74

This IR signal is indeed ignored by the AM radio. However, an AM radio is very sensitive the radio waves (yeah, DUH! ;-) ) When the IR remote operates (you push a button) the chip in the remote will switch on a clock resonator circuit which it needs to generate the IR signals. I have seen most IR remotes using a 455 kHz resonator. This is simply used ...


56

The simple answer is that they are using near IR. LED manufacturers have a good handle on how to make them so they are affordable. Their center frequencies may be invisible to the M-1 eyeball (i.e. human eye), but unless they put a filter in front of the LEDs (which cause them to produce less illumination) there will be some of it that you can see. ...


24

People often use imprecise terms to describe InfraRed and it is further complicated in that with respect to Infrared "that word infrared ... I don't think it means what you think it means" in a lot of cases. PIR - AKA Passive infrared sensors are pryoelectric devices that are optimized to detect Mammalian body temperatures (around 300 K), these warm bodies ...


23

Side by side: - The receiver will be slightly off centre compared with the transmitter (purple lines I added are sitting at 950 nm) but the receiver will still be above 80% of its optimum sensitivity. You should also consider that as the emitter warms up, the peak centre emission can move by 0.3 nm per degree C so, if it warmed 40 degC, the peak wavelength ...


22

[ added 2_D resistor_grid methodology for exploring shielding topologies ] You want that IR receiver to respond to photons, not to external electric fields. Yet the photodiode is a fine target for trash from fluorescent lights (200 volts in 10 microseconds) as the 4' tube has that restrike-the-arc action 120 times a second. [or 80,000 Hertz for some tubes] ...


21

There are two different frequencies, in two entirely different contexts, involved. The infrared light generated by an infrared LED is in the 300+ GHz range, this is correct. For instance, the TSAL5400 IR LED often used in remotes has its radiation peak at 940nm wavelength, i.e. 318,930 GHz. However, IR remote controls do not output continuous infrared ...


20

The gate resistor on a MOSFET is really there to protect whatever is sourcing the current. Much like a discharged capacitor, the gate will initially look like a short to ground when voltage is first applied. A MOSFET with a very large gate capacitance can sink a very large amount of current for a short period of time. If you're driving the gate with, say, a ...


19

Yes, your system will work. Consider the system spectrum (red line below), which is each sensitivity at each wavelength times the emission at that wavelength. You can see that the transmitter is operating on a 0.84 efficiency portion of the receiver, which ought to be well within any error margin you might have, considering losses for distance, misalignment,...


16

Simple, silicon devices are very sensitive to infrared light. See the wikipedia article on a photodiode, there's a graph showing that silicon photodiodes are most sensitive around 900 nm, and that is near infrared light. Silicon devices are sensitive to visible light so the package has to block all the light.


15

The transition from visible wavelengths to invisible is not infinitely abrupt. Your eye's sensitivity falls off in the IR range. But in the near IR, it may not be zero sensitivity. And the emission spectrum of LED's is not infinitely narrow. So not all of the photons coming off of an LED have the exact same wavelength. The net effect of these two things is ...


15

The codes are just a reference to a set of actual IR codes. It tells the microcontroller or CPU (loose term) of the remote which type of code modulation, brand and device type to use. The standard protocols are RC5 and NEC, though there are other types. Once you know the protocol, the rest is just crafting the actual button code, which is a fairly small set ...


14

After working with IR for years, and observing numberless products, I conclude that the reason just: tradition, and a bit of aesthetics. But with a caveat. For receivers, the bandpass window is critical for rejecting the visible band: sunlight and bright room lighting. Even when using modulation, filters, and synch detectors, and with IR-sensitive ...


13

If the requirement for hacking a ready-made device can be dispensed of, a low cost and simple to implement range sensor option is: Use a 405 nanometer blue laser as a projection element. These are available for around $13 on eBay: Use epoxy potting compound to waterproof the module - the lens mounting is already waterproof, don't use epoxy on the lens. ...


13

I fixed my problem, here is an explanation for others: I connected one pin of the IR transistor to ground, and the other to both Analog pin 5, and to a 210 Ohm resistor leading to 5v. Then I used this code: int analogPin = 5; int val = 0; void setup() { Serial.begin(9600); } void loop() { val = analogRead(analogPin); delay(1); if(val&...


13

The cover is made of plastic that is opaque to visible light but transparent to infra-red. It probably attenuates the infra-red a small amount but not enough to affect operation. The cover is basically for aesthetics - it will work fine without it. Learning remote controls also have an IR photo-diode where there may be some advantage to filtering out ...


12

The forward voltage for an IR LED is much lower than for a visible light LED, typically around 1.3 V, but rising if you push real high currents through them, like > 100 mA. There seems to be no reason why you couldn't place two of them in series, especially if your Vcc would be 5 V. If your Vcc comes from a pair of AA batteries though, the voltage drop of ...


12

3 come to mind. An IR encoder as RoyC mentioned. Paint the back or sides of the weights alternating white and black. A camera as you already mentioned. OpenCV would make quick work of this. And You can do it at a distance without touching anything on the machine. And the last option is an actual weight sensor. A load cell placed under the weights. When ...


12

The LED in a smoke detector is safe to look at. Not only that, but the smoke detector is constructed in such a way that the light of this LED does not actually escape the device. It is hidden away in such a way that light can't get in from the outside, as this may disturb the sensor's ability to detect the smoke. This structure works both ways, and hence the ...


12

From the TI LM358 datasheet, the maximum output slew rate of your op-amp is about 0.3 V/us: Your scope trace shows the signal has a slope of about 3 V per 10 us, pretty well matching the datasheet limit. This is simply the fastest edge an LM358 is able to produce at its output. To achieve a faster edge, you'll need to choose a different op-amp.


12

Figure 1. Image source: Adafruit. The data is modulated on the 38 kHz carrier as shown in the image above. The 38 kHz is transmitted in bursts and it's the bursts your camera is detecting. You are correct that your camera's sensor will integrate many 38 kHz pulses in one video exposure "frame". Having the carrier frequency makes the system much ...


11

As with any LED, you should be concerned with the LED current, much more than its voltage. The voltage across any forward-biased LED (any diode, really) will be governed by the diode, and will only vary slightly with current. Look on the LED's data sheet for the recommended operating current, or, failing that, the Maximum Recommended current. If you can ...


11

Most likely, your radio is picking up unintended EM radiation from the remote's circuitry. You mention that it operates between 30 and 38KHz, but the IR probably uses square wave modulation, so you'll still pick up the harmonics. Of course, it could be some other signal than the LED drive getting picked up. Once you have a signal or harmonic near the ...


11

For bulk material, you might try a slab of germanium. It's not a metal, but a metalloid, resistivity about 1 Ωm in its pure state, but will improve dramatically with doping, which may not affect its IR transparency in the 8 to 13 µm range. However, germanium is quite expensive and hard to come by. If it's not an imaging sensor, then you could simply use a ...


10

Idea 4: This will give you the best accuracy. You will need the following: 2x Precision linear slides. 2x Precision linear encoders. 2x Metal linkages. Attach a linear encoder to each linear slide. Arrange the two slides 90º apart, and attach the object to the sliders using the linkages. Linear encoders like this are used for precision measurement ...


10

The simplest way to connect a photodiode (even an LED can be used in this way as a photosensor) is as below: simulate this circuit – Schematic created using CircuitLab Note that the photodiode is reverse biased through the 1 Meg resistor R1. The photocurrent generated by the diode opposes the flow of leakage current through this reverse biased diode, ...


10

I have never ever noticed that a remote control or any other IR-LED emits any red light. It might glow very, very dark, because a tiny little bit of the light is emitted at higher, visible wavelengths. Maybe, you are a bit special and can see light deeper into the IR range, that would be interesting. On the other side, you ask why do most tv remote ...


10

Yes, it will work. Look at the sensitivity/emission vs wavelength curves. It is a spread and there is a point of overlap where both devices have reasonably high values.


9

A diffuser (e.g., a piece of frosted glass) can be used to scatter light from a large target area toward a sensor mounted some distance behind it. You'll need to do the calculation (or experiment) to determine whether enough light reaches the sensor from all points on the target area, and with different incoming light angles. As far as detecting multiple ...


8

Idea 3: Use a camera. I don't know what constraints you have on your object, but if you can add a tiny LED, then tracking with a camera can be a doddle. Jennifer here is sporting a range of red LED trackers. Perfect for bedazzling and confusing your friends. Synchronise the LED to flash in time with the camera's frame rate, so that you get one image with ...


8

I'm taking the liberty of answering my own question as I got most of it figured out and this is a good way to share my findings. My thanks to Olin Lathrop for giving me a place to start and some ideas to try out, but ultimately, the protocol turned out quite different from Olin's guess, hence me posting this answer. Update: I posted a follow-up question ...


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