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31  Using Arduino / Project Guidance / Re: House plant watering bot on: August 15, 2014, 06:25:32 pm
Why do you need to know if watering has happened x days ago.
Surely, if the soil moisture sensor is showing inadequate moisture, then you need to water.
32  Using Arduino / Networking, Protocols, and Devices / Re: 2 rf modules on: August 13, 2014, 06:33:38 pm
OK, you will have to look at whether VirtualWire can operate in full duplex mode .
I dont think it can.
The problem with those cheap modules, is that you have to pre process the data with some program running in the Arduino to make them work reliably.
Most people use Virtualwire, but only for 1 way transmission.
33  Using Arduino / General Electronics / Re: MC34063 buck with large variable input? help on: August 13, 2014, 06:28:14 pm
The limiting factor apart from the chips voltage and current limits, is the inductor saturation current.
If you design the circuit based on the highest input voltage at maximum output current , then it will be Ok at lower input voltages.
34  Using Arduino / Networking, Protocols, and Devices / Re: 2 rf modules on: August 12, 2014, 07:59:25 pm
Your question makes no sense.
If what you mean is can I have a system where I can send data and receive data at the same time using those types of modules
the answer is no, you cant.
If you want to send data in both directions , you need better radio modules , such as Xbees or NRF24l01 .
35  Using Arduino / Project Guidance / Re: Arduino Oscillator on: August 12, 2014, 06:00:16 pm
Normally using a standard CRO probe to measure the frequency of a pierce type crystal oscillator will pull the crystal
and lower its frequency as the probe adds parallel capacitance.
Most Micros use pierce type oscillators.
If you have an active FET probe then its OK .
36  Using Arduino / Networking, Protocols, and Devices / Re: I cannot get SoftwareSerial to work on: August 07, 2014, 06:26:38 pm
Are you using 2 Arduinos.
Software Serial is 1/2 duplex and cant send and receive at the same time .
37  Using Arduino / General Electronics / Re: Regulation of water flow on: August 03, 2014, 09:57:14 pm
A cheap source of rotary ball valves, which is what the OP needs can be found in battery operated garden hose timers
which you can buy at any hardware store.
You have to pull the timer apart, and remove the ball valve.
They usually run off 3V or 6V, depending on the type of timer.
38  Using Arduino / General Electronics / Re: RR3 RF receiver on: August 03, 2014, 08:17:07 pm
Those 433 ASK radios generate a lot of noise , as you are seeing.
To determine what the keyfob is sending, its much easier to pull the keyfob apart
and connect the Arduino to the data pin of the transmitter in the keyfob.
That way, all the noise is removed, and you get a clear indication of the transmitter data
which makes it easier to decode.
39  Using Arduino / Project Guidance / Re: MPPT Solar controller - based on Tim Nolan's ideas on: August 01, 2014, 07:15:50 pm
MPPT controllers are expensive , but theres no reason why they need to be .
Theres not much in them in the way of electronics.
I would guess its the small market.
As to why MPPT controllers make a differance, you need to understand how Solar panels work.
For example , a 12V solar panel isnt really a 12V panel at all.
Its really a somewhere in between 12V and 21V panel depending on what load is connected to it and how bright the sunlight is.
Solar panels will only deliver their rated power at one specific voltage and load, and this voltage and load moves around as the
sunlight intensity changes.
The ones Im using are rated at 100 watts STC , 18V at 5.5 amps.
What does this mean?
The STC means that panels power rating is measured at 25D cell temperature with a irradiating intensity of 1000w/sq meter.
The 18 V @ 5.5 amps means that the Solar panel wants to see a load of 3.2 ohms.
With any other load the panel will deliver less than 100 watts.
If the load is a 12V battery, the panel will only deliver 66 watts as the battery clamps the solar panels voltage to 12 V , but the current stays the same at 5.5 amps.
This happens because Solar Panels behave like current sources, so the current is determined by the available sunlight.
The Solar panel is now  behaving like a 66 watt panel.
All a MPPT controller does, is fools the Solar panel into thinking its still connected to a 3.2 ohm load, so the battery gets the full 100 watts.
At differing levels of sunlight, you get less improvement, so if you live somewhere, where you never get 1000w/sq meter, there wont be as much differance.
All grid Tie Inverters, which are the type that are used by roof top solar systems to feed power back into the grid have MPPT trackers in them , as the improvement gets better economically the bigger the installed panel capacity.

In its simplest format , all a MPPT controller needs is a small micro, 1 Power FET, one inductor,a couple of transistors,one or 2 diodes ,one opamp,a current shunt, and a small number  of resistors and capacitors.



40  Using Arduino / Project Guidance / Re: Project parameters r/t a wireless greenhouse controller on: July 31, 2014, 10:55:40 pm
Everything you want to do is possible, but you would be much better looking at one of the larger processors like the Mega or even a Duo, to make sure there is enough memory to handle your code.
The requirement to control everything via a web browser, will really chew up memory .
41  Using Arduino / Project Guidance / Re: MPPT Solar controller - based on Tim Nolan's ideas on: July 31, 2014, 02:46:42 am
You get roughly around 25 - 30% improvement in power input to the battery, at least that what I get from my
home made MPPT charger.
The cost / effort needed depends a lot on how much power is available from the Solar Panels and how big the batteries are.
Mosfets are very easy to blow up if you get something wrong , you have to be very careful.
Tim Nolans design is a good one to start with, but be very careful if you start changing the design.
Mppt charge controllers need a fair bit of design work to make sure you arnt stressing the Mosfets,as if you do
they will either blow up the instant you turn it on , or after an hour or so.

42  Using Arduino / General Electronics / Re: Usb to uart and 433MHZ on: July 30, 2014, 01:33:23 am
That will work OK.
Those 433 Mhz receivers produce a lot of noise on their data pins , so you will need some kind of protocol
in your PC to detect your transmitted data.
43  Using Arduino / General Electronics / Re: Usb to uart and 433MHZ on: July 29, 2014, 05:33:53 pm
What are you intending to use the modules for.?
They need some kind of signal processing like Virtualwire to work properly.
Usual way to use them is with an Arduino at both ends, and then you connect the receiving Arduino to your PC.
44  Using Arduino / Motors, Mechanics, and Power / Re: Lithium-ION-POLY Batteries.... etc. on: July 29, 2014, 12:24:30 am
I use them a lot.
Pretty useful and longer lasting than NIMH.
However, you must not overcharge them , or over discharge them .
ie no more than 4.2 V when charging and no less than 2.8 V when discharging.
The protected ones are more foolproof.
Also, be careful of the stated capacities, as there are a lot of fakes, especially if you are buying them on Ebay
or from Chinese sellers.
Anything over 3300 mah , unless its from Panasonic,Sony  or Sanyo, is likley to be a fake.

45  Using Arduino / General Electronics / Re: Wind generator for 12v battery - no controller? on: July 28, 2014, 02:38:43 am
You dont need a charge controller with a tiny Solar panel, as the battery will simply clamp the Solar panels output
to whatever the battery voltage is.
If the Solar panel can only make 250 ma , then as long as the battery is at least 2.5 ah or more , it will never be overcharged.
You only need charge controllers with large solar panels that can make 100s of watts, or if you have a tiny battery.
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