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Simple wireless 1/0 transmitter/receiver 1

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Skogsgurra

Skogsgurra

Electrical
Mar 31, 2003
11,815
Need a simple device that can feel a contact closure and transmit the 1/0 state over around 100 m distance. More is better.

It shall be used for temporary check out of measurements and there is a demand for low latency, or at least consistent latency. Either less than around 500 us latency or same spread. In the latter case, latency could be up to 5 ms.

Battery supply. Not critical in any way. Could even use a small lead ackumulator. Operation for a week or so may be needed, but seldom more than five or six hours.

Looked at standard solutions from automation companys. But they all seem to have more latency or spread than I think will work.

Anyone?



Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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I would suggest Harmony XB5R controls, but I'm sure the latency isn't what you are wanting.

 
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Fiber optic link with a LED as Xmit and a photodiode as Rx? (still 'wireless')

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 
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All good suggestions. But not what I can use. Latency is important. Vary, And also need to move without being restricted by a "glass wire". The search continues. There's a BLE module. So I guess I should have a closer look at that. But, as far as I have understood, it won't be fast or deterministic enough.

Perhaps an IR transmitter with heavy "overdrive" will work best. Simple frequency stable chopping and a tuned receiver (need six channels) may be the solution. It works only for around 10 ms at a 1 or 2 % Duty Cycle. So it may survive the thermal abuse. Anyone tried that? There may be a problem with people walking in-between transmitter and receiver. Maybe "wall scattering" will work?

But, as said, a plug-and-go solution would be nice to find.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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Without a custom protocol, I doubt you're going to get the fixed, minimal latency you desire... most existing protocols bundle data into variable-sized packets, have variable transmit times, etc.

May make sense to make a junky burst transmitter that simply transmits 1W of a carrier frequency the instant a switch is hit. A similar receiver would be tuned to that frequency. Latency would be the few microseconds to enable the amplifier on the transmitter end when the switch is hit and move that signal through the ether 100m.

Dan - Owner
Footwell%20Animation%20Tiny.gif
 
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Unless you are certain it won't work, I think I would be compelled to try the Schneider Harmony XB5R as identified earlier by LionelHutz. It's readily available, relatively inexpensive and if you find it won't work, then you can look for another solution without having made a large investment in time and money.

Brad Waybright

It's all okay as long as it's okay.
 
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Yes, I sure need predictable tining here. And 500 us or better is what we need to get enough precision. I designed IR transmitters to keep track of busses and other vehicles so long time ago that I forgot about it. We were using remote (for TV) coding and around double the frequency of an ordinary remote. I could easily do that again. But without the phase coding and just send a powerful burst of IR square pulses. And then use AM MF filters to get the selectivity needed. That will give me fast reaction and long battery life. The links are temporary and I can probably use a lens to collimate light onto the receiver chip. That, plus a lot more power than we used then will hopefully bridge the 100+ m we need. If people get in the way sporadically, we can use historical data to fill in the missing one. Up to a limit.

I'll try that and I don't think that FCC or any other cop organization will object. Thanks for reminding me.

Sometimes, EngTips is like having a huge office "landscape" to put questions in. And get suggestions back from.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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Serendipity!

A word that was used ad nauseam some twenty years ago. But sprang to mind when I was looking for something entirely different and someone (must have been the google alf) said that I might be interested in this:

OK, I was. Very. But there is one little problem, does KB / S stand for kilobits? or kilobytes? In the latter case, my search is over. That would indicate a transfer rate close to 30 kb/s and that is way below my 500 us.

But, with 30 us/bit I can code each channel so I don't get the readings mixed up. Could be done even if it means kb. But then I have to wait a while for the decoding to say "OK - this for you". Any thoughts?

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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This other website says 4000 bits/s:
as does this: This latter site also shows a purported schematic of the transmitter and receiver.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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Thanks! So, they are slower than I hoped for.

But, the battle can stil be won, I think,

If the decoding takes a fixed time and is not influenced by length of actual telegram. PPM will do that. Then I qualify the code and when the last bit arrives, I output a True/False that can be used for the speed measurement. Then it doesn't matter if the qualifying pulse is there 2 ms after the pick-up senses the flag. As long as the time difference is constant, the result should be OK. The only cases where the delay is a problem will then be in very rare cases where position down to one or two degrees matters. But that is very rare and can, if needed, be solved by using plain copper wire.

Thanks again.


Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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Gunnar, Is it possible to process the signal at the source and then transmit the result, slower?

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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Like the confusion with M and m, Keith.

Bill, it could be done. Yes, but then I need to rethink the whole thing. And it is difficult for an old dog to learn new tricks. So I will do the PPM/constant latency thing. I see that it works quite well. Also found a way round the phase difference thing - thanks to constant latency. It is not the problem I thought it would be. Time is uniform in different places. At least in this case.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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Like the confusion with M and m, Keith.

Bill, it could be done. Yes, but then I need to rethink the whole thing. And it is difficult for an old dog to learn new tricks. So I will do the PPM/constant latency thing. I see that it works quite well. Also found a way round the phase difference thing - thanks to constant latency. It is not the problem I thought it would be. Time is uniform in different places. At least in this case.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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I just said that again, Keith!
There was a problem posting the first comment. And now - its twin appeared...

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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Update

I got a bag of those Tx and Rx modules. Dirt cheap. Well functioning. But, the hitch: There are lots of 433 MHz signals in the air from WiFi, local mouse and even the car keys. So I am testing with different "diversities". Space diversity seems to be a way, at least in this application. In the factories, there are more and more IoT devices and I think that a successful office test will not be equally successful IRL.

BTW, the speed is OK. So, my first worries are the least ones now. As the saying goes "You can turn as much as you can - but your ass will still be behind.."

And now, the customer starts tapping the table. Impatiently. May have to stick to copper this time.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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