short range (1~2meter) remote control
Device should be very cheap.
Pulsing infrared LED, as used in TV remote controls and similar.
anything else rather than IR? I want to send a password.
Only other thing is RF, or maybe acoustic (ultrasound).
But RF requires antennas and more circuit sophistication.
IR is pretty simple, and by far smallest for packaging.
You buy a chip pair, the transmit chip scans a keyboard and drives a LED flashing transistor.
The receiver chip hooks up to a spectrally matched photo diode or photo transistor, and maybe pulls down an output pin when a key is pressed.
Is simple.
And simple means cheeeeeeep
There were (or are) remote controls that operated on ultrasound. If you wish to communicate with a computer, consider using built-in audio jacks, mic, speakers, etc. You would need to experiment with codes for sending and receiving.
what I really want to do is, controlling a switch that is password protected. And I can control that from 1m~2m distance with a remote that is sending that password. No one else can operate that switch without me.
I once had a part time job with a company that built spa pumps.
Some of these pumps used a remote control which was via RF, and it used a secure rolling code similar to car entry systems.
All the remotes and receivers were identical, but only one remote would operate a specific receiver once it had been preset to the same point in the rolling sequence.
So we had literally hundreds of these spa pumps, but each only responded to its own particular remote transmitter.
Its a pretty secure system.
The remotes and receiver boards came in boxes of 100 from China. I don't know how much they cost, but probably not much. The transmitter fitted on a key ring and was quite small. The receiver board was about 20mm x 30mm.
The transmitter only had one button, which toggled a flip flop in the receiver on or off. Not too sophisticated, but good enough to control a garage door or turn a security light on and off.
Range was typically about 20 to 40 meters.
To synchronise a receiver to a transmitter, you hold a button down on the receiver board while pressing the transmit button. Any receiver will work with any transmitter once they are synchronised. But from then on they all work independently. Its good because if a receiver or transmitter stops working, you just replace it with another, no need to fix it.
Big distance transmitters are vulnerable to interception of signal. Somebody 40 meters away can record the password.
With such transmitters it is better to use two-way communication, for example remote control should generate password based on code sent by Door Lock TX antenna.
Distance can be reduced by using FSK distance measurement.
Modulated scatter can reduce cost of remote control: remote control made as passive device containing antenna attached to Schottky diode.When button is pressed, low frequency modulation signal is applied to diode.
Door lock T antenna transmits radio frequency, which is received by remote control antenna, modulated with Schottky diode and reflected back to door lock RX antenna. This way remote control can be made extremely cheap and simple.
But problem of password sniffing must be solved. Because with big antenna and good amplifier password transmission could be easily recorded and reproduced. I think readily available modules like "rs232 to wifi" or "bluetooth" or "nrf24l01p" etc. could be used. More attention must be paid to two-way communication protocol. For example, door opening will require different password each time.
Big distance is a problem. Password can be found any time. I want to make a transmitter that is fitted in my cloth or somewhere with me. Whenever I'm around the particular device, it will be turned on. and I leave that device, it turns off itself.
Here distance must not be over 2m. Because in that case some one standing beside can find my password. But inside the circle of dia 2m, it should work properly.
look at "medium range" rfid tech.
That should do what you want.
Problem is that a RF channel which works reliable over 1 to 2m can be intercepted over a much larger distance. Unidirectional "rolling code" encryption is a medium safe solution. An eavesdropping proof transmission needs a bidirectional channel to implement a challenge response scheme with strong encryption.
Its the very cheap part that is the stumbling block here.
All kinds of exotic protocols could be invented for security, even a spread spectrum system. But it will be neither simple or cheap.
this can easily be done with technology. An encrypted signal, spread either with digital coding or frequency hopped, can easily do what you want. The problem really is BATTERY LIFE. you want this thing to work when you are within a few feet, but be worn on your clothing and not need to be activated by the user. That means you would need to be transmitting a signal oftn to turn on the spa pump. That will eat up battery life.
If it were me, I would look instead at passive RFID technology, something that has a unique code paired with the one spa, and maybe 3 interrogators around the periphery of the spa, transmitting out all the time, and powering up the RFID chip which will then respond with the right code. Something at 880 or 915 MHz should work pretty well.
the rfid tag would be tiny.
IF you do not like the range you get, you could add a battery and use a powered RFID tag, which would easily work at the distance you want
Hi,
maybe like anti theft systems in a clothing store.
I think they work without battery.
But if it works for 1-2m, I don′t know.
Klaus