Basic 38kHz detector

Reloadron said:

I agree that all he cares about is that it sees something or not and as long as a pulse(s) manage a trigger that could be latched for a moment using maybe a 555 as a one shot it could likely work. I just didn't know for sure it would do as he wants so I didn't suggest it or attempt a circuit for it.

Ron

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As it so often happens, the OP stopped posting, leaving us to debate what he wanted amongst ourselves. :^) I realize the method of just detecting pusles might be crude, but it would allow one to easily repurpose a common household object, as I'm sure we all have a drawer full of them.

hi all, i'm the original OP, for some reason i stopped getting email alerts for replies to the topic.

anyway, yes, all i really want to do is trigger a relay. my old camera had an IR receiver built in, and so i have a little remote to trigger it. the new camera i bought does not have an IR receiver, but does have an input plug on it where, when a circuit is completed over it (hence the relay) the camera takes the shot.

so, in all actually, it want to use this same remote, to power a relay, which will complete an arbitrary circuit. i do not want to decode the IR signal or anything. like someone else said: IR pulse present -> trigger. the whole interface between said circuit and camera i have taken care of from my side, all i need help with is the IR communication with the relay.

is that clear? where do i go from here?

There is IR in sunlight.

If a car turns, and reflects, "snap"

False triggers are a reason for coding and de-coding.

Here's one project for IR decoding using a small PIC, source code, schematics and PCB layout.

RMMM said:

There is IR in sunlight.

If a car turns, and reflects, "snap"

False triggers are a reason for coding and de-coding.

Click to expand...

I'll only be using it indoors...

titous said:

I'll only be using it indoors...

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Still need a decoder of some sort.

am i right in my understanding of how the IR rx works in that, if it's hooked up to a 5V source, when it detects no IR signal, the output voltage is 0V and when it does detect a signal the output source is something other than 5V?

would it be simpler to do RF?

No IR signal would be at some low level, and a detected level would be at a higher level ( not strictly at 0V and 5V ). The trick would be to set the detector to trigger on the higher level. This could be done with a comparator circuit fed by a detector/amplifier. But you need some idea of what those levels are first. Experimentation with your remote and a detector would be the best way to ascertain the data. Once you have that, it would be pretty simple to design a detector.

Flash

Maybe I'm missing something but this is what I think you want.

Most detectors are active low, meaning when they get a signal they go from +5 to 0 volts. If I understand you right you want to click a key on the remote (any key will do) and have the flash trigger. If so, the circuit below should work. It should be a small relay - I think radio shack has 5 volt reed relays so the ic can drive it. The series of pulses from the remote triggers the one shot which closes the relay, flashing the camera. The trace on top is the output of the one shot (about 1/3 of a second) to simulate the button push on the camera.

I forgot we're talking about a receiver, and not just a sensor, in which case, you should get full digital output levels.

titous said:

I'll only be using it indoors...

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I've done something like this before by making my own "infrared remote" and a 393 comparator with an infrared detector LED. Instead of using a remote with pulsed IR, just have an IR LED connected with a push-button switch. The comparator is connected to the IR detector, and a variable resistor is used to adjust the sensitivity. You can turn the VR until the output just goes off, and when the detector senses the IR light, the voltage increases and the 393 turns on the output (to the relay). I admit, this design is very crude, but it may still be able to do what you want it to do. I can try to post a schematic if you need one.
Good luck!
Der Strom

ronv said:

Maybe I'm missing something but this is what I think you want.

Most detectors are active low, meaning when they get a signal they go from +5 to 0 volts. If I understand you right you want to click a key on the remote (any key will do) and have the flash trigger. If so, the circuit below should work. It should be a small relay - I think radio shack has 5 volt reed relays so the ic can drive it. The series of pulses from the remote triggers the one shot which closes the relay, flashing the camera. The trace on top is the output of the one shot (about 1/3 of a second) to simulate the button push on the camera.

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i seem to be getting a lot of contradictory replies (thank you for all of them!) but this seems promising. i'm a bit confused about attaching the detector though, mine has three leads (+5V, ground, and signal) yet the diagram only shows one. also, is the shape at the very top middle with the +5, does that mean the input voltage +5V?

thank you very much!

DerStrom8 said:

I've done something like this before by making my own "infrared remote" and a 393 comparator with an infrared detector LED. Instead of using a remote with pulsed IR, just have an IR LED connected with a push-button switch. The comparator is connected to the IR detector, and a variable resistor is used to adjust the sensitivity. You can turn the VR until the output just goes off, and when the detector senses the IR light, the voltage increases and the 393 turns on the output (to the relay). I admit, this design is very crude, but it may still be able to do what you want it to do. I can try to post a schematic if you need one.
Good luck!
Der Strom

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hi derstorm, yeah that is exactly what i'm looking for, i'd love to see a schematic!

Go to this link. Scroll about 2/3 the way down. You'll find a schematic for a receiver that should get you started.

titous said:

hi derstorm, yeah that is exactly what i'm looking for, i'd love to see a schematic!

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Ok. I don't have the exact schematic right now, but I can try to post the circuit sometime this afternoon. My computer has been a little screwy, lately, so I hope it will let me do this . Sorry for making you wait :/
Der Strom

The datasheet from the manufacturer of the IR receiver you have shows its pins on a photo, how to connect it and its details.
But if you bought it at a ripoff price from RadioShack then even they don't know anything about it and don't even know who made it.

titous said:

i seem to be getting a lot of contradictory replies (thank you for all of them!) but this seems promising. i'm a bit confused about attaching the detector though, mine has three leads (+5V, ground, and signal) yet the diagram only shows one. also, is the shape at the very top middle with the +5, does that mean the input voltage +5V?

thank you very much!

Click to expand...

I just drew the output of your detector. You still need your 5 volt regulator and voltage and ground to your sensor. Keep in mind your sensor may be bad now if you hooked it to 9 volts. The +5 in the center of the schematic is power from your 5 volt regulator to power the IC.
Here is a spec sheet on how these sensors work. They have several advantages over just a photo diode in that they reject ambient light, and have automatic gain control which gives them their range.

https://www.electro-tech-online.com/custompdfs/2010/12/TSOP4840.pdf
You might want to add the little filter (100 ohm and .1 ufd. cap) to your sensor. (Page 1 app circuit)
Page 2 shows the active low output.

I apologize, I can't seem to find the actual schematic, but I have the one my circuit was based on:

View attachment 393_light_sensor.sch

You can probably find a way to switch out the CdS photocell with an IR phototransistor, and the part that says "to relay" should probably actually attach to a 555 timer wired in bistable mode (to switch the relay more easily). This way, when the phototransistor receives a signal of IR light from your handheld remote (described in a previous post), the output of the 393 goes high, which triggers the 555. To do this, simply connect an NPN transistor to the 555 (collector to pin 2, emitter to ground, and the base to the output of the 393). The 555 can then switch the relay by using a transistor, and the output of the 555 stays high for a certain amount of time before switching off.
Let me know if you have any more questions, and I'll try to answer them.
Good luck!
Der Strom

note: keep in mind that the output from an ordinary IR LED generally is not enough to be sensed by the 393, as the voltages compared by the chip must have a significant difference. You may want to find a higher-quality chip that can act as a comparator, and is able to measure and compare similar voltages. You may also want to use some kind of reflectors/lenses to direct the IR beam.

If you do not already have the ExpressSCH program on your computer, you will probably have to download it before opening the schematic. Sorry about this inconvenience
Der Strom

thank you everybody for your great help, it's people like you that help people like me get their little projects off the ground. at this point i'm going to take ronv's advice and build the suggest schematic, if that doesn't work, i'll fall back on the other ideas proposed, namely DerStrom! i'll post back with what i found to resolve the problem soon i hope