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Author Topic: Laser Detector with Triac and fade-in, fade-out  (Read 7342 times)

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alex.radu

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Laser Detector with Triac and fade-in, fade-out
« on: November 08, 2011, 13:24:44 PM »
I'm making a project for my room. Here's the idea: everytime somebody interrupts a laser beam, the device will trigger a triac in a fade-in effect, in about a second (incandescent light, about 300W). After 15 seconds, the circuit lights will go out in the same fade effect. My idea is to trigger a fade in fade out circuit with capacitor and a transistor. An LDR will sense the light from the laser diode and will feed the transistor from fade-in circuit. This is also a project for school, so, it can't be done with PIC for the moment.

http://pcbheaven.com/circuitpages/Voltage_Controlled_AC_Light_Dimmer/

Now, i'm trying to adapt this circuit and i'm stuck at the control voltage of the 555 timer. Since the simulations of the original circuit with LTSpice and Multisim are different, i'm asking you what software to trust. Multisim crash with the standard circuit so, LTSpice is the software i'm using now.


Sorry if the image is too big.

This is the configuration that gives the widest output (about 90%)
With R12 set to 61 ohms the output is set to low. About 2%

If there are any ideas, please let me know. All the best and thanks a lot!

George

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #1 on: November 08, 2011, 13:33:26 PM »
An Idea - why not breadboard it - and do some real engineering - instead of relying on simulation software written by someone else

alex.radu

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #2 on: November 08, 2011, 17:37:23 PM »
I totally agree with you. In few days i will have the components and will give it a try. If i understand the logic it will be perfect.

For now i think i need some theory to understand what is doing Control Voltage pin because i've run a lot of simulations and it's very blurry in my head. So, if anyone have an idea about how to modify the pulse width with a push button in about a second, please tell me.

George

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #3 on: November 08, 2011, 17:48:47 PM »
Good work - often we use tools we do not understand - - when you do it yourself you will understand it better - and feel great that you did it yourself.

View/watch a few of the tests/experiments on pcbheaven - it is all about giving you the power to learn and understand things yourself.

kam has put an exceptional group of training schemas on this website - view them and learn - and go research your own ideas.

Cheers

George

kam

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #4 on: November 08, 2011, 21:37:55 PM »
An Idea - why not breadboard it - and do some real engineering - instead of relying on simulation software written by someone else
Excellent idea ;) I never use simulations. MOFITO (My Only Friend Is The Oscilloscope).

May i add: You are messing with 220V. Anything above 50V is lethal. When i mess with 220V, i have always a wooden platform underneath my chair, so i do not ground myself directly to earth. This is the least you must do, and you do it at least.

Without a microcontroller it will be a hell for you - trust me. Analog electronics are so nice and so cool, yet again so difficult to make. If you do not know anything about transistors, how to calculate and design a transistor amplifier of any type, then i suggest you teach yourself transistors or choose another topic. Moreover, an oscilloscope is the key to your success. No oscilloscope means 90% no success.

You can read the 555 theory page that i wrote some time ago. If you know how a relaxation oscillator works, then you will certainly understand what this "control" pin does.

Now, regarding your idea, this is what you will need: A 555 connected as one-shot will be triggered by the laser beam. This 555 will generate a 1 second pulse whenever the beam is cut. The pulse will trigger a fade-in fade-out LED circuit (you can try with my design). The output of this dimmer will be driven to the control of the dimmer. I just explained the block diagram of what you need. Now, in between each block, there may be one or more transistors, either to amplify the current, or to scale the voltage of the previous stage. For example, control pin may require 3 to 10 volts for 0 to full brightness, but the dimmer may output 3 to 5 volts. You need to scale this level from 3 to 5 up to 3 to 10 with a transistor.








alex.radu

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #5 on: November 09, 2011, 00:13:52 AM »
First of all, i would really like to have an oscilloscope! I have some oscilloscopes at school and i could use them.

It may be wrong, but i would like to test my circuit (in this early stage) only in low voltage, just before the triac. My lack of experience can't  tell if is ok to test it without seeing the bulb lighting. So, now i'm asking you if this is ok.

Since i've been told not to use simulations and the missing oscilloscope, i hope to be forgiven... I'm using simulations because it's the only way for me to interferre with electronics at this point.

About the 555, i will study in depth tomorrow.

Thanks and a nice evening!

kam

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #6 on: November 09, 2011, 13:11:05 PM »
if you do not connect the 220v on the dimmer circuit, then there will not be any trigger pulse from the zero cross detector, so you need to have the 220. On the other hand, you may avoid connecting 220v to the triac, that will be fine, but how do you know then that the circuit works?

first things first. prototype the 555 dimmer and make sure that it works, and that you understand how to set the R9. At this point, an oscilloscope would save you from a LOT LOT of trial and error. When your dimmer works, go ahead and make an LED delay. Make sure that it works, and then connect them together.

alex.radu

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #7 on: November 09, 2011, 20:54:27 PM »
I'm planning to test the circuit without the triac, but the transformer on. I want to see if there are any delays. The circuit will be tested

Past night i had an idea. I set the CV potentiometer to 50% and adjusting R9 as a standalone resistor. Cummulated with R8, the resistance was 3.6K. Then i was adjusting the CV potentiometer to see the voltage limits when the pulse is wide open or just a short one (with respect to the semicycle). Then i added an equivalent resistor (750 ohms) between VCC and CV pin to feed the maximum voltage (about VCC minus 1V) and a capacitor of 0.5mF to the ground. When the simulation begins, the capacitor is empty and CV is about 0V and the pulse is at it's maximum width. When full (after about 1.5 sec), CV is VCC minus 1V and the pulse is very tiny but happens every semicycle. In this evening i'm planning to make a voltage divider (it's pretty hard for me to think how the circuit will work) and set the minnimum voltage to be just above 0V where the pulse is wide open. I think a transistor will trigger the filling and draining of the capacitor.



I want to mention that everything that i read here is considered. I'm just curious if this idea is feasible.

Now i'm beginning to read the 555 theory page. Wish me luck.

kam

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #8 on: November 09, 2011, 21:18:03 PM »
good luck  8)

alex.radu

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #9 on: November 15, 2011, 19:52:29 PM »
http://www.youtube.com/watch?v=W4bLlzeyT10

I have all components needed now and the circuit is now on breadboard. I was testing the circuit without the triac at the input of the OK is working fine. The R9 potentiometer was measured and will remain set to about 3.6k. Now i'm working on the fade-in fade out circuit. Later on i will post more details about the fade in fade out circuit.

kam

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #10 on: November 16, 2011, 10:29:36 AM »
thanks for sharing alex. What oscilloscope you have?

alex.radu

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #11 on: November 16, 2011, 10:40:30 AM »
It's not mine... GW Instek GDS-2062. The school saves me!

kam

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #12 on: November 16, 2011, 12:47:29 PM »
it is a nice piece of equipment ;) When i was in school, the most advanced oscilloscope that we had these days was a 2-channel cathode ray tube  ::) .... Damn i'm getting older.  :o :(

alex.radu

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #13 on: November 16, 2011, 16:00:34 PM »
I am very happy that i have access to the internet from 3 points, LTSpice and mostly, my DELL La D830. For me, it's the replacement of a real lab. I'm not a poor guy or something (i can afford the components but not the multiturn potentiometer  ::) ), but i'm extremely happy with these tools. I know that people like you really appreciate that two channel CRT oscilloscope at the time. I'm feeling bad when someone does not appreciate a tool, especially from this electronics/IT area.

Greetings from Romania and keep your mind young!

kam

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Re: Laser Detector with Triac and fade-in, fade-out
« Reply #14 on: November 16, 2011, 19:11:25 PM »
if you plan to learn circuit design and if you plan to do some reverse-engineering or other research, you will find out that it is absolutely impossible without an oscilloscope. Its an expensive tool, absolutely important though.