How to approach this project? (remotely controlled LED)  - Page 1
Forum section: electronics / beginners

author: Abstr7ct
author_rank: Regular Contributor
timestamp: July 17, 2013, 06:16:42 pm
content: Hi, everyone.I am an EE student and I'm still a beginner hobbyist in electronics; I don't have much experience in working with different components and ICs. The most ambitious project that I worked on was a basic arithmetic calculator based on a PIC microcontroller and a 16×2 LCD display screen. The program was over 200 lines and it was written using MikroC IDE. I know about transistors and op-amps and have used them in simple applications like switching and analog signal comparison, respectively.This time, I would like to build another simple project in a short time. The idea is to have a remote control with one button that switches on/off a tricolor LED from a distance of 2 meters at least. Any ideas or sources that can teach how to approach this problem? I would like you have your thoughts rather than jumping quickly to a search engine for help.Thanks.

author: Bloch
author_rank: Unknown
timestamp: July 17, 2013, 07:24:51 pm
content: Quote from: Abstr7ct on July 17, 2013, 06:16:42 pmWireless ?http://dk.farnell.com/infrared-emittersandhttp://dk.farnell.com/infrared-receivers

author: ben_r_
author_rank: Frequent Contributor
timestamp: July 17, 2013, 10:30:19 pm
content: Whats the application?You know you can buy something like this already made for dirt cheap now right?LINK

author: Paul Price
author_rank: Super Contributor
timestamp: July 18, 2013, 01:59:08 am
content: Interesting...but so many ways to do this!You could just use any remote control for a TV, DVD player, VCR etc. When you press any button, a serial bit-stream of infrared pulses is emitted. An infrared receiver (just three wires to hook up) will then give you a repeating digital code stream output whenever you push a button on the remote.Now, you are faced with a lotta options.The dirtiest way is to pull the infrared LED diode out of a discarded remote control to become an emitter, a source of invisible magic infrared light that only requires a 9-v battery to a button momentary contact switch and a current limiting resistor, approx. 50-ohms to the anode of the infrared diode , cathode of the diode returns to the neg term of the battery. Now you have the transmitter built.For a receiver, you can buy an infrared phototransistor/photodiode or else you can again take one out of a discarded DVD player VCR. etc VCR's use two of them standing up next to where the VCR Cassette sits to detect when the tape has run out in either direction and there is also one in the front panel inside a small remote control receiver, easy to spot because of its lens peering out of a small metal case.Now you hook the collector of the photo transistor/diode to +9V on the receiver, the emitter goes to the base of an amplifying transistor, emitter of the amplifying NPN transistor to ground through a 1K resistor. The collector of the amplifying NPN transistor connects to the cathode lead of the LED you want to light. The anode of the LED to +9V.Now you cover the infrared phototransistor/photodiode receiver with the same visually opaque very dark infrared passing piece of very dark red plastic that you've taken off the discarded remote remote control to shield your receiver from room light and sunlight or else your receiver LED will be on all the time.Now you just point your transmitter at the receiver and push the button!A more difficult and challenging way to solve this problem and spending a few weeks to do it, is to take an infrared receiver out of a discarded remote controller device and feed the output of it at the emitting infrared LED's pin to your scope and record the waveform for any particular button pressed on the remote control of interest. Be careful, the transmitted code is modulating a 38KHz carrier to eliminate room light interference and narrow the bandwidth of the transmitted signal in this common remote xmit-receive scheme.Another way to do this so that it only works with your custom secret remote control code is to modulate on and off the transmitting infrared diode with the output of a 555 timer at some fixed carrier frequency, say 38kHz. Then you can use an infrared remote receiver module to receive this secret code and feed it to MCU which can quickly determine the frequency and it then lights your LED. You then also simply press the remote button at a rapid pace to create low freq. code.

author: Psi
author_rank: Super Contributor
timestamp: July 18, 2013, 02:26:54 am
content: Yeah, infrared is the easiest to do.Get yourself a IR sensor module (they have 3 pins (GND,+5V and output) and will remove the 39khz IR carrier frequency themselves and output a digital signal.For the remote side of things you setup a mcu timer to generate 39khz and connect / disconnect in software that clk to an output pin that has the IR led + resistor on it.Google IR codes and waveforms for info on protocols you could use.

author: hlavac
author_rank: Frequent Contributor
timestamp: July 18, 2013, 04:05:08 pm
content: +1 for infrared. The usual scheme is sending a serial digital pattern modulated with low duty cycle carrier at 36-38kHz. It makes it easier to pick the signal up in the noise and wildly fluctuating IR light ambient levels.Find a nice IR receiver module like TSOP4836 and IR LED of matching wavelength.

author: MasterOfNone
author_rank: Regular Contributor
timestamp: July 18, 2013, 09:58:15 pm
content: I vote that a Wired Remote would be the best solution. That’s right you just need a switch, some wire plus a box (and possibly some connectors). Just think about it, with a Wired remote you have no extra batteries to change. And if you feel the need for batteries then the remote could power the LED.Alternatively you already know how to program PIC’s, so you could just use two PICs and two MCP2122 to encode the decode the Infrared data.But if you decide go with Wired Remote idea remember to use connectors that will disconnect easily, because back in the 70s there were lots of accidents caused by people tripping over the remote wire for their TV‘s and VCR‘s.