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481  Using Arduino / Sensors / Re: Help with 433mhz receiver on: August 12, 2012, 06:12:44 pm
When using the oscilloscope idea to capture the data you need to know exactly when the sensor is transmitting
as the transmissions are very short, usually 100 milliseconds or less.
This means that you will need some kind of way of determining electrically when the sensor is sending
and then gating the data from the receiver to the oscilloscope.
Also, the data pin on the receiver is designed for driving a high impedance load so it needs to be connected
to something that wont load it , like a hi impedance cro probe.
You should be seeing on the oscilloscope a rectangular waveform toggling between 0V and Vcc, which will be there all the time.
Have a read of this
http://wmrx00.sourceforge.net/Arduino/OregonScientific-RF-Protocols.pdf
Whilst its not for your sensor, it will give you some understand of how these sensors work and how they transmit and what you should be looking for.
482  Using Arduino / Sensors / Re: Help with 433mhz receiver on: August 12, 2012, 01:28:18 am
What sort of weather station sensor are you using.
The trick with these things is figuring out where the data starts and what it means.
They generally also send some kind of sync bytes and some kind of CRC.
The sync bytes come straight after the flag sequence, and then usually the data, followed by the CRC.
An easy way to look at the data is to download a PC oscilloscope program which allows you to see
whats coming out of the receivers data port using your PC sound card as an input.

483  Using Arduino / General Electronics / Re: Solar Panel energy to DC on: August 11, 2012, 06:24:01 pm
Lipo batteries must not be overcharged otherwise they will be destroyed.
4.2 volts is the maximum voltage that the battery can be charged too, then you need to stop the charging process.
It would be easier to use 3 AA size nimh batteries as these can tolerate overcharging as long as the charging rate
is C/20 or less.
484  Using Arduino / Sensors / Re: Help with 433mhz receiver on: August 10, 2012, 06:24:49 pm
These types of receivers are extremely simple amplitude modulated types which produce "data" all the time
on their output data port,even with no signal being received.
The "data" is simply the digital component of the noise input when there is no Rf signal present.
You have to use them with some kind of data decoding logic to separate the real data from the noise.
Most weather station sensors send a long sequence of alternating bits at the start of the transmission
to allow the receivers AGC (auto gain control) , to adjust , and they also usually use some kind of Manchester coding
to ensure a 50% logic level.

485  Using Arduino / Motors, Mechanics, and Power / Re: 24V BLDC Motor + Dual FETs + Arduino on: August 05, 2012, 11:29:22 pm
What value resistors are in series with the gates?
You have to also take into account the time it takes to charge and discharge the gate source capacitance
which will be indicated in the fets data specs.
486  Using Arduino / General Electronics / Re: Trouble with a boost converter on: August 04, 2012, 09:38:40 am
If all you need to do is turn the converter on and off, the connect the Arduino output to pin 3 which is the shutdown control.
Converter runs when this pin is grounded, stops when this pin is high.
Connect the switcher chip Vcc to a decent 5v supply.
487  Using Arduino / General Electronics / Re: Trouble with a boost converter on: August 03, 2012, 06:16:52 pm
Only boost or inverting converters initially draw large amounts of current to start.
Buck converters (reducing voltage) arnt as bad as the switch is in series with the load.
But , any switching converter will have trouble starting when fed from a current limited
source like an Arduino output pin.
488  Using Arduino / General Electronics / Re: Trouble with a boost converter on: August 02, 2012, 09:06:21 pm
Your circuit cant start.
If you look at the specs of the switcher chip you are using, the minimum peak switch current is 0.65 A , typically 0.9 A
which is well above what the Arduino can supply.
These types of switcher chips are designed to run from batteries which can provide the initial current to start the switcher.
Once its oscillating, the current drawn is then determined by the load.
You need to supply the switcher chip with a 5V source that has at least a 1 A current capacity to get the switcher chip started.
489  Using Arduino / Motors, Mechanics, and Power / Re: Having probles biasing FETs in an inverter circuit. on: July 26, 2012, 01:44:31 am
You need to think this whole project through more thoroughly.
Its important to know what the Inverter is going to power as feeding a square wave into a 50 HZ transformer
will not produce a very friendly waveform.
Typically, small Inverters for converting 12 V to 230 V dont work like what you are designing.
Usually, the 12 V is stepped up to 310 V using a push pull Inverter running at around 25 KHZ using a ferrite core
transformer, and then the output is rectified to produce 310 V DC , which is fed into a high voltage H bridge
designed to produce a MSW (modified square wave) output.
Even then, its important to know what the Inverter is going to power, as some devices dont like square wave power.

490  Using Arduino / Motors, Mechanics, and Power / Re: Having probles biasing FETs in an inverter circuit. on: July 26, 2012, 01:17:13 am
Really need more Information.
What is the Inverter powering.
What is the ultimate output voltage, and power capability.
491  Using Arduino / Motors, Mechanics, and Power / Re: Having probles biasing FETs in an inverter circuit. on: July 25, 2012, 05:44:03 pm
Yes, the hi side fets dont their sources grounded, so the gate voltage has to be higher than the supply voltage, by whatever is needed to ensure
that the fet saturates properly.
As well, you have to turn all the fets on and off quickly which means that the gate source capacitance has to be charged and discharged quickly
and as well you have to prevent shoot through all of which a h bridge driver does for you.
492  Using Arduino / Motors, Mechanics, and Power / Re: Having probles biasing FETs in an inverter circuit. on: July 25, 2012, 05:18:23 am
You arnt turning the hi side fets on properly.
You need at least 10 volts between the gate and source to turn the fets on, and that means that if you only have a 12 V supply
you need at least 22 volts to turn on the hi side fets.
Google H bridge driver to find a suitable driver chip for your circuit.

493  Using Arduino / Project Guidance / Re: PV cell energy monitoring on: July 24, 2012, 08:07:30 pm
Are you trying to measure the maximum power output of the cell , or are you just trying to measure the variation over time .
Solar Cells only deliver maximum power at one point on their V / I graph, and using a simple load like a resistor or current sink
will not give you the absolute maximum power output.
It will work if all you are looking for is relative changes over time.
To extract the maximum power from a Solar cell you need some kind of peak power point tracking.
This explains what the problem with Solar cells is and why peak power tracking is needed.
http://en.wikipedia.org/wiki/Maximum_power_point_tracking
494  Using Arduino / General Electronics / Re: Protected LIthium Ion Charging Circuit on: July 23, 2012, 10:51:52 pm
A bit more detail on how the individual cells are protected from over / under charging would help.
Charging Lipos in series needs cell balancing circuitry and its unclear from your description whether this exists
or not.
495  Using Arduino / General Electronics / Re: P-channel MOSFET won't turn off? on: July 21, 2012, 06:40:33 pm
If you are using a ATmega32 or similar Atmel chip, the high output voltage of an IO pin
is only guaranteed to be greater than 4.2 V with a 5 V supply.
You cant guarantee it will be exactly 5 V.
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