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FrozenGate by Avery

schematic help

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Jan 12, 2008
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I was wondering if anyone could help me with this schematic. Pretty much when a light (or laser) is shone into the photo-cell then the relay switches and the leds turn OFF. Otherwise they are ON I created this schematic myself and was wondering if anyone could check it over and make sure it makes sense. Thanks
 

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Sorry, but this way it can't work, when the transistor close the relay on ground, it also take away the power from the photocell.

First of all, do you need that the leds remains off, when the laser turn off, or just that it turn off the leds, and they go on again when you turn the laser off ?

Second, do you really need to use the relay (like, the contacts do other things, not just turn the leds off), or if there's only the transistor is enough ?
 
Well heres the full story.
I needed a science fair project to make. I wanted to use lasers. So i thought of a system where when a moose crosses through a laser beam then lights turn on warning the driver. I found a diagram to make something like this so i did. I won the science fair and i am now going to the Canada wide science fair (500 people from all over Canada and a few other places) When i get there (in may) they will actually know how to read schematics. I made this schematic from the diagram. I hope this answers your question. Thanks
 
Your Diode is actually shorting out your relay coil and when the transitor
conducts it sees no load except for the diode and will blow..

It would help if you told us exactly what you want your circuit to
do (like the moose project... we know that you want a light to turn
on if something blocks a Laser beam)

Show us your schematic of the the Moose project...


Jerry
 
Sorry for the long wait but i kind of forgot:o. So i made a new schematic. This should make the light turn on when there is not laser in the photo cell. Could you please tell me if this will work. Thank You.
 

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Not exactly right ..... the transistor in your schematic cut out the positive to the base of the transistor when it close, and this cannot work in this way.

Try this one, instead:

attachment.php


not so good drawed, but coreldraw is not the better program for draw schematics :p ..... anyway ..... in this one, the trimmer permit you to regulate the threshold, for take care of the ambient light (is always better to repair the photocell from the most part of the ambient light, anyway, also just placing it inside a little cardboard tube) ..... if the transistor remain on also with the trimmer all in the GND position, it means that your photocell still get too much ambient light, also with no laser ..... in this case, you need to repair it better ..... you can also try to increase the value of the trimmer to 220K, but can't go too far, with the value, so, better take care of the ambient light, before increase the trimmer value (like, placing a cardboard of the photocell diameter around it, closed also on the rear, more long, and painted black inside) ..... and, ofcourse, the contact that you have to use is the NC, not the NO ;)



EDIT: anyway, keep in mind that these types of circuits are a bit unstable, at threshold point, cause they have no hysteresis (this can make the relay "buzz" or vibrate, if you regulate it right on the hysteresis point) ..... you can add an hysteresis, or just play with the regulation .....
 

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so i made your schematic on a bread board and as soon as i add the battery the contact in the relay switches but then no matter how much light it gets it won't change the relay.
 
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Try interchanging the Photocell with the 10K resistor..
What type of photocell do you have... (photo)

Jerry
 
As Jerry said, what "photocell" you are using ? ..... i was supposing you mean a normal photoresistor (a picture can help) ..... also, have you tried to mask it from ambient light ? ..... and, it's still on in any position of the trimmer ?


@ Jerry: in this configuration, it must turn on the relais when a certain amount of light hit the cell (IF it's a photoresistor, ofcourse) ..... swapping them, it's always on, until enough light hit the cell and it become turned off (but in this case, is better to change the resistor with a 100K one ..... is much more easy to turn a transistor on, than off, with this easy schematic ;))
 
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i've tried 2 photo cell on built into a little kit and one from sparkfun
 
I have exactly what i want working using these parts
• 1 Transistor 2N3904
• 1 Diode 1N 4002
• 1 Relay
• 1 Photocell
• 1 10k Ohm Resistor
• 1 9 Volt Battery
• 1 9 Volt Snap
• LEDs
the trouble is i lost the schematic and and the one i have made is glued in a box.
 
As Jerry said, what "photocell" you are using ? ..... i was supposing you mean a normal photoresistor (a picture can help) ..... also, have you tried to mask it from ambient light ? ..... and, it's still on in any position of the trimmer ?


@ Jerry: in this configuration, it must turn on the relais when a certain amount of light hit the cell (IF it's a photoresistor, ofcourse) ..... swapping them, it's always on, until enough light hit the cell and it become turned off (but in this case, is better to change the resistor with a 100K one ..... is much more easy to turn a transistor on, than off, with this easy schematic ;))

That is what he is trying to do... Turn it OFF with a Laser beam on the PhotoCell..

I was wondering if anyone could help me with this schematic. Pretty much when a light (or laser) is shone into the photo-cell then the relay switches and the leds turn OFF. Otherwise they are ON I created this schematic myself and was wondering if anyone could check it over and make sure it makes sense. Thanks

@ jamilm9... We need to know what type of photocell (a Photo or Link would help)..
Is it a Selenium resistive Cell or a Silicone Cell or some other type of Cell.
Each type of cell has different ways to make it do what you want..


Jerry
 
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Ok that is a Selenium resistive photocell...
Use HIMNL9's drawing but put the photocell where the 10k
resistor is and the 10k resistor where the photocell is on the
drawing.

Make sure that you use a 100,000 Ohm Potentiometer or Trimmer
and that your NPN transistor is a good 2N3904...

BTW on HIMNL9's drawing don't forget to put a 300-1000 Ohm
current limiting resistor in series with your LED...

Jerry
 
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So i did what you said but same problem. I think i no why. My pot isn't 100k (more like 5) could this be it. Thanks
 
A 5K pot will not allow you to get enough range...
It is like only being allowed to move the steering wheel in
a car by 1/2 inch to each sdide to get around a tight corner...

Jerry
 





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