transmitter for your portable audio, you know that even the best consumer level ones can be difficult to make sound decent.

He obtained an NS73M FM Transmitter module from Niigata Seimitsu Company, but it required a controller to handle pre-emphasis, modulation level, frequency, and power level. He decided on an Arduino which would also control his LCD.

His results were quite good, with decent range and superb audio quality. His total cost thus far is $35, but he still needs to put it in an enclosure. You can find complete schematics as well as source code and helpful tips on his site.  You may also want to check out the regulations on broadcasting(pdf) as well.

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