IR Switch

  • Thread starter jbord39
  • Start date
  • #26
vk6kro
Science Advisor
4,081
40
I think 38 KHz receivers have to have a resistive load on them. Does yours have a resistor going from the output to the 5 Volt + power source?

I have seen the sensitivity curve of these receivers and it is usually bell-shaped with quite a broad peak in the centre. So, it would probably work between 37 KHz and 40 KHz and be less sensitive if you moved outside those frequencies.

Have you got a data sheet for your receiver? You can find them on Google.

They are amazingly sensitive. I used one and it would even detect signals reflected off the walls.
 
  • #27
74
0
Hm. I don't think the diode is getting the required voltage to turn on. I can't see anything on my digital camera (unless you need a special setting?). Before I unsolder the 5V regulator to apply a higher voltage, I was wondering if that would work. The IR diode has a forward voltage of 1.28 with 100 mA.

Thanks,

John
 
  • #28
74
0
I can see the IR transmitter with my digital camera, I just had to put it on night mode.

It's strange, but I can't seem to get ANY change in signal out of my 38kHz IR receiver; even using the exact circuit you drew (with my transmitter and with a remote).

I also don't really understand why the resistor is connected between the input and output (wouldn't that cause current to flow even with the IR receiver is not receiving?).

Thanks again,

John
 
  • #29
vk6kro
Science Advisor
4,081
40
Do you have a data sheet for your IR receiver chip?

The connections may be different to the one I showed.

The output can be an open collector. This means the transistor at the output of the chip can be switching, but it needs a load resistor to work. It would only carry current if the transistor was turned on.

Some TVs have a light that comes on when you use the remote control. This could be used to get your transmitter on frequency.
One problem with using a multimeter to measure frequency is that they have long unshielded wire leads that can pick up all sorts of interference. This is why you are getting the random readings you mentioned earlier.
 
  • #30
74
0
Is there any way to increase the voltage of the output pulses? Compared with another remote side by side it is only about half as bright (using digital camera).

I managed to use the remote to light an LED using this circuit:

[PLAIN]http://www.reconnsworld.com/ir_ultrasonic/40khzirtest.gif[\IMG][/URL] [Broken]

I tried connecting the base of an NPN transistor where the LED is, with the emitter where the LED connects to the IR receiver. I then connected a motor with the top connected to a 9V battery to the collector of the NPN. My hope was that a small current into the base would allow current to flow through the motor.

Any help is appreciated.

Thanks.
 
Last edited by a moderator:
  • #31
vk6kro
Science Advisor
4,081
40
You can increase the LED current by increasing the voltage on the TLC555 or by reducing the size of the resistor in series with the LED.
The voltage can be up to 15 volts but the output current should not be more than 10 mA, according to the data sheet.

So, you would need to use a transistor to drive the transmit LED, like this:
http://dl.dropbox.com/u/4222062/LED%20driver%202.jpg [Broken]
That 20 K resistor can be made lower if you want more LED current.

I modified your diagram to give a couple of drive circuits for your 38 KHz receiver.
Glad you got that working.
Both circuits turn on the relay when a signal is received.

Depending on your motor and what types of relay you can get, the first circuit may be adequate or you may need to use the second circuit.

I favour using a relay to drive the motor. Motors can draw a lot of current if they stall and this might damage the drive transistor.

http://dl.dropbox.com/u/4222062/38%20KHz%20receive.PNG [Broken]
 
Last edited by a moderator:
  • #32
74
0
Thanks for the help. I'll build and test the circuits out over the weekend and hopefully have this finished within the week :)

edit: So many PNP transistors. Why are they better to use than NPN?
 
Last edited:
  • #33
74
0
Would this design work to increase the output from an LED? The one above doesn't seem to amplify it to it's maximum light output (as compared side by side to the same diode with 60 mA of current through it).

Do you think this would amplify the current up to high brightness?
Feeding the output pulse into the body of an NPN transistor, with the collector connected to +5V, with the emitter connected to the body of another NPN transistor (with it's collector connected to +5V) with it's emitter connected to the IR diode then connected to ground.

edit (Possibly the transistor I am using could be wrong? Switching NPN transistors, bought in bulk from radioshack).
 
  • #34
74
0
The first circuit (with the PNP transistor) doesn't make sense to me. The base is connected to the output of the 38 kHz receiver. This output (when it receives 38 kHz IR light) is 0 V. This would case the base and the emitter to be effectively grounded, and the transistor could not send any current (the pn junction would be at 0V -> no current flow).

Am I thinking of this wrong?

Thanks again,

John
 
  • #35
vk6kro
Science Advisor
4,081
40
The first circuit (with the PNP transistor) doesn't make sense to me. The base is connected to the output of the 38 kHz receiver. This output (when it receives 38 kHz IR light) is 0 V. This would case the base and the emitter to be effectively grounded, and the transistor could not send any current (the pn junction would be at 0V -> no current flow).

Am I thinking of this wrong?

Yes.

The emitter of the PNP transistor is at +6 volts. For the PNP transistor to turn on, it has to have less than + 5.4 volts on the base.
This happens when the output of the receive chip goes to zero volts.


This circuit works better for the transmitter:
http://dl.dropbox.com/u/4222062/Darlington%20LED%20driver.PNG [Broken]

If your 80 mA is correct and it is average current, this circuit should be OK.
The calculated current here is about 85 mA, but the LED is not lit all the time.
So you could try this, keeping a watch on it with your digital camera.
This is really pushing the LED. Never push a normal LED like this.

You could possibly start the LED series resistor as 100 ohms and drop it in steps to 82, 68, 56 ohms etc.
If you compare it with your TV remote, you might be close.

Be careful. LEDs fail if you put too much current through them. The actual current will depend on the supply voltage, too, so if you have more than 6 volts the series resistor will have to be larger.
 
Last edited by a moderator:
  • #36
74
0
Thanks for the reply. I'll work on the circuits and get back :)
 
  • #37
74
0
Here is the finished schematic for the controller with pictures. Thanks for the help everyone...
Now to make the car.
Toyschematic.png


DSCF0556.jpg


DSCF0557.jpg
 
  • #38
I also am interested in this circuit,I am basically doing the same thing,but my beam is a shorter distance( 10 - 12 ") and will be operating a small dc motor( 1.5- 9vdc) so this circuit has capability to run motor without a relay?
 
  • #39
685
16
Hi jbord39,
In your latest circuit, the Green Led can never be ON.
Also, if Your 555 can work with 9V, why use 7805. It will continuously drain current from the battery. You could just eliminate it, and use 9V instead.

You haven't shown any resistors in the Left sides of the 555. You would need one to the Base of first transistor and in series to collector of second transistor. Otherwise, too high currents will flow, not good for Leds.
If you have already used this circuit then the IR LEDs are already damaged or atleast <what I would like to call> abused.
It means, they aren't dead, but they produce too little light from too high current.
Try using fresh Leds and use resisters always.
 
  • #40
vk6kro
Science Advisor
4,081
40
Jbord39 hasn't been around for about a year.

This thread is from 2 years ago and the last circuit does have errors in it.

This is unfortunate as it has had a lot of viewings.

thebeaverwhis:
The circuit was intended to drive a LED on an infra red transmitter, but it might be OK for a motor if the transistors could carry enough current.

However, a motor can draw a lot of current if it is stalled and this could easily destroy a transistor if it wasn't big enough to cope with the current. So, you would be safer using a relay to switch a motor.

You may need to hunt around for a complete circuit for a transmitter and a receiver and a motor driver if you want to make up a complete setup.
Post #5 above gives part of a complete transmit / receive setup.

If your distances are small, you might be able to use a simpler transmitter and a infra-red phototransistor as the receiver.
 
  • #41
685
16
Jbord39 hasn't been around for about a year.

This thread is from 2 years ago and the last circuit does have errors in it.

Too bad that I never check dates.
 
  • #42
74
0
Too bad that I never check dates.

I am back!

About the mistakes in the circuit, I had just started designing electronics (I had just started college).

The green LED should be connected to 5V instead of ground on one end.

Also the reason for 5V as opposed to 9V is to prevent changes in the circuit functioning (like oscillation frequency) when the battery voltage drops. It provides a voltage supply 'buffer' of sorts.

And the diodes should have a current limiting resistor. I tried a million times and something is wonderfully broken because with a resistor I can't get 100 mA in each diode. They are abused perhaps but still working just as well (the sender will bounce around a wall before losing power to the receiver).

I will post a receiver circuit soon.
 
  • #43
74
0
Hey an updated (an better) schematic is in the attachments. The tuning pot is used to make sure the output is right around 38kHz. The receiver (output is HIGH with no input and LOW whenever it receives 38kHz, from Radioshack) is hooked up to a 555 timer in monostable mode (this produces a single long output whenever its trigger goes LOW). The output is To BeagleBoard.

Currently the monostable 555 produces an output that is about 1-2 seconds long. If you are running something and need it to stay on for like an hour or more you could change that. You could also modify the monostable 555 to make it more like a flip/flop.

The main problem I had with this circuit is that the device you are turning on needs a constant supply of power just to monitor if it is going to be turned on or off. So for a receiver something plugged into the wall works best as opposed to battery powered.
 

Attachments

  • sensor.png
    sensor.png
    17.8 KB · Views: 409

Related Threads on IR Switch

  • Last Post
Replies
5
Views
3K
Replies
10
Views
17K
Replies
2
Views
3K
  • Last Post
Replies
2
Views
6K
  • Last Post
Replies
4
Views
6K
  • Last Post
Replies
8
Views
3K
Replies
3
Views
4K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
9
Views
3K
  • Last Post
Replies
12
Views
7K
Top