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31  Forum 2005-2010 (read only) / Interfacing / Re: detect presence of stationary persons on: January 12, 2010, 12:08:02 pm
I already have some DS18S20 sensor and already found they are influenced by nearby heat emissions, so it's a nice idea, however if you want to connect it to a PC it requires a 1-wire master like the DS9097U that costs around 14 euros.
For that price I could buy a ultrasonic SRF02 + MAX232 or similar chip, the module needs 4mA power and MAX220 0.5mA, probably I can power it directly from the port.
If I add a FTDI FT232R USB to RS232 chip the bill goes to 20 Euros just for the components, and it becomes to be harder to justify as a power saving solution

IR reflection would be much cheaper, unfortunately Seedstudio is located in HK and I'd prefer to buy in the EU because the custom is too slow.
Here I've found this interesting page
32  Forum 2005-2010 (read only) / Interfacing / Re: detect presence of stationary persons on: January 11, 2010, 07:36:31 pm
Thank you Groove for the advice.
I found SRF02 sensor is perfect, it has also serial connection which is useful as I'd like also to wire it directly to a PC.
However it's a bit too expensive. Is there anything else I can try to detect a human body? I don't need precise distance measurement, just to know if it's in range or not.
I was thinking on a PIR detector like the Murata one that measure average IR light detected, then a comparator detect if the threshold is too low and outputs a low signal that can be read as a digital input.
33  Forum 2005-2010 (read only) / Interfacing / detect presence of stationary persons on: January 11, 2010, 10:12:25 am
Hello friends,
I need to detect the presence and the absence of a person in front of a display. Traditional PIR sensors with prismatic lens are useful to detect motion, but if people are stationary they are invisible to it.
The range should not be very high, it's enough a distance of 1 meter or less.
Do you have any clue on how to do it? Can a PIR sensor like the Murata IRA-E700ST0 without lens work?

34  Forum 2005-2010 (read only) / Interfacing / Re: High powered RGB LED - where to buy on: September 20, 2009, 11:49:29 am
Which way are you using to power them?

I'm interested in LED lighting too and there are two different schools, the ones who just use a MOSFET or a transistor like ULN2003 (useful for RGB models) and the ones with constant current drivers, which seems to preserve LED's life but also more complex.
35  Forum 2005-2010 (read only) / Interfacing / Re: Can an optoisolator do this or do I need a relay? on: January 05, 2010, 07:40:44 pm
There is a schematic on the Playgroundwith a relay driven by a transistor triggered by an optoisolator

36  Forum 2005-2010 (read only) / Interfacing / Re: interface RS-232 GSM module on: January 04, 2010, 04:21:57 pm
Thank you for the reply!

I read there are several MAX232 clones, like ones from ST and TI that can cost 10x less. Can I go away with them or better to stick to the original one?
37  Forum 2005-2010 (read only) / Interfacing / Re: interface RS-232 GSM module on: December 30, 2009, 06:01:51 am
Great, so I just need a MAX232 and power it through the Arduino +5V, am I right? I read MAX233 is the same but without external caps. Where is the downside? I suspect it's about the cost, as the 233 costs twice the 232...

Thank you for the patience, I'm a bit more on the software side - in fact I already learned all the necessary AT commands through a GSM USB modem..
38  Forum 2005-2010 (read only) / Interfacing / Re: interface RS-232 GSM module on: December 28, 2009, 07:46:05 pm
Thank you kg4wsv for the reply!
Yes you guessed it, it's a Sipex SP3239ECA 3.0 to 5.5V RS-232 transceiver.
As Arduino have already 5V signals, can I wire it directly to the GSM module?
How can I wire it?
I don't understand why the used a 3 to 5.5V chip when computer's RS-232 signal voltage is +12/-12V
For convenience this is the DB9 RS-232 pinout
39  Forum 2005-2010 (read only) / Interfacing / interface RS-232 GSM module on: December 28, 2009, 01:24:00 pm
Hello Friends
I've bought this Siemens TC-35i GSM module:

However I don't know how to wire it to the Arduino, I didn't find anything on the Playground except software related things.

Does it need any chip (usually from Maxim) for voltage translation? I read Arduino 2009 has UART TTL 5Volts serial connection on Pin 0 and 1.
Any protection diodes for ESD?
40  Forum 2005-2010 (read only) / Interfacing / Re: Help Creating A Long Range Sensor on: December 22, 2009, 07:47:11 pm
802.11b is way too slow and insecure.
I think 802.11g it's the more mature wireless standard, I suggest you the D-Link DWL-2100 because it's one of the most versatile access points (have five operating modes including repeater and wireless client) and has a reasonable price. I had good experience putting 4 of them in a big house all connected through ethernet cable, you can move through the house and the download never stops.
However someone else are recommending Linksys WRT54GL for point to point applications, as it has a standard antenna connection.
There are also 200mW access points but they are expensive and probably legal only in the US.
I missed the part you have a moving target. You said you can narrow the reception angle to 90°, then you can use a sector antenna. You could even built it by yourself, there are some pretty guides on the net. Someone made an antenna from a Pringles can!
However if the movement is too random you should use a GSM module, then it could be even on the other side of the country smiley-grin
41  Forum 2005-2010 (read only) / Interfacing / Re: Help Creating A Long Range Sensor on: December 21, 2009, 12:08:58 pm
use a couple of wi-fi access points with directional antennas.
you can reach kilometers without worrying about legal restrictions or special licenses. the laws usually say you can't transmit more than 1W power, but don't say anything on how you radiate it. If you need more transmit power you can apply for a Amateur Radio license smiley
Then you connect your Arduinos through ethernet modules.
42  Forum 2005-2010 (read only) / Interfacing / Re: Detect optical pulse from water/gas/elec meters on: November 07, 2009, 09:37:56 am
Very interesting and a cheap way to measure consumption from electronic meters for electricity we have in Italy

There is a topic also for meters with reed switch like the methane gas ones.
43  Forum 2005-2010 (read only) / Interfacing / 4016 as audio switch + relay drive on: December 23, 2009, 09:11:19 am
Hello friends
I need to remotely switch the audio signal and the power to a pair of speakers.
As Grumpy_Mike suggested I'd use a 4016 in analog mode.
The DS2413 is a 1-wire switch with two channels that can sink 20mA each
I'd like to add also a mechanic relay to switch off the speakers amplifier when not needed to save power.
The relay would be powered through a transistor where one or both channels are high.

Have I wired the transistor correctly? I know that usually base act as a control switch and emitter should connect to ground, however DS2413 sinks, not source. Do I need a PNP transistor for this?

How can I supply -5V for 4016 analog mode? I have only +5V and GND.

Thanks and merry Christmas to everybody!
44  Forum 2005-2010 (read only) / Interfacing / Re: Help using an H-Bridge on: December 21, 2009, 12:32:11 pm
you could use an external transformer, there are some cheap ones with selectable voltages, or if your application needs to be wireless, use a battery pack as Ran suggested.
There are plenty of them in model building shops, with various capacities and technology (NiMH or LiPo)
45  Forum 2005-2010 (read only) / Interfacing / Re: laser based intruder detection on: December 23, 2009, 05:49:54 am
Yesterday night I tried the red laser with the LDR I already have and has pretty fast response time.
Plus the resistance change was big even with all the lights on in the office, so if I put it into a black box with a hole it should be immune to daylight interference
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