Count Objects with a LDR and a how to connect a calculator (help)

[ostef]

Hi guys, thisi s my first post here, and I´m happy I found this site, the circuit I´m trying to make is the following:

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Basically I have to preactivate the calculator so everytime you press the "=" key you get 1+1 and counts evrey object that blocks the light in the LDR.

My doubt is that how do I connect the calculator to the relay, I opened up the calculator and this is what I can see:

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The red spot I marked is the "=" key, since I'm new in to electronics I really don´t have a clue how to connect the calculator to the spot I marked, also I would be really thankful if someone could explain me how the transistors are useful in this circuit (I really don´t know) and if what is the purpose of the component "VR1", since I simulated this circuit with a basic software "livewire", and when I increased or decreased it´s value it didn´t change anything.

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Also here is the link where I found this project and a video.

Link

https://www.youtube.com/watch?feature=player_embedded&v=YsEGomCY9eQ

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Thanks in advance for any help on the matter.

 

[MikeMl]

In normal operation, the PCB traces right under the = key are shorted together by the bottom of the key when the key is pressed. You will need to solder two wires to the two PCB traces. Shorting the two wires together should do the same as pressing the key down. Try it first without the relay. If shorting the wires together operates the calculator as you expect, then connect the wires to a normally open contact in the LDR-operated relay.

 

[dr pepper]

If you look carefully on the calc = button on the pcb you'll see 2 contacts, usually in the shape of 2 E's, one interlocked with the other, what you want to do is follow the tracks that go to each 'E', scrape off some of the green or whatever colour laquer on the board and solder 2 thin wires to it, if you can find an old coil and unwind some of the copper wire this is great for the job as you can fit it in the calc easy.
Connect the calc to your circuit using a headphone connector then you can just unplug it.

You also need to be carefull of background light with this circuit, whatever interrupts the light source needs to make a noticeable shadow on the photocell.

 

[ostef]

If I´m correct this are the two tracks I should solder with wire,
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Where exactly shoud I solder in the calculator?

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[dr pepper]

Not knowing which is the = button thats hard to answer.
The second photo doesnt mean anyhting to me, you only need to solder 2 wires to the = button nowhere else.