"High" is half a volt?

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I've been using some TSOP2438 infrared receivers to detect trains and the like blocking flashing IR LEDs for quite a while now, but I've been stuck for several days on a project with 3 of them. They're stuck in my breadboard with an arduino and a bunch of wires.

 

They detect the IR LED just fine. I have the LED flash at 38KHz for 1mS then turn it off for 3mS. The problem is, these 3 only give me a high of about half a volt, way too low for the arduino to detect as a high. I can see the expected waveform. First thought was I had the arduino pin misconfigured, but if I disconnect the output pin from the arduino, the signal stays the same. Power? Nice steady 4.38v, well within the range for the part. The datasheet for the TSOP2438 shows an NPN output transistor and a 33k pullup inside the pack. I've tried it with an external pullup but still get the same low waveform.

 

 

Ok. Maybe the high is .6v, but I'm still mystified. The blue trace is the VCC supply. The yellow trace is the unloaded output. You can see a little noise on the VCC as the IR LED is flashing.

 

 

Ideas?

 

(Sorry, toes don't show in either photo, but they are indeed bare.)

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The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

Last Edited: Wed. Feb 22, 2017 - 06:21 PM
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Are you talking about the 3 legged device? I see a Green, a Yellow and a Brown wire connected to that but I don't know which wire is which.

 

Do you have a datasheet for it? (ie is it connectd correctly?)

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Does it require a pull-up resistor? What happens if you add one, just as an experiment?

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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He did try a pull up, my concern was that it is wrongly connected (don't ask why I suspect this....)

 

They seem to have a standardised pinout with GND on the centre pin (2) and output on pin 1, I guess the Brown wire, which seems to be connected to the LED also and therefore suspicious.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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In my experience, when debugging seemingly simple stuff like this the first thing to do is to clean up your own mess.

In your case this probably means:

Use the "bus bars" on the breadboard for power supply.

Always connect Vcc / GND of components directly to the "bus bars". (So it's easy to optically verify which are the power lines).

Put in some decoupling caps directly on the bus bars and/or directly over the IC's.

Remove unneeded wires or rebuild a part on a separate (part of) the breadboard.

For example. Sensor seems to be in "32", "33", "34", but there is a single wire going to "35". What's that for? Is that supposed to be Vcc? (Again, use the "bus bars").

Is the GND of the scope the same as the GND of your breadboard?

 

 

And it's often in the silly compartment. Broken wires, bad contacts on BB, bad batch of sensors, sensor swapped 180 degree but that all seens to obvious.

Connect the scope to Vcc of the sensor. It could be that the source impedance is to high z(bad contact) and your NPN transistor (with 33k) shorts Vcc to gnd.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

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Can you post a schematic of whats on the BB?

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Who else thinks the 0.6V looks suspiciously like a diode drop ?

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or perhaps a 10x probe :)

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Hmm. Rebuilding the circuit.

 

Oddly, these have the + in the middle and - on one side:

 

 

Was surprised to get ALMOST the expected output. The puzzle, of course, is these are familiar parts I've used before, in fact, right on this same breadboard with a similar circuit just a few days ago.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

Last Edited: Tue. Feb 21, 2017 - 05:03 PM
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these have the + in the middle and - on one side:

Maybe you have one with the "standard" pinout like the TSOP44 (top line)?? They seem to be Vishay brand.
 

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

This reply has been marked as the solution. 
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I have ground and output swapped. I wired it as if it's facing me, but it points the other direction.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

Last Edited: Tue. Feb 21, 2017 - 07:57 PM
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Put a boot on the right foot and step one the toes of the left foot now......

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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For Torby, just putting the boot on would be punishment enough!

 

JC

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Torby wrote:
I have ground and output swapped. I wired it as if it's facing me, but it points the other direction.

Ah Ha! That explains the diode drop then.

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What I find surprising is the miswired device was nearly working.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

Last Edited: Wed. Feb 22, 2017 - 03:28 PM
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Bet SOME of you thought I didn't even HAVE boots:D

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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It's amazing what one can do with Photoshop these days ;-)

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joeymorin wrote:
It's amazing what one can do with Photoshop these days ;-)
  ROFLOL

+1yes

David (aka frog_jr)

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joeymorin wrote:

It's amazing what one can do with Photoshop these days ;-)

 

hehe

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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It's not even photoshopped, that's just someone else's boot.  Maybe a dual boot?

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No its definitely only a single boot

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Ok, I believe it is time to reboot this thread...

David (aka frog_jr)