Count Objects with a LDR and a calculator (help)

[ostef]

[b]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:[/b]

[img]http://www.buildcircuit.com/wp-content/uploads/2010/11/counter-using-calculator.jpg[/img]

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 op the calculator and this is what I can see:

[img]http://i.imgur.com/3dtcuAc.jpg?1[/img]

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 the component VR1 works, since I simulated this circuit with a basci software "livewire", and when I increase or decrease it´s value it doesn´t change anything.

[img]http://i.imgur.com/BQIsUFh.png?1?8754[/img]

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

[url=http://www.buildcircuit.com/object-counter-using-ldr/][size=150]Link[/size][/url]

http://www.youtube.com/watch?feature=pl ... sEGomCY9eQ

[img]http://www.buildcircuit.com/wp-content/uploads/2010/11/counter-calculator1-300x225.jpg[/img]

[pebe]

First, let’s look at how the circuit works. LDR and VR1 form a voltage divider, and the voltage at their junction is fed to the base of Q1. VR1 is initially set so that in normal light the voltage on the base of Q1 is between 0.6V and 0.7V. That is sufficient to turn on Q1 and its collector at R1 will go down to almost 0V. That voltage is fed to the base of Q2 and so it is turned off and the relay is deactivated.

When an object is put in front of LDR, less light falls on it and its resistance goes higher. That takes the base of Q1 below the voltage level that turns it on, so its collector voltage and Q2 base voltage rise turning on Q2 and energising the relay.

You can solder wires to the connections of the “=” button as shown in this video:

http://www.youtube.com/watch?NR=1&v=Ypk ... =endscreen

But if you are not adept at soldering then it might be better if you opt to press the “=” key with a small solenoid, if you can fix it mechanically. The tiny solenoid shown in this link should work the key OK and you can wire it in place of the relay (leaving the diode D1 there).

http://www.ebay.co.uk/itm/DC-5V-Linear- ... 51a63d553f

I hope that helps.

[ostef]

[img]http://i.imgur.com/nZtsZoO.jpg[/img]
Analyzing the tracks, I followed the ones i marked , since that combination closes the circuit with the "=" key. (theoretically, maybe I followed them wrong)

[img]http://i.imgur.com/OSWlu0Y.jpg[/img]

Now in the board , the red lines represent the lines that are in the pcb, So if I understand correctly I would need to solder two thin wires on to those lines to close the circuit and press the "=" key., right?

[pebe]

[quote]So if I understand correctly I would need to solder two thin wires on to those lines to close the circuit and press the "=" key., right?[/quote]
I cannot tell from your photo if they are the correct points. Follow the method shown in the YouTube video.

[ostef]

I have already checked the combinations for some buttons on the calculator, now it´s just time for soldering the cables, I´ll keep the post updated so it doesn´t conclude like this.

[remon7]

i saw these videos...Really its awesome. do u use any sensor or just use a Light. if it block then count. but i need to upgrade it about calculate bar codes, ID card count. how can i do this. Thanks