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Micro power transmitter for remote sensor help
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beananimal

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Joined: 09 Feb 2006
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PostPosted: Tue Apr 19, 2011 4:49 am    Post subject: Micro power transmitter for remote sensor help Reply with quote

Looking for advice:

Collection cup on a filter device. Looking to sense cup overflow and shut down pump. The collection cup is removed and cleaned several times a week, so wired sensors are kind of a pain. I would like a wireless solution with an extended battery life (months or years). When cup overflow is sensed, the pump will be shut down.

Cup overflow is catastrophic and can happen in seconds so the sensor can not be passive, it has to be active. My thought is that if the reciever loses track of the signal (dead battery, etc) then the pump will shut down. The level sensor (likely a reed based float switch) will interupt the wireless transmission, also shutting down the pump.

Notes:
AVR with receiver will be close by within a few feet.
AVR will control relay that powers 120V filter/pump.
Transmitter will be waterproofed and attached to collection cup.


Any idea for appropriate wireless products? Again, I don't need to send or recieve any data but would like a product that gives me an extremely long battery life and is not going to be interfered with by common household electronics (cell phones, wifi, cordless phones, etc.)

In other words, I have a 120V pump with a removable filter cup. The filter cup must not be allowed to overflow and needs to be monitored. Because the cup must be removed very often, I do not want to use a wired connection to the rest of the filter or avr controller. I want the cup to communicate with the controller wirelessly and continuously for many months without a battery change.

Thoughts?
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reinhars

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PostPosted: Tue Apr 19, 2011 5:45 am    Post subject: Reply with quote

Perhaps RFID could be your friend.
E.g. http://middlefirst.wordpress.com/2009/08/11/hackaday-post-3-attiny-rfid-tag/
Without wires how you like it - and of course without battery.
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beananimal

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PostPosted: Tue Apr 19, 2011 2:30 pm    Post subject: Reply with quote

I like the idea, but it is not going to be very practical for this application. The range is too small to be of use. Interesting link though Smile
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JC

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Location: Cleveland, OH

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PostPosted: Tue Apr 19, 2011 5:08 pm    Post subject: Reply with quote

What is the range?

How large, physically, can your battery be?

Is there 120 V to run a wall wart as the primary power supply, with battery back up, at the site of the cup?

Your concept of continuously transmitting from the sensor to the Main Unit conflicts with your long battery life goal, obviously.

Truely, for reliability, one would hard wire the sensor signal to the pump shut off, and eliminate any RF link...

If the range works, I would put a Bluetooth module at both ends.
I would have the sensor send an "OK" signal once every 250 mSec.
The Main Unit would shut the pump off it it goes > 800 mSec without a response, for example.

You could, if you wished, also have the sensor unit transmit its battery voltage to be displayed at the Main Unit, if desired.

JC
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beananimal

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PostPosted: Tue Apr 19, 2011 8:58 pm    Post subject: Reply with quote

The range is less than 10', could even be 1 or 2 feet.

The battery can be a few stacked coin cells. or few AA or AAA cells.

The reciever will be 120V powered and control the equipment power via a relay. I just need a way to sense a single high level event in the cup and transmit that event to the controller.

There is no data that needs to be transmitted. I mean I just need to transmit a heartbeat. If the controller misses the heartbeat, then it shuts down the process. The logic is fail-safe because there is no data being sent to act upon and no problem if the transmitter dies, the process simply shuts down.

Reliability:
As indicated above, either the transmitter stops because the float switch opens the circuit, or the battery has died. I can easily live with the process being stopped. I can not live with an overflow. I do not want to deal with the daily connection and disconnection of a sensor lead. It is a saltwater environment and the collection cup needs to be washed every few days. It will be fully immerssed in water to clean.

While the BT idea sound great, I would think it is a bit heavy for a simple heartbeat transmitter/reciever.


Last edited by beananimal on Tue Apr 19, 2011 9:04 pm; edited 2 times in total
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heizer74

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PostPosted: Tue Apr 19, 2011 9:01 pm    Post subject: Reply with quote

why don't u sense the weight of the cup?

no battery fault, no electronic waste uf the cup gets broken.


Last edited by heizer74 on Tue Apr 19, 2011 9:03 pm; edited 1 time in total
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beananimal

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PostPosted: Tue Apr 19, 2011 9:02 pm    Post subject: Reply with quote

heizer74 wrote:
why don't u sense the weight of the cup?


The cup is fixed to the filter via a twist lock flange. I don't wish to redesign the device, I jsut want to come up with a wireless level sensor that sends a hearbeat signal to the process controller.
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heizer74

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PostPosted: Tue Apr 19, 2011 9:05 pm    Post subject: Reply with quote

so why don't u sense the flow behind the pump?

allso ... no battery fault, no electronic waste if the cup gets broken
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beananimal

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PostPosted: Tue Apr 19, 2011 9:41 pm    Post subject: Reply with quote

heizer74 wrote:
so why don't u sense the flow behind the pump?

allso ... no battery fault, no electronic waste if the cup gets broken


The sensor (a simple reed based float switch) will be attached to the cup and connected to the waterproof transmitter package that is also attached to the cup.

I know it is possible to use a tiny transmitter to send a heartbeat that can be monitored by a reciever.

I want to know if such a "heartbeat transmitter" can be made so that it sends a heartbeat about once per second and do so for several months on a reasonable sized battery pack (AA or AAA). I am asking if anybody knows of a transmitter topology that fits these requirements. Once we get past that point, then we can deal with the AVR that will act as a reciever.

In the kindest way: I do not wish to redesign the filter nor I am concerned about electronic "waste" or a broken cup or a battery fault. Any advice to that end is not helpfull. If there is no way to accompolish the objective as I have outlined it, then I will look for other (less attractive) options.
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hgrueneis

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PostPosted: Tue Apr 19, 2011 11:26 pm    Post subject: Reply with quote

Even if you are able to put a transmitter to sleep for a second after transmition, it's not going to last for a year.
A picture or drawing would certainly help with this (nobody knows the physical dimensions or functions).
I have had good results with neodymium magnets and hall sensors.
There are small very cheap sensors available, if the filter housing is non magnetic then the sensor can be outside, the float with magnet inside..
Just a thought. Depending on size, the float can be a small plastic bubble or pingpong ball with the magnet in it.
An other possibility would be an inductive charger, like the RF-tag uses, just a bit more powerful.
Hubert
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Paulvk

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PostPosted: Wed Apr 20, 2011 12:20 am    Post subject: Reply with quote

I think having it on all the time is not the way to go and trying to re-invent the wheel is is not the best way. Now I would use a car/roller door remote type control and recever if you use a lithium battey for the car remote it should last 10years even the alkaline one in my remote is still going after 10 years, by wiring the remote press button to a float switch then use the recever to stop the pump you can get these units ready made for $30-60 US
here is an example from an australian shop that would work
http://secure.oatleyelectronics.com//product_info.php?cPath=47&products_id=186&osCsid=7c3b0c11d0df09b96091a9ba4bcd5ca7
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beananimal

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PostPosted: Wed Apr 20, 2011 3:55 am    Post subject: Reply with quote

Kindly, most of you are missing the basic question. The physical layout of the system and what it does are not at all imortant to my question. The system is not being redesigned and I don't need help sensing liquid level.

I will ask my question again in a much simpler form in hopes that I can get a more focused answer. Sorry if I have not been clear.

1) I want to transmit a simple heartbeat type of signal that can be recieved 1 or 2 meters away. I don't want or need to send data or any other type of information.

2) I want a controller (receiver) less than 2 meters away to perform a specific task if it does not sense the signal for 2 or more seconds.

I know that both #1 and #2 are possible. My question is can the transmitter for #1 be a battery operated device that has an expected battery life of 3 or more months?
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Ross_ValuSoft

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PostPosted: Wed Apr 20, 2011 5:49 am    Post subject: Reply with quote

I have come to this late ...

How about modifying an old car keyless lock transmitter?

Cheers,

Ross
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heizer74

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PostPosted: Wed Apr 20, 2011 8:51 am    Post subject: Reply with quote

well i've heared about 8051 derivates with very low powerconsumtion and rf
but i don't think this will be the best way to solve. good luck
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jenalcom

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PostPosted: Wed Apr 20, 2011 10:06 am    Post subject: Reply with quote

Why do people always want to overcomplicate things with electronics? Everything has got have a micro in it these days!!!

Keep it simple - a float switch, a length of two wire cable (perhaps with plugs and sockets in line) and a relay to switch the power on/off. End of problem - especially for two metres distance.

If you wanted to go a couple of hundred kilometres then thats a different scenario.
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