Basic 38kHz detector

[titous]

Hello everyone! I've got a DIY home project that I need help with; my background is mechanical engineering, and I've only had one circuits class several years ago, so bear with me.

I'm trying to build a circuit which will operate a relay and thus complete a circuit, and I'd like to be able to operate it with an IR remote (basically I'm making an IR camera trigger to be used for photography).

I'm taking it one step at a time and first I'd like to get the actual detecting part down by testing it with a generic TV remote which I'm assuming is sending a signal at 38kHz. I bought a 38kHz IR receiver module form radio shack (276-640) and have attached it to a bread board to see if I can read the signal sent from the remote.
**broken link removed**

The part on the left is my way of sending a +4.5V to the receiver as well as making a "virtual ground". The square object on the right is the actual receiver (couldn't find the symbol for it).

When I have it all hooked up, and I try to read the signal (by attaching a volt meter across the signal out and ground) I'm getting a stead signal of about +2V and when i press the remote button, I see it dip slightly. I expected to see a +4.5V whenever the receiver sees the IR signal, can anyone tell me what I'm doing wrong?

Thank you all for your help!

 

[MikeMl]

Using a high-impedance voltage divider to reduce a power supply will not work. You have created a 4.5V source, but it has a 5K effective source resistance, which is too high. Either use a 5V supply, or an IC regulator (7805 type) to reduce 9V to 5V. AFICR, the output pin on the IR rx requires an external pull-up resistor to +5V.

There have lots of posts on these forums about using IR remote control receivers as "beam break" detectors. Use Google Advanced search restricted only to the https://www.electro-tech-online.com domain to find them. I have posted some of them.

 

[titous]

Hi Mike, thanks for your input.

I did an advanced search on the forum and didn't find anything satisfactory, so I've got a few new questions:
- can i hook up a resistor, say 47k, to the 9V battery source to bring it down to ~5V?
- what is an external pull-up resistor and how to i use it on the IR rx?

thanks for your help!

 

[Reloadron]

OK, what Mike is telling you with this:

You have created a 4.5V source, but it has a 5K effective source resistance, which is too high.

is that although using two 10K resistors in series with a 9 volt source looks like it will give you 4.5 volts out, in reality it won't because you have your load across one of your divider resistors so it is no longer 10 K ohms but something considerably less. Won't work.

Since you mentioned Radio Shack I would suggest you go back there and buy a LM7805 voltage regulator chip for literally a few bucks. That is a 5 volt regulator single 3 lead chip. Input, Output and Ground. That will get you 5 volts.

As to the pull up you mention I am not familiar with the spec sheet for your module but I would try maybe a 10 K resistor between the module output and your +5 volt supply.

Ron

 

[titous]

Since you mentioned Radio Shack I would suggest you go back there and buy a LM7805 voltage regulator chip for literally a few bucks. That is a 5 volt regulator single 3 lead chip. Input, Output and Ground. That will get you 5 volts.

Thanks for getting back to me Ron. Would simply putting a resister in series with the +9V be another option (one i can do now since i have a bunch of resistors) or is the voltage regulator chip really the best way to go?

 

[Reloadron]

Voltage regulator chip, believe me.

Short of explaining why the resistor won't work in detail it just can't be used to get where you want to go.

Ron

 

[titous]

Voltage regulator chip, believe me.

Short of explaining why the resistor won't work in detail it just can't be used to get where you want to go.

Ron

Ron, I've taken your word for it and have updated my circuit to the following:
**broken link removed**

I am getting the +5V into the IR rx; however when I read the output under no signal I'm getting about 4.5V and when I do send a signal I get about 4V. Am I doing anything wrong? Also, do I understand the behavior of the IR rx correctly in that under no signal it should show 0V and that when it does read a signal it should show 5V?

 

[MikeMl]

The IR receiver is designed to detect an IR beam that is a complex series of on-off keyed pulses with a specified timing. It is not really designed to just detect the presence/absence of an IR beam. If you aim a TV remote at it, the output pin should pulse, but at a rate too fast for a DVM to follow. If you observed the output using an oscilloscope, you would see a complex series of pulses.

 

[titous]

The IR receiver is designed to detect an IR beam that is a complex series of on-off keyed pulses with a specified timing. It is not really designed to just detect the presence/absence of an IR beam. If you aim a TV remote at it, the output pin should pulse, but at a rate too fast for a DVM to follow. If you observed the output using an oscilloscope, you would see a complex series of pulses.

could you then point me in the right direction or suggest to me how i can power a 5V relay to function with an IR remote?

 

[MikeMl]

could you then point me in the right direction or suggest to me how i can power a 5V relay to function with an IR remote?

You would have to decode the complex series of pulses as discussed here and here.

 

[blueroomelectronics]

You also need some extra power decoupling for most IR detectors. My Junebug has a schematic that shows a typical setup with a microcontroller.

 

[RMMM]

My Februarybug has it too.

 

[blueroomelectronics]

A Junebug kit.
**broken link removed**

 

[BrownOut]

You would have to decode the complex series of pulses as discussed here and here.

Are you saying he can't just detect the presence/absence of a pulse train. I'm not buying that. He should be able to detect/rectify/filter/amplify the pulses to operate his relay.

I'm not saying it won't be tricky.

 

[MikeMl]

Are you saying he can't just detect the presence/absence of a pulse train. I'm not buying that. He should be able to detect/rectify/filter/amplify the pulses to operate his relay.

I'm not saying it won't be tricky.

The way I read the OP's requirement is that he wants to control something using a TV remote. That implies decoding at least two buttons.

 

[BrownOut]

The way I read the OP's requirement is that he wants to control something using a TV remote. That implies decoding at least two buttons.

I see. I thought he just wanted ON/OFF programmability. I admit I dont' always read the entire threads or posts.

 

[Reloadron]

This is why using a setup like this can get complex for an IR Remote to just trigger a camera. Most camera manufacturers do make auto remote trigger systems for a reasonable price. Another good way to go is using an RF remote.

@ MikeMl, wasn't it a few weeks ago I think it was you who posted a nice little two channel relay board with a remote key fob transmitter for about $30 USD? I can't recall the details but it looked to be a nice price. The little relay board could be set for pulse or latch action. The ones I am familiar with are 4 channel and cost more than they are worth for this application.

Now as Mike points out you would need to decode the pulses or build your own transmitter which makes things more complex.

You just want to trigger a camera shutter remotely?

Ron

 

[BrownOut]

Still don't see what it should be so complex if one only want to trigger a shutter??? No pulses, no trigger. Pulses present -- trigger. What am I missing?

 

[blueroomelectronics]

IR remotes send a digital data stream. There are many flavors but you need to decode it. Google SIRCs for an example of the Sony protocol.

 

[Reloadron]

Still don't see what it should be so complex if one only want to trigger a shutter??? No pulses, no trigger. Pulses present -- trigger. What am I missing?

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