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Motion Alarm Help

Alex Scott

Jul 3, 2014
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Hey guys, so I've got this kit as i'm new to the world of electronics and plan to learn, so I have these DIY kits that provide you with the components and a PCB and you solder it all yourself, I have made plenty of these successfully, my soldering technique is fine, all the solder joints appear to be fine however i'm having an issue.

There are 2 PCB's to this project, one transmitter and receiver. Both have LEDs on the end and when that path is blocked, a sound/alarm is made through a speaker.

Now everything appears to be fine except when I turn the PCB with the speaker on, it just constantly makes the noise. Now I know both parts are working, when I place the transmitter infront of the receiver, the frequency slightly changes so the 2 units are definitely registering that the other unit is there and everything appears to be working fine and the LED's are "seeing" each other. I have plenty of tools and a multimeter to test things, where would I begin testing what is wrong here?

This is a link to the unit in question, I have attached 2 photos of my completed boards. Thoughts on any of this?

http://www.velleman.co.uk/contents/en-uk/p46.html
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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If you put them really close together, does it work?

Can you confirm (with the aid of your mobile phone camera) that the LEDs in the transmitter light up? Your mobile phone camera will probably detect the glow from the IR LEDs.

How does the sound change when you bring the light source into alignment with the sensor?

Can you post a component overlay of both of these boards (but especially the receiver)? A circuit diagram would be good too.

This is what's on the web site and is clearly insufficient. And it's even worse that the put the component designation UNDER the component! Aaaagh!
 

Alex Scott

Jul 3, 2014
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Using an iPhone 4S the only LED that shows up is the LED on the receiver that's not phototransistor LED as described, just a normal LED. I can't see any of the other LED's working using my phones camera, they are described as phototranistor LEDs, do these work the same way as infrareds?

I'm afraid I don't have a component overlay or circuit diagram, all I have is that link you showed me. It's quite easy to follow and I have followed several before it all 100% successfully. The sound changes quite dramatically, if the receiver (the unit with the speaker) is turned on without the transmitter, the sound is very high pitched and incredibly painful to listen to. When the transmitter is turned on and placed infront of it the sound is a fair bit deeper, a much lower frequency and will vary slightly up and down if you move around the transmitter.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Really!?!? Is that *all* they give you?

Obviously they don't want you to learn anything or be able to troubleshoot the problem.

I suspect that you've either got a component misplaced, or you have bridged a connection.

Can you annotate your image with the component designations (R1, R2, D1, C1, etc) so I can check everything's in the right place, and can you show me the underside of the receiver.

I'm surprised that the transmitter's LEDs don't show up on your phone camera. Can you test it with a TV remote? Can you see the LED on that flash when you press buttons?
 

davenn

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Using an iPhone 4S the only LED that shows up is the LED on the receiver that's not phototransistor LED as described, just a normal LED. I can't see any of the other LED's working using my phones camera, they are described as phototranistor LEDs, do these work the same way as infrareds?

If you cannot see a glow from the 2 LEDs on the transmitter board, then that indicates that they are not operating
and why the receiver piezo is continuously sounding

You could try aiming a TV remote at the receiver and see if that causes the buzzer to stop sounding, that will at least confirm that the receiver is OK

If you cannot see a glow from the 2 LEDs on the transmitter board .... make VERY SURE they are in the circuit the correct way around
They look OK from the dark pic ... just make sure the flat bit near the base rim of the diodes goes to the flat bit as in the PCB printing ( silk screen)

Dave
 
Last edited:

Alex Scott

Jul 3, 2014
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Thanks guys you've all been a big help. I got my iPhone and tested the LEDs on the board and saw nothing, HOWEVER I tested my phone camera with a TV remote that I know works and I couldn't see the LED on that using the camera. I tried a different phone to check there wasn't something wrong with mine and I got the same results.

I'm not at home at the moment, would using a TV remote to trigger the receiver work? If not, what would the next step be?
 

(*steve*)

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I would try pointing the TV remote at it, but it may not do anything (great if it does)

Do you have a multimeter? Reading the Voltage across one of those LEDs could be useful.
 

(*steve*)

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Do you have a multimeter?

Measure the current draw of the transmitter. unsnap one of the battery connections and rotate it away from the battery, then place one meter probe on the free battery terminal and the other on the snap that connects to it. Have the meter in a mA range and the board turned on. What current is reported?

With the battery connected normally and the transmitter turned on, use the multimeter in a voltage mode to measure the voltage across one of the LEDs.
 

davenn

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..................
, would using a TV remote to trigger the receiver work? If not, what would the next step be?

Yup I suggested earlier that you try the TV remote. If your project receiver isn't looking for a specific type of IR signal, them you should get some sort of result :) ( unless you also have a receiver fault .... hopefully not)

and I also suggested to confirm that the 2 transmitter LED's are in the right way around
from the dark pic ... they appear to be ok

cheers
Dave
 

Alex Scott

Jul 3, 2014
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Yup I suggested earlier that you try the TV remote. If your project receiver isn't looking for a specific type of IR signal, them you should get some sort of result :) ( unless you also have a receiver fault .... hopefully not)

and I also suggested to confirm that the 2 transmitter LED's are in the right way around
from the dark pic ... they appear to be ok

cheers
Dave


I tried my TV remote and yes that does affect it to a point. When I switch on the receiver the alarm goes and everytime I press a button using the remote infront of the receiver there is a slight dip in the frequency of the sound. This dip in frequency is made every time I press a button, so the IR's are certainly working?
 

Alex Scott

Jul 3, 2014
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Measure the current draw of the transmitter. unsnap one of the battery connections and rotate it away from the battery, then place one meter probe on the free battery terminal and the other on the snap that connects to it. Have the meter in a mA range and the board turned on. What current is reported?

With the battery connected normally and the transmitter turned on, use the multimeter in a voltage mode to measure the voltage across one of the LEDs.

I'm afraid I don't follow your instructions, most likely due to my lack of knowledge. When you say unsnap, do you mean cut the wire from the battery connector or desolder it from the board, place a probe from the meter on there and then where would I put the other probe?
 

Gryd3

Jun 25, 2014
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I'm afraid I don't follow your instructions, most likely due to my lack of knowledge. When you say unsnap, do you mean cut the wire from the battery connector or desolder it from the board, place a probe from the meter on there and then where would I put the other probe?
I think the assumption is that your kit runs on a 9V battery... the clip can be attached to only one of the terminals and the battery can turn away from the other. This gives you room to put your meter in-between the battery and the rest of the circuit.

If you cannot do this, you may have to, as you said above, desolder one of the wires that go to the board so that you can attach it to the probe on your meter instead. The other probe goes to where the wire used to be.

http://sub.allaboutcircuits.com/images/quiz/01699x02.png

Notice in the picture... as long as the meter is in the direct path of your circuit, you can get a current reading.
 

(*steve*)

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Alex, if you're waiting, Gryd3 has explained exactly what I mean.

I like using 9V batteries or battery packs with 9V style clips because they're so easy to unclip one side of, and measure current. They remove the need to cut or desolder wires or find some other way to place your meter in series with the load.
 

Alex Scott

Jul 3, 2014
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Hey guys, so I did as instructed by Gryd3 the diagram helped, thank you. My multimeter shows a reading of 8.3v, HOWEVER there appears to be no power going to the board. When I turn the board on, no LED's shine and no siren is made.

I had it set up like this, I tried it other ways but got no readings.

Multimeter red/voltage meter connected to positive on 9V battery.
Multimeter black/common meter connected to negative on 9V battery clip.
Alligator clip between 9V battery and 9V battery clip, the readings dropped to about 7.2v as I write this.
 

Gryd3

Jun 25, 2014
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Hey guys, so I did as instructed by Gryd3 the diagram helped, thank you. My multimeter shows a reading of 8.3v, HOWEVER there appears to be no power going to the board. When I turn the board on, no LED's shine and no siren is made.

I had it set up like this, I tried it other ways but got no readings.

Multimeter red/voltage meter connected to positive on 9V battery.
Multimeter black/common meter connected to negative on 9V battery clip.
Alligator clip between 9V battery and 9V battery clip, the readings dropped to about 7.2v as I write this.
Because you were measuring the wrong thing ;)

When you put your meter in between your circuit like you did, you should be measuring 'current', not voltage. What you have essentially done is put a very very large resister in there which is topping the circuit from functioning.
Take a look at your meter, it may have more than one receptacle for the red lead. Please make sure you are using the one marked for 'mA' or 'A' (These are common markings, but not always present)
If you only have one spot for the red lead, then leave it in there.. Change the mode of your meter to measure current then try again.

Your meter may have multiple ranges of current that is can tolerate, but should also list a 'max' try to never exceed this value or you can damage your meter.. also, if you are unsure what your circuit 'should' draw, try on the largest range first, and if the reading is too small move to the next smaller range until you get a nice reading on your meter.



When you measure voltage. You do not need to disconnect the part you wish to measure, you can leave things plugged in and running. This was one of the steps mentioned above to find the voltage across the IR LED. Turn the devices on and put your meter's probes on either side of the IR LED. this will tell you the difference in voltage from one side to the other of the LED. (Or voltage drop)
0V means that the LED is shorted out, or that it it not being powered.


Meter Use Summary:
Measuring Voltage - This will show you the 'difference' in voltage from the black lead to the red lead. This mode requires the circuit to be live so that you can determine if the voltage levels across components, or at specific segments are as expected. (This will turn your meter into a very very high value resistor)
Measuring Current - This will show you the current going 'through' the meter, and the meter only... To determine how much current is travelling though your circuit, you will need to interrupt your circuit and place your meter in line with it so that is directly in line with the current flow. (Usually between one of the battery leads and the rest of the circuit. (This will turn your meter into a very low value resistor)
Measuring Resistance - This will show you the resistance of the circuit or component you are measuring. To be able to measure a single part, you will need to disconnect at least one leg of the part so that you don't unintentionally measure the effective resistance of anything else in the circuit. (This will turn your meter into a low power voltage source. Care should be given to not use this mode on a 'live' circuit)
 

Alex Scott

Jul 3, 2014
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Gryd3, thank you for the detailed response I followed your advice and it worked. Using the "20" setting on DC current, I got a reading of 0.02A. This time the siren worked and the LED came on. I'm guessing this current isn't correct, it is too low?
 

Gryd3

Jun 25, 2014
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Gryd3, thank you for the detailed response I followed your advice and it worked. Using the "20" setting on DC current, I got a reading of 0.02A. This time the siren worked and the LED came on. I'm guessing this current isn't correct, it is too low?
If you set your meter to '20' that means that it will correctly show "up to" 20A... which seems high for a meter.

0.02A is 20mA which sounds reasonable... I lack a little in field experience so to be certain I would have to do some reading to determine the typical current draw of the components on your board.

What you can do in the mean time... if you have enough hands is try the TV remote trick mentioned above to see if the current draw changes. (Set your meter to a smaller value and you'll get a nicer number ;) )

Also, have you tried setting your meter to measure the voltage across the LED's on the transmitter?
This would help determine if the transmitter works which could help save us time on troubleshooting the receiver.
 
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