Simple wireless data transmission
eagletalontim
Posts: 1,399
A continuation of my power meter logger... I am now attempting to learn how to send a signal to the "main brain" of my project via a very simple wireless circuit. Every time the external sensor picks up an IR pulse, I would like to send a signal to the "main brain". Any simple schematics using minimal components available and have been tested with the PROP?
I have researched and found very simple AM transmitters using a single crystal but those all have 4 leads. I only have crystals with 2 leads.
I have researched and found very simple AM transmitters using a single crystal but those all have 4 leads. I only have crystals with 2 leads.
Comments
The nRF24L01+ transceivers are another inexpensive wireless option. I have info on these transceivers near the bottom of post #1 of my index.
I think you could run into legal issues if you try to transmit directly with the Prop. IIRC, there's too much noise on other than intended frequencies.
In general, with radio that works in the audio band, you should be able to debug it replacing the radio link with a wire link and a blocking capacitor (1uF greencap). And if it doesn't work with the blocking cap and wired solution it won't work with wireless. There was a long discussion a few years back on the picaxe forum about this - and the answer for sending data was first to send a preamble of the ascii character which was binary 10101010 and send about 12 of these first to bias the AC into the correct region. Then keep the packets short, or send every alternate byte as the inverse so the number of 1s and 0s is the same. Poor man's Manchester coding.
Then you can go up one level. Use a propeller or picaxe or similar to monitor the pulse as a digital input. Process than and send it out to something else via a serial link. Debug using wired serial links, then drop in RF transceiver modules to replace the serial link (these are about $10 on ebay). RF transceiver modules have an onboard microprocessor that does filtering and handles changing the baud rate.
I'm looking into similar things at the moment. I'm reading through this site http://openenergymonitor.org/emon/. They are taking things to a higher level - sampling the actual waveform and calculating the true power. And also monitoring the voltage and the current waveform which gives the current direction (my meter also has a little flashing led, but it doesn't tell me if it is 5kw in which is running my air conditioner, or 5kw export from the solar panels).
This stuff can get a bit complicated. I am tempted to go down the Arduino route as it has all been done before on that website. But I can see some scope for doing this with the propeller - maybe a propeller and an I2C ADC chip.
Are you using a Propeller to do the sensing? If so, a and you have some spare pins, there would be quite a few options to get that prop to talk to another prop - either by wire or by wireless.
The current sensor is a radioshack IR detector that is wired up to a 50ft cable run under my house out to the meter. There is no circuitry attached to the meter. Just the IR sensor and the wire running back into my house. I would like to eliminate the 50ft of wire and all the electrical tape that blocks as much sunlight to the sensor. (Beau helped me with the detection circuit in another post.) Now that I can have a "stand alone" circuit run on the outside of my house, I was hoping to eliminate the 50ft of cable which seems a bit expensive when trying to go wireless and accurate. Since the PROP calculate the distance in time between each IR pulse to calculate the current Watts being used, I need to ensure the data is not lost and the time between pulses is accurate according to the meter's IR output.
EDIT * : The reason I want to go with the simplest transmitter is to avoid using a PROP on the sensor outside. I plan to have this run via a small solar panel / battery and it needs to be able to run all night and even on cloudy days. The least amount of power usage, the better. I have several small 6V solar panels that I can use for the external circuit and a battery pack that holds 4 AA rechargeable batteries.
If you have already pulled the cable through, you might already have the best solution?! Just thinking of the alternatives - battery, solar panel, boxes for these, wireless tx/rx.
Thinking aloud, it does seem strange to need solar panels when you have all this energy nearby in the meter box. I've been thinking through what you need to measure power - current and voltage transformers etc and it all takes space. My meter box already is pretty full up. Your solution you have might well be the best. I like the way you are logging locally if the PC is off.
Little thing that clips over the led. Battery powered wireless tx. receiver in the house. Hmm - does it upload to the internet though? The arduino solutions do, and the ethernet shields are only a few dollars.
So many possibilities. I've also found some DIN mounted energy meters that give you the pulse output rather than needed to hook into the led. For 240V so not suitable for the US, but they are under $25. Depends if you are comfortable redoing mains wiring.
I reckon you are onto a winner with your design.
Perhaps an NRF24L01+ will do? I'm just about to check them out myself. I'd get one with a stick antenna. Low power, very cheap, easy to drive.
http://www.ebay.com/sch/i.html?_nkw=NRF24L01%2B
For longer range transceiver modules using lower ISM bands are better, like the RFM22
(which I think come in 433, 866 and 915MHz versions) You will need an external aerial
but that's partly why the range is much better. Simple 1/4 wavelength wire antenna will
do well.
RFM22's are a few dollars IIRC.
I believe there's code to run the nRF24L01+ from the Arduino. They can be controlled with an ATTiny chip.
When I did some range tests with the nRF24L01+ a few years ago and the only places I had trouble communicating between ends of our home was when a large appliance (oven, water heater, etc.) was between the two devices.
If the $2 version of the nRF24L01+ doesn't provide enough range, you could move up to the version with an antenna.