Problem with IR receiver module and IR LED

[Liamlambchop]

Hello all,

I have a Vishay TSOP34138 IR receiver module. It's carrier frequency is 38Khz. I have it connected to 5Vs and am getting a current flow (from the Vs to the ground) through the device when there is no IR present. This is a problem.
The diagram, labelled 'block diagram', on the first page of the module's data sheet (https://www.newark.com/pdfs/datasheets/vishay/TSOP34.pdf), shows that when the base of the transistor in the receiver module isn't activated there should be no current flow. Considering that I'm getting current flow I am assuming that my base is activated. But it shouldn't be, because my IR receiver module should only respond to 38KHz radiation.... and I'm not producing any of that.
I don't understand how this is happening........

I have this receiver module so I can use it as a sensor for an IR LED (data sheet: https://www.farnell.com/datasheets/391119.pdf) in a break beam counter. I am using an Arduino to make the IR LED blink at 38KHz . (NOTE: the problem described above still occurs when my IR LED is not plugged in.

Also, what sort of output will my receiver module have? I know that the info is in the data sheet, but I am not familiar with all of the jargon yet. What i'd like to know is: What is the max output voltage of the receiver, and is this large enough for a data logger to recognise it as a digital high?

Any help would be greatly appreciated

Thank you,
Liam

 

[BradtheRad]

1.

The datasheet states 1.2 mA as typical constant current draw. A little more in sunlight. Max is 1.5 mA. Are you drawing more than that? If so then the device may be ruined.

2.

The block diagram shows that a transistor pulls the output pin to ground. This means it sinks current from your external circuitry.

According to the specs, the device pulls output low when active. Down to 250 mV.

An internal pullup resistor is there to provide a high signal. It will supply .17 mA through the 30k resistor (if your supply is 5V).

3.

The output transistor could be ruined if you applied overmuch voltage or current at the output pin.

You will have to test the device in all conditions of light and dark, with and without 38khz IR flashes, to find out if you can still make it work for you.

If the output no longer swings to the extremes it's supposed to, you can still add a pulse-conditioning circuit.

4.

A caption states your external circuit should not continuously pull the output low. The specs mention output V in more than one place. Apparently as to what V level you should expect under which conditions, and what V is safe to apply to the output pin under which conditions.

The specs give max output current as 10 mA. I think this means you must not send more than 10 mA INTO the output. As a precaution I would attach a 500 ohm resistor to the output pin. ( 5V divided by .01 A).

 

[Liamlambchop]

Mate! Thank you I think I would have buggered my module because, like the noob I am, attached the Vs pin directly to 5Vs. That mean that it had no protection. I needed to put in a 33k res. on the ground pin right?

The specs give max output current as 10 mA. I think this means you must not send more than 10 mA INTO the output. As a precaution I would attach a 500 ohm resistor to the output pin. ( 5V divided by .01 A).

Do you suggest this just in case, somehow, 10mA gets sent the wrong way into the output pin? Because the current going into the module is only 1.5mA, so I don't see how 10mA could be outputted with no external voltage applied....

As far as the functioning of the device goes: does the current travel from Vs, through the control circuit, through the base of the transistor, through the emitter of the transistor, then to ground when there is no 38kHz infrared shining on it? And what about when there is 38kHz IR? and.... does any current travel to ground via the 30k resistor, then through the transistor?

Cheers for your help, it was really really..... helpful

 

[BradtheRad]

Mate! Thank you I think I would have buggered my module because, like the noob I am, attached the Vs pin directly to 5Vs. That mean that it had no protection. I needed to put in a 33k res. on the ground pin right?

It should not hurt to hook the supply pins directly to your supply.

However it would be wise to do as the datasheet depicts, namely to install a 4.7 uF capacitor across pins 3 & 2, then insert a 100 ohm resistor inline with the supply. This reduces voltage spikes at the supply pins.

I wrote:

The specs give max output current as 10 mA. I think this means you must not send more than 10 mA INTO the output. As a precaution I would attach a 500 ohm resistor to the output pin. ( 5V divided by .01 A).

Do you suggest this just in case, somehow, 10mA gets sent the wrong way into the output pin? Because the current going into the module is only 1.5mA, so I don't see how 10mA could be outputted with no external voltage applied....

Right. If the transistor is conducting, and positive voltage is applied inadvertently to the output pin, you could fry the transistor.

We can't be absolutely sure that would happen. It's not stated whether the transistor only turns on enough to permit a maximum of 10mA per the specs chart. Anyway it's better to be safe than sorry.

As far as the functioning of the device goes: does the current travel from Vs, through the control circuit, through the base of the transistor, through the emitter of the transistor, then to ground when there is no 38kHz infrared shining on it? And what about when there is 38kHz IR? and.... does any current travel to ground via the 30k resistor, then through the transistor?

The datasheet says 'output active low'. This means the control circuit detects 38kHz and sends current to the base of the transistor. The transistor turns on and conducts from the 30k resistor to ground. At the same time this provides the output pin a low ohm path to ground. The transistor is said to pull the output pin low. It can sink current. An LED will light up if you connect it to the output and supply pins (add a limiting resistor).

Other times the transistor is off. Current can come through the internal 30k resistor to the output pin. In other words it can source about .17 mA. This is barely sufficient to light up an LED connected to the output and ground pins.

It may seem counter-intuitive to do it this way. It has an advantage because components will give you some kind of reading in idle mode, when you check connections, troubleshoot, etc.

 

[Liamlambchop]

Thanks mate, that's great

Still one question.....

It should not hurt to hook the supply pins directly to your supply.

How do we ensure then that the supply current doesn't exceed 1.5mA?

Thanks mate.

 

[BradtheRad]

How do we ensure then that the supply current doesn't exceed 1.5mA?

The internal circuitry has an impedance of its own. Most of the time you need not install any components in the supply leads.

Sometimes specs call for an extra bit of filtering or isolation. That would account for the 4.7uF cap and the 100 ohm resistor shown in the spec sheet.

Furthermore in case the device were to short circuit internally, the 100 ohm resistor will let no more than 50 mA go through.

 

[Liamlambchop]

Thanks for all your help Brad!
I have definitely progressed a lot since you started helping

 

[Liamlambchop]

Hey guys,

Haven't been on this thread for a while, but I've come up against another problem.

My TSOP34138 ir receiver module acts strangely.... I can have it facing an ir transmitter, emitting 38kHz ir, and it won't output a LOW, and when I move my hand in front of the transmitter (as if to block the transmission and cause a reaction from the TSOP34138) nothing happens, the TSOP continues to output a HIGH. But, when I cover the TSOP with my thumb for a number a seconds then remove it all of a sudden it starts responding to the ir transmitter - it will output a LOW when it detects 38kHz ir, and a HIGH when I block this ir. Why is this?

I have hypothesized that my TSOP is the wrong type of ir receiver module for my 'break-beam people counter' application, because it is designed as a TV remote control receiver (where it is waiting for the occasional burst of 38kHz ir). My application is the opposite in a way, because it is CONSTANTLY receiving 38kHz ir and is waiting for the occasional break in the ir beam. In the TSOP data sheet (attached) it says on the first page, under Application Circuit, that the output voltage shouldn't be kept under 2V by the external circuit. In my application the constant 38kHz ir is keeping the output voltage under 2V, is this doing exactly what the data sheet is telling me not to do?

If I am using the wrong receiver, then why, in this tutorial I found for a break beam counter, is it recommending the same TSOP receiver?

Cheers for your help.