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[SOLVED] Transmitter for short distance (10cm)

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amirke

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Hello,

what would you recommend for a distance of 10cm more or less?
which transmitter system should I use?
I need to make a connection between 2 objects in this distance (very low rate data)
 

Hi,

What information did we get?
* 2 devices
* 10 cm
The rest is guessing.

What we don't know:
* why no copper cable? This should be the most obvious solution.
* what type if data? Digital, analog? What source? Temperature? pictures?
* what data rate? For one application "10Mbaud" is low, for the other application 9600 baud is high...
* moving objects or still objects? (If moving: how fast? Linear, rotating...)
* in free air? (It could be in water swimming, in space...)
* a barrier between the two objects? What material?
* optical / Ir, electromagnetic / RF, ultrasound..

Klaus
 

Hi Klaus

The info that you don't know:
No copper wire - that is a requirement
data type - discrete signal (button) with encapsulation - address, CRC etc..
data length - 10 bytes
data rate - can be very low. 9600bps is good as well.
still objects - both transmitter and receiver are in constant locations
In free air with no barrier in the middle
optical / Ir, electromagnetic / RF, ultrasound - everything is possible, but I need to get the smallest solution with the lowest power availble
 

Hi,

sounds like IrDa should be suitable.
Small, low power.
For 10 cm you even may reduce driving current.
You don´t need to include all the IrDa protocol stack. You may use raw data transfer also.

For one way communications there may be even smaller solutions.

Klaus
 
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    amirke

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OK, That is a good solution. with good power.

What other solution there is?
Maybe there will be an obstacle between the objects so I want to think on a second option
 

NFC/RFID ?
Can also supply power to a small microprocessor on the "slave" side, where the pushbuttons are.
 
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    amirke

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Just for fun I sometimes tune my waveform generator to frequencies that can be picked up on my AM radio nearby. The waveform generator is low power and has no antenna. Yet it broadcasts radio frequencies a distance of several inches.

I tune the units in the band above 560 kHz. I can tell when their frequencies match because I hear the radio make a humming sound at one spot, and next to it is a silent spot absent of static.

I think you could transmit data using a similar simple setup.
 

std_match said:
NFC/RFID ?
Click to expand...

RF solution sounds interesting.
regarding to sub1G frequency (which is where the RFID is)
wavelength is v/f (where v is phase speed/velocity of the wave and in free space, the phase speed is the speed of light)

So for 1 GHz => wavelength is approx 30cm

How does it affect a system where the distance between the transmitter and the receiver is 10cm?
 

Can anyone tell me what is the connection between wavelength and transmission distance?

for example transmission wavelength of 30cm for a distance of 10cm?
 

Hi,

I don't think there's a direct relationship.
But different frequencies may cause different damping and different reflections.

Electromagnetic waves behave similar to accoustic waves.
Audible tones have a wavelength of some centimeters to several meters. But you can hear them in 10cm proximity of the source and you can hear them hundreds meters away....if they are loud enough.

Electromagnetic examples:
An induction kitchen oven may work with frequencies causing several kilometers in wavelength...but it works with maybe a centimeter of distance.
Satellite may send the informations with wavelength of centimeters ... but you can receive them many kilometers away.

Klaus
 
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    amirke

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Thank you Klaus,

So you don't see any problem to transmit data modulated on ISM frequencies (with wavelength above 30cm) for low distances (below 10cm)?
 

Hi,

Again: I don´t think the wavelength is a problem.

Fou sure you need to ensure proper signal levels. (as with any other system, too.)

Klaus
 
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    amirke

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A simple solution would be and inductively coupled 13.56 MHz link. It can use simply send UART data with ASK.
 

FvM said:
A simple solution would be and inductively coupled 13.56 MHz link. It can use simply send UART data with ASK.
Click to expand...

Thanks FvM
Is there a reference to see for transmit data with inductive coupled?
 

Why not use Bluetooth Low Energy? There are cheap modules like the HM-10.
 

Is there a reference to see for transmit data with inductive coupled?
Click to expand...

Two ferrite inductors cores appart one of the other, not having a closed magnetic path, such as a bar or cylinder core, would make this job; even two inductors with air core would also solve, given the short distance; anyway there are better and cheap solutions as those spiral strips.
 
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    amirke

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