500 mesurement points wireless (discussion)

[joseLB]

Dear Friends

I wiil try to revive here old times of great discussions whe used to have at this forum.

What I have today (wired):
please, see attached image

At the image there are 500 measurement points conected thru wires (2 meters max) to 100 pics.
Just one pic is transmiting data to PC at same time

NEW APROACH: -> to eliminate the 500 red wires, substituting for wireless betwen the 500 points and their corresponding 50 pics.
Each 250 points/50 pics are inside a large metal box (2 containers), so, they are "inside" a faraday cage (good, but lots refletions too).

On the new approach, each measuring point could have a small pic and transmitter. Each point already has a battery cell with 2 volts, that could be "elevated" to 5 volts. Energy consumption is not a big problem.
Each measure point would have to transmit at minimum at 9.600 bauds (19.200 would be better), to cope with time. Also, when requested to transmit, a point must start asap it´s transmission (very low time to turn on/sync transmitter).

I thought about bluetooth. I´m brand new to bluetooth, so come to my mind if it´s possible to have 250 + 50 bluetooth transmitters/receivers. All them could have their transmission off, turning it on when requested by the corresponding PIC and sending their data. I heard that there is a 4ms on/sync time, that would be a warning issue, but maybe acceptable, that´s true? I guess that leaving 250 + 50 transmiters on, shoud create some noise or traffic jam... or not?

I thought about a 433MHz transmitters/receivers (those used in remote controls) , all them listening, and when a PIC address someone, it would turn on it´s transmitter and send the data. But I think that 433MHz could transmit just up to 1.200 baud (that´s true?) see this (up to 500kbps) http://www.micrel.com/_PDF/micrf218.pdf ---- http://www.ti.com/lit/ds/symlink/cc1101.pdf ---- http://www.semtech.com/wireless-rf/rf-t ... s/xe1203f/ .... (google search: 433 mhz data rate )

In the same line i thought 38KHz IR leds/receivers (used in TV remote control), but here 1.000 bauds is a problem as well as aligning them to it´s PIC receiver and vice-versa. This probably would not work.
I guess that leaving 250 + 50 transmiters on, shoud create some noise or traffic jam... or not?

I think that wifi or derivates (zigbee, myfi, etc.) shoud be very complex, will need large pics at the 500 points, stacks, and long turn-on and sync times.
So, anyone have another suggestion or a clue about above?

Thanks in advance
Jose Breitinger

[jpc]

Jose,

thanks for the challenge for a start, can you tell a litlle more about the requirements? What sort of data has to be sampled and at what frequency? Do you need a permanent stream of samples at a fixed rate or is this on request of the pc only ?

[joseLB]

Hi JPC

Are sampled 3 adc values (6 bytes to be transmited). The PC does a request for one PIC at a time that makes request to one of point pics at a time (5 requests). So each point pic sends the 6 bytes (total 6bytes x 5points = 30 bytes plus protocol). That´s the reason the transmitter turn on/sync shoud be short or, all transmiters must be turned on all the time.

But I think than to maintaintx on at 250 points + 50 pics, would be a problem in noise or trafic jam or even address in bluetooth or wifi (I know nothing about these protocols -> I only know that to connect wifi to my pc/smartphone, take many seconds, that is proibitive here). I have about 5-7 seconds do do a roundtrip on all 250 points. So, 9.600baud x10 bytes =~ 10 mS x 250= 2.5 So, protocol, on/sync, etc. could take another 10 ms for each point at most.

My preference would be to 433MHz or similar (like the manuals above), as they are simpler to implement (soft/hard, ex: no stacks, simple handshakes, etc.) and point pics could be small ones, like 16F with low pin count.

So, my question is about Transmission technologies (wifi, bluetooth, 433Mhz or similar or ? ....?)

Regards
Jose

[jpc]

you might have a look at NRF24L01+ modules, they provide quite reliable communication at low price, i used them recently with 16F1825 which has more than enough resources for your job

[joseLB]

you might have a look at NRF24L01+ modules, they provide quite reliable communication at low price, i used them recently with 16F1825 which has more than enough resources for your job

Thanks JPC,
I´m still Reading the datasheet, and I am really impressed.
Seems at this lecture point that it was done for my case, he,he...

And seems that it´s simple to control... at least at first glance.

Again, thanks
Jose