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226  Using Arduino / Project Guidance / Re: Ver...y long range communication on: August 04, 2013, 01:43:44 am
The only hope you have is to use a satellite phone on the robot.
Something like this.
Can get data rates up to 15 Kbs.
Hope you have a deep wallet.

227  Using Arduino / Sensors / Re: DHT22 sensor - humidity reading rubbish? on: August 02, 2013, 10:12:52 pm
This is good definition of RH.

228  Using Arduino / Sensors / Re: DHT22 sensor - humidity reading rubbish? on: August 02, 2013, 08:29:08 pm
Yes thats right.
For air at a fixed temperature, there is a maximum amount of water vapour that the air can hold before water will start to condense
out of the air.
In this case a RH humidity sensor will read 100%.
If the air is then heated, it can hold more water vapour, so the RH sensor will now read less than 100%.
The actual amount of water vapour hasnt changed.

There are other types of humidity sensors called absolute humidity sensors which read the actual amount
of water vapour in the air , but they usually read in grams per cubic meter, and as such arnt affected by the air temperature.

229  Using Arduino / Sensors / Re: DHT22 sensor - humidity reading rubbish? on: August 02, 2013, 06:38:39 pm
The DHT22 sensor measures RH (relative humidity).
Relative humidity is a measure of the amount of water vapour that air can hold at a given temperature.
If the temperature in a room goes down , then the RH in the room will go up, as the air which is getting colder
can now hold far less water vapour .
For a fixed amount of water vapour in the air in a closed space, such as a sealed room, then the RH will simply be an inverse
of the room temperature.
230  Using Arduino / Networking, Protocols, and Devices / Re: Aduino RF communication on: August 01, 2013, 06:20:45 pm
Radio communication is not 100% reliable, especially when using 434 Mhz , as its a shared frequency and you are competing
with anything else using the same frequency.
If you want 100% error free transmission, then you have to implement some kind of error checking or correction.
This means using 2 way communication between both ends to verify that the data is being received properly.
231  Using Arduino / Project Guidance / Re: Walkie-talkie made from Arduino on: August 01, 2013, 12:11:08 am
What range do you want from the walkie talkie?
Most of the radio modules that Arduinos can drive are low power and have limited range, usually a few hundred meters at best.
232  Topics / Home Automation and Networked Objects / Re: Garbage response controling a HDMI switch on: July 27, 2013, 08:44:15 pm
The problem may be that softserial is half duplex, ie it can send data or receive data but not at the same time.
If the HDMI switch sends back data at the same time you are sending data to it , then you will get garbage.
The fix is to use a hardware usart rather than softserial.
233  Using Arduino / Sensors / Re: Humidity sensors very inaccurate on: July 25, 2013, 09:25:44 pm
You may wish to have a read of this.

Its possible to reduce humidity with dessicant crystals.
You can buy them , or make your own as per the above article.
234  Using Arduino / General Electronics / Re: Tachometer vs GPS on: July 25, 2013, 04:38:56 am
A tachometer measures engine RPM.
Its not a speedo or odometer.
Even a speedo relies on a fixed known relationship between wheel speed and tyre size.
235  Using Arduino / General Electronics / Re: Tachometer vs GPS on: July 25, 2013, 01:09:43 am
Your question makes no sense.
A tachometer in a car measures the engine RPM.
To then determine the cars velocity requires additional input, such as the relationship between the
engines RPM and the wheel speed.
The cars velocity then requires information about the  tyre circumferance.
How accurate the speed is , depends on the accuracy of all this information.
236  Topics / Home Automation and Networked Objects / Re: Kambrook Remote Power Outlet & Arduino - working on: July 24, 2013, 04:57:12 am
Hi there.
Id appreciate the codes if possible.
I started doing what you have done last week, but no point reinventing the wheel.
Ive also decoded some remote control power points that Magnet Mart sell.
4 channel based on SC2262 / SC2272 chips .
My email is
237  Using Arduino / General Electronics / Re: Super mains hum detector.... on: July 23, 2013, 12:48:05 am
What you are trying to do is extremely difficult.
The problem is what is electrical noise?
Electrical noise is everywhere, not only when there is mains power connected to your house.
Unless you lived somewhere like the middle of nowhere, with nothing anywhere near you, you will always
pick up some kind of electrical noise.
If you try to detect only the mains frequencies like 50 or 60 hz, this will only work when your detecting device
is very close to a power carrying wire in your house, like a few inches away.

238  Using Arduino / Project Guidance / Re: Getting into radio on: July 23, 2013, 12:40:02 am
A better solution is to start by making yourself a simple radio receiver.
Its easy to make a simple crystal set that will receive AM radio stations.
This will teach you some basic fundamentals about tuned circuits and diode detection.
Here is a simple example of how to make one.
You could optionally add a small audio amplifier to drive a small speaker.
239  Using Arduino / Project Guidance / Re: Sniffing from 433 MHz receiver module on: July 22, 2013, 06:50:21 pm
Those cheap 433 Mhz modules are simple ASK receivers.
They dont know anything about baud rate.
What you are seeing on the data out pin is the digital equivalent of broadband noise
combined with whatever 433 Mhz signals there are in your area.
Unless you know specifically what you are trying to look for , its not possible to simply decode
whats coming from the data out pin.
Most applications that use these radios transmit known easily identifiable sequences that are easy to
find and decode, but you still need to know what they are.

240  Using Arduino / Project Guidance / Re: Getting into radio on: July 21, 2013, 10:48:22 pm
Building Radio Transmitters that actually work, ie have efficiences of 50% or more is not a trivial
exercise, and requires a good understanding of impedance matching networks , and an understanding of antenna design.
The ARRL handbook is not a bad start, but the learning curve is steep.
If you are looking at building Transmitters in the UHF or SHF bands , 400 Mhz up to 2.4 Ghz
I would say forget it initially, as its not usually practical for a home hobbyist.
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