Traditionally, in a crystal detector radio tuned circuits, a mechanical type variable capacitor is used. For those of you who would like to eliminate this mechanical component, here is a modern version of the classic detector set. This radio, as shown on Figure 1, uses a varactor diode instead of the usual mechanical rotary device. [via]
Crystal Detector Radio Receiver Set – [Link]
Kerry Wong needed some ultrasonic range finders for a project so he build his own. He writes:
The theory behind ultrasonic ranging is quite simple. Typically a short ultrasonic burst is transmitted from the transmitter. When there is an object in the path of the ultrasonic pulse, some portion of the transmitted ultrasonic wave is reflected and the ultrasonic receiver can detect such echo.
He provides schematic and code on the link below.
A Sensitive DIY Ultrasonic Range Sensor – [Link]
This software radio made by PA3FWM is capable of capturing nine amateur radio bands (VLF, LF, MF, 160m, 80m, 40m, 30m, 20m, 15m) simultaneously. The radio receiver is controlled by a nice web interface that let’s you control which band you would like to listen. Check it out on the link below. [via]
9 band amateur software radio – [Link]
Emilio Ficara writes:
I have done a simple infrared remote control receiver with RS232 ascii output. It can be used for developing remote controls on a PC using the serial port. In practice, the infrared bursts are converted in ascii characters and sent to the RS232 port. The downloadable ZIP file contains the schematic diagram, the printed circuit board, the components disposition and the object file to write into the ATMEL ATtiny2313 microcontroller.
General purpose infrared remote control receiver with RS232 output – [Link]
USB Ultra Infrared Receiver to remote control and power on/off the PC. The extended guide for the infrared receiver with hardware side function to remotely switch the PC on and off as full USB variant is now available and got the name “USB Ultra infrared receiver” or briefly “USB Ultra IR”.
USB Ultra infrared receiver – [Link]
Now that we listen to MP3s, and watch XVIDs or x264s, a computer is the entertainment center in at least one room of most homes. Unless you have a special HTPC, though, you’re probably stuck using the keyboard to pause, change the volume, and fast-forward through annoying Mythbusters recaps. PC remote control receivers range from ancient serial port designs (who has one?) to USB devices not supported by popular software. In this how-to we design a USB infrared receiver that imitates a common protocol supported by software for Windows, Linux, and Mac. We’ve got a full guide to the protocol plus schematics and a parts list. [via]
Make a USB remote control receiver – [Link]
This is the Airband Receiver Schematic. It is basically an tweaked version of Richard Anderson’s Superregen Receiver (thanks for all the tips and comments, Richard!).
See the remarks below the hand drawing. The circuit is broadband by its nature, but if tuned well enough to the ACARS frequency (131.725) it will allow decoding of the messages even if the voice transmissions will be heard in the background.
Original Circuit: http://www.tricountyi.net/~randerse/superrgn.htm
VHF Airband Receiver – [Link]
This circuitry allows you to control your computer with a simple remote, like the one you already use for your TV-set. It’s very useful when you want to control a DVD or an mp3 player without having to stay at the keyboard. Please note that this circuit is NOT IrDA compatible and it won’t help you to connect to your mobile phone or whatever IrDA device; it’s only good to control your pc with a standard remote control. I use it for VDR and now my pc is a full featured set top box connected to the television, capable to digitally record and replay satellite television, DVDs and every kind of digital content (mp3, divx). There are many softwares you can install to control this ciruit; for Linux you can use Lirc and for Windows you can use either Winlirc, Girder, IR Assistant or uIRC.
How to build a simple but cool IR receiver – [Link]
Simerec’s SIS-2 programmable infrared receiver chip seems a quick solution for adding IR control to electronics projects – [via]
The SIS-2 monitors an IR receiver, and when a certain remote code is detected, an output pin will toggle. Two outputs are available and any code on any remote can be taught to the SIS-2. This makes it simple to implement an infrared (IR) remote controllable switching solution for a wide variety of applications. When used with an inexpensive IR receiver module, the SIS-2 recognizes IR signals from 2 independent IR remote control sources, and provides 2 modes of switching for your application.
Programmable IR Receiver – [Link]
Joe writes:This project is a great way for beginning builders to hone their skills at circuit construction. The receiver plans were originally printed in a September 2000 article in QST. I built mine from scratch, not on a printed circuit board, with no ill effects due to strange parts placement. The author provides very good advice about the audio/volume and regeneration controls placement and hookup (by being careful, no shielded audio cables are necessary). [via]
Shortwave Regenerative Receiver – [Link]