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Claus Wahl
Claus Wahl 14 hours ago
Exactly, oetelaarNG. To make it simple and either intuitive (pull the handle should be ok) or well guided.  I believe that Elektor needs to better explain what could be done to the exterior and what is not OK. Could the door have a drilled hole? Could a well integrated screen be recessed in the door or the frame? If no modification at all is allowed on the exterior, most of the suggestions are breaking the 'design rules'. It seems like a camera is out as it will have to be wisely placed? Even a voice-system will be difficult. We still have knocking and pulling the bell, but advanced use of these inputs *will* require some guiding for the visitor, eg with a note. But then, why not make a nice naming plate with some touch input and communication device? If some form of recessed mounting could be accepted: Occasional users, old folks etc should be comfortable using it: Pull the handle, activate a screen with info and touch/keys and place the call. When not in use, the overall color and appearance match the door or frame.  
Invisible Multi-Target Doorbell
karim rihani
karim rihani 16 hours ago
Lead Acid Battery charger 
Battery Charger Next Generation: request for comments
Bastelfix
Bastelfix 17 hours ago
Hy! I build the unit and it works. But i have a problem with the linearity. For example: i used a calibratet RF Power Source for calibration. -calibration at 140MHz and RF Level-20dBm -calibration saved now the following measurement when changing RF Level at the input (all without attenuator) : RF Level at Input:                Display Power Meter: 0 dBm                                     -11,0 dBm -5 dBm                                    -13 dBm -10 dBm                                  -15 dBm -20 dBm                                  -20 dbm   (calibration point) -30 dBm                                  -24 dBm -40 dbm                                  -28 dBm -50 dBm                                  -32 dBm What could be the problem? Is there a conversion factor not correct? Best regards, Sven
RF Power Meter with 1MHz-10GHz bandwidth and 55dB dynamic range
ClemensValens
ClemensValens 17 hours ago
Good point: it must immediately be clear how to use the system.
Invisible Multi-Target Doorbell
oetelaarNG
oetelaarNG 1 day ago
You are assuming that someone will instantly understand how all this high tech stuff works. I think this assumption is wrong. A doorbell should be a doorbell (in my opinion). Maybe the answer should be simple, use the original pull-handle, attach a switch. A little note on the side "Pull one time for company-1, pull 2 times for company 2"  I can not imagine many more businesses behind one door. A little circuit, based on a microprocessor (small arduino) can be used to time the interval between the pulse(s) and actuate one of the small relays (one per company) to sound a bell.  
Invisible Multi-Target Doorbell