# ultra cheap and directional receiver without uC??

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#### danjel

##### Member
I want to make a super cheap and simple device that would be:
-tiny/light
-battery powered (cr2303)
-can receive a simple wireless directed control to turn on/off
-no uC

The idea would be to have a crowd of people holding these cheap devices (or wearing them as buttons) and then you could aim the transmitter at general areas of people and their devices would light up.

So what kind of transmitter is directional but has a decent range (let's say 40m)?

For that transmission technology is there a super simple receiver you can build that simply reacts as a switch?

Any ideas??

#### Diver300

##### Well-Known Member
The no microcontroller requirement is just silly.

If you are going to make hundreds of these, there is a lot of work involved. Using a microcontroller is something you will have to find out how to do just once.

The microcontroller is needed to sort out the signal from all sorts of noise that might be present. It will only cost the same as the battery. The radio receiver will be a lot more money.

#### danjel

##### Member
The no microcontroller requirement is just silly.

If you are going to make hundreds of these, there is a lot of work involved. Using a microcontroller is something you will have to find out how to do just once.

The microcontroller is needed to sort out the signal from all sorts of noise that might be present. It will only cost the same as the battery. The radio receiver will be a lot more money.
I can program microcontrollers so that is not the issue. I was just curious if there was an ultra simple way of implementing this.

AS an example have you seen cellphone "charms" they are tiny battery powered things that you can dangle from your phone and they light up when there is an incoming call. I am not sure how they work but they are simple tuned circuits that react to the microwaves.
I just figured there is some sort of tuned circuit you could make....

#### Diver300

##### Well-Known Member
The cell phone lights rely on the large field right beside the phone. If you want something to work at a 40 m or so, you have to either detect quite a small signal, so down near the noise level, or fry the front row of your audience.

#### blueroomelectronics

##### Well-Known Member
What do you consider "super cheap" how many are you planning to build?

#### MikeMl

##### Well-Known Member
The only way this will work is if you use light/infrared. That is the only way you can get a "radio beam" where the angle subtended by the beam is narrow enough to select one person standing next (3' apart?) to another at a distance of ~40'. Do the Trig.

You would have to use uWaves and a Parabolic Dish antenna about 6' across to do this using radio waves.

#### marcbarker

##### New Member
The only way this will work is if you use light/infrared. That is the only way you can get a "radio beam" where the angle subtended by the beam is narrow enough to select one person standing next (3' apart?) to another at a distance of ~40'. Do the Trig.
I think there's lots of different ways to transport the radiative illumination to the targets:

Best I can think of is CW Tone-Modulated IR laser + diverger optics + parabolic reflector. The IR energy concentration uW / cm2 made low enough not to be a risk to eyesight (even looking straight into the dish), yet high enough to activate a tuned super-regenerative reciever in each RX. The attenuation of the broad area beam over distance is minimal if collimated to the same size of the dish.

If you convert a standard car reflector lamp may be a cheaper possible. Perhaps use a defocused laser, or wide angle NIR LED.

Maybe a modified battery torch can be adapted to provide most of optics.

Or cheap dirty way could be an xy array of narrow-angle NIR LED's, driven by CW tone-modulation.

Reciever: The battery-powered Detector can contain a photodiode, a tuned circuit and 2-transistor regenerative amplifier feeding the LED directly (operating in class-c mode when energised )

Probably a fet, a bjt, 4 resistors, 3 caps, inductor, and a photodiode. Oh and an LED and battery

Anyone wanting to patent this, please remember: you saw this here first!

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#### KamalS

##### New Member
1. Laser (IR really won't work over long distances, > 6m)
2. Use the FM Tx I have been talking about and use a holtek encoder decoder with each unit having a hardcoded ID.

#### marcbarker

##### New Member
1. Laser (IR really won't work over long distances, > 6m)
2. Use the FM Tx I have been talking about and use a holtek encoder decoder with each unit having a hardcoded ID.

my 0.02: 1. IR seems to work OK over 93 million miles!

I'm puzzled now... I thought the OP requirement was that any RX would respond to the same signal? (no addressing at all)

edit: [joke mode=on] how about doing away with the battery+circuit in the RX, and just having a Neon instead? Use a Magnetron and power the neons passively!

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#### KamalS

##### New Member
marc, his point is that he wants to directional and cheap.

IR is not very directional and modulated IR spreads a lot.

Over short distances, in the scenario he mentions, laser would be nice.

IR would require encoding to work reliably and that would require expensive parts/uC that he does not want to use.

Remains a FM transmitter that cost a few cents.

#### danjel

##### Member
As quantity: 100-1000 of them. The total will depend on the price (even though I realise that the the price is also dependent on the total).

Target would be $5-10 per unit. And the lower the better. Even better would be <$5

This would be worn by a crowd of people so individually adressing them is not a good idea since they will be randomly distributed.

As for aiming, I don't need to aim at individual, just groups. i.e. I would like to have say 1/3 of a room light up while the other 2/3 doesn't respond.

I was also thinking about some sort of FM transmitter... how do I make the transmission more focused? How do I build a receiver?

#### MikeMl

##### Well-Known Member
... how do I make the transmission more focused? How do I build a receiver?
You have to use very short wavelengths, probably in the GHz. You need an directional antenna array which has an effective beam width of a few degrees, which requires an antenna with an aperture of several wavelengths, which if the antenna array apperture is 1-2 meters requires a wavelength of a fraction of a meter.

Unfortunately, the higher the freq, the tougher it is to make the receiver cheap.

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#### marcbarker

##### New Member
marc, his point is that he wants to directional and cheap.
I thought LED light travelled in straight lines

IR is not very directional and modulated IR spreads a lot.
What's IR photography from spy satellites? If the IR 'spread' and wasn't directional, wouldn't all the pictures the satellite took be too blurred?

And why would 'modulated IR' spread any more than unmodulated?

IR would require encoding to work reliably and that would require expensive parts/uC
Wouldn't radio also have the same signal issues as IR? I believe in the Military that IR is preferred over radio for reliable data links. Maybe someone can confirm?

Remains a FM transmitter that cost a few cents.
8 degree lens NIR LEDs are cheaper?

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#### KamalS

##### New Member
marc, I do not have hard facts or professional experience to back my points.

I do have experince though of trying to send data in various ways using "over the counter" components - IR, Ultrasonic, RF all fall in the same category of "non directional" for me .. yes the first two can be made directional provided you do not use modulated signals.

In case of modulated signals the signals have so much high selectivity (reciever side) that they bounce of walls and objects.. definitely people.

The OP does not seem to realize he still needs an addressable system - be it a sinlge person or a group of people - you still need addressing - UNLESS you don't have problems making the whole thing public (anyone can listen/join/or be interfered)

I am sure in the end, the OP would build the circuit I posted or audioguru's original diagram.

#### KamalS

##### New Member
I am still curious about the question marc posted!

I guess the army uses high resolution IR cameras instead of "over the counter" photodiodes? I am guessing here and would like some good answers

#### Nigel Goodwin

##### Super Moderator
I am still curious about the question marc posted!

I guess the army uses high resolution IR cameras instead of "over the counter" photodiodes? I am guessing here and would like some good answers
What's to know?, a camera uses a lens and focuses a specific area (depending on the lens) on to the target (film or whatever).

IR works in the same basic way as visible light - if you use a lens to focus the output from an IR LED you could produce a fairly narrow beam.

#### marcbarker

##### New Member
In the 1940's, somewhat before uCs were invented, there was a espionage listening device which was remotely 'addressable': http://en.wikipedia.org/wiki/Thing_(listening_device)

I say 'addressable' because of the lack of suitable electronic equipment around operating on the particular wavelength meant it was exclusive enough, and about as addressable as a 1980's cordless telephone using 'holtek' style coding. (Can record the tone burst modulation with a scanning reciever and re-transmit = 'replay-attack') .

I'm sorry I didn't understand the point about "selectivity & bouncing off walls". I suppose if modulated signals do scatter any more than unmodulated signals, then an unmodulated signal would be better?

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