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41

A reflector might accidentally be substituted by some reflective aspect of an obstacle, say a chrome plated fender on a bicycle, motorcycle, classic car... or even the reflector on one. In contrast a transmit receiver pair is far more likely to indicate the true and complete path.


22

A white card placed in the beam close to the transceiver end will fool the beam. A transmitter-receiver pair across the space to be protected is much more resistant to defeat in this fashion.


14

The typical LiftMaster/Chamberlain safety sensor system is designed to prevent it being accidentally or even easily deliberately disabled. Interposing a reflector, an electrical short or an electrical open anywhere external to the controller will not provide a false 'clear' signal. In fact no combination of passive components connected to the sensor ...


5

You're using a bipolar 555 and the original obviously has a CMOS TLC555 (marked TL555). There are a number of differences aside from power supply current draw including greater output swing (particularly noticeable on a 5V supply). Diode on the original is probably a 1N4148 or similar. A 1N400x is too slow for this application. I would expect C1 to be more ...


5

Most thermistors used for measuring temperature are NTC. They are specified relatively tightly in terms of their parameters for that application. They usually change quite a bit with temperature, of the order of -5% for every degree C, so that they end up being very nonlinear, to the point that for a wide temperature range you need a lot of dynamic range in ...


4

Back EMF is always generated any time the rotor is moving. The back EMF for the phase wire that is not being driven can just be ignored if you are doing 6 step commutation with hall sensors. The part of the H-bridge connected to that phase wire will have top and bottom fet off so no current will flow, and the back EMF sees an open circuit. The magnitude of ...


3

Am I using this instrumentation amplifier in a wrong way ? Quite possibly (from your schematic). As with any (maybe most) Instrumentation Amplifiers you need some DC bleed resistors down to 0 volts (mid rail) to remove bias currents because the inputs don't like to float: - Bottom right is the picture I would reference in your particular case. Try 1 Mohm ...


3

Those are decoupling capacitors. They filter out ripple voltages. The reason for 0.1 uF is that they tend to filter out wide range of frequencies better than in pF or nF range capacitors and 1uF or higher capacitors are larger in size so they are avoided because of that 0.1 uF has usually used. Finally 0.1uF are cheaper and easily available.


2

You have to apply higher-order polynomial regression (second-order is enough) for establishing the relationship. There is a built-in function in Matlab and GNU Octave for establishing the relationship. Besides, you may apply gradient descent to find the relationship (which is really tough). I always use Octave for algorithm development. It's free and just ...


1

I haven't chose a sensor yet, but it does need to be the type where it clamps around an existing wire. Hall effect sensors work by detecting magnetic fields. I've never heard of a magnetic field sensor being damaged by too strong of a magnetic field. (Within reason - of course if it was extremely strong like an MRI then it might suck the sensor in and smash ...


1

I never really answered the question. The capacitors referenced are decoupling capacitors. Decoupling means isolating the local circuit from the supply. As in, decouple IC impedance from source impedance. I've always looked at decoupling capacitors as a bucket of electrons placed close to loads. Typically, you need a small one for quick response and a ...


1

PTC thermistors are used when you want to increase the resistance offered with an increase in temperature. NTC is used when you want to reduce the resistance for an increase in temperature. PTC thermistors are used as resettable fuses in circuits. When the current flow increases, the temperature increases, and the PTC thermistor resistance increases, and the ...


1

Important Note- the above circuit is only applicable when all the resistances are nominally at the same value i.e. the same magnitude balance current flows into both R1 and R2. I'm mentioning this because if the left half of the bridge has a different impedance to the right half, 3-wire connections to an external device don't produce wire-resistance ...


1

If you cannot put a dye in the liquid the only alternative I can think of is to make sure the beam from the chip hits the surface of the liquid at an angle that will guarantee some reflection. In order to recover the reflected beam you would also need to factor in a mirror to return the reflected beam to the chip.


1

Instead of a retroreflective prism or tape, a set of mirrors could return the beam to the combined transmitter and receiver that receives a beam from above. That would overcome the "safety" objections posted by Luddites above. Three simple flat mirrors at 45 degrees is all it takes-- no wiring. Of course my trailer hitch would still interrupt ...


1

The main reason, for using a through-beam sensor for a garage door, would not be cost but safety, reliability and trouble-free operation. A retro-reflective sensor could be considered unsafe for this application, should one take into account the rare event of it responding to the reflection from an obstacle. For a through-beam sensor, the actual distance ...


1

The 1 megaohm source resistor and comparable input impedance of your scope with a 1x probe form a voltage divider preventing the test signal from reaching more than about half value. Remove the scope probe - this circuit is too sensitive. If you must try to probe use a 10x probe, but it would be better that you have nothing extraneous connected to the test ...


1

Suitable alternatives: NXP KTY81/110,112 Thermistor SOD70 1.01kΩ, 5.2 x 4.2 x 4.8mm (very similar specs, slightly bigger casing) KTY83-122 silicon temperature sensor (recommended by bldc motor controller supplier/seller)


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