VGBlog

For PCB project of our Electronics Laboratory course I decided to build a light alarm. It could be used as an alarm for restricted rooms or as a warning for forgotten lights and of course can be improved.

I have used Yenka for circuit design, testing, part list, real-world view and PCB layout. Yenka is really a good tool for Electronics and other topics as Chemistry, Physics etc. as well.

Here is the circuit picture taken from Yenka scene:

3D view of live circuit from Yenka:

By designing with Yenka, I was able to calculate the power dissipation of each object and make adjustments easily. And Yenka was more accurate than other simulation software (timing and current-voltage relationships). Also, I enabled internal resistances.

Circuit is turned on by clicking SPST switch and activated if LDR* gets light. Below, you can see the components are placed on the breadboard.

To see the live circuit on breadboard please watch the movie below:

Light Alarm with 555
.

After recording this video I decided to change the yellow led into green one. That one looked better.

My previous design was without transistor, but green led (yellow in video) was on even though it is totally dark, so I decided to use the transistor as a switch. The part list is below:

Note the bold parts that I used are different than the simulation values. I used 1 ohm for R4 and BC337 for Q1 transistor. You can use almost any general purpose NPN transistors. But check the legs are the same as bc548 or bc337's. The assembly information is given by Yenka, not by me :).

* Resistance of LDR (Light Dependent Resistor) decreases as the amount of light increases. If there is no light, the resistance can increase up to 1M or more and this blocks the current to flow through the 4th pin (reset). 

I dragged and dropped 2D parts into Yenka scheme editor then clicked Export to PCB - Custom (Select thick wires and uncheck "Automatically fill empty areas...". After one or two minutes the components are placed automatically like the first picture. If you click Export to PCB and Open realPCB the following image will be displayed:

If you are not OK with the design, you can change the parts by pressing Ctrl+F12 (Delete red tracks), clicking and dragging components. You can also rotate objects by pressing R key.

The green rectangle shown in the figure sets your PCB board size. You can click and drag to change it. You can see the current size at the bottom-right area of realPCB.

I recommend you printing three images to solder the components succesfully. First realPCB image shown above by printing with the options (Uncheck: All colors black, Check: wires). This will show the circuit that will be seen from the top.

Second (Uncheck: All colors black, Check: Mirror, silk). This will print the image below that will help you to drill the holes.

Third (Check: All colors black, Fill drill holes, Uncheck: Mirror, wire, silk). This will print the circuit that will be ironed onto real copper board:

You should print the last picture with a LASER printer and on a glossy paper. Otherwise ironing will fail. The ink should pass through the copper.

Ironing can take 8 or 9 minutes. After ironing, put the hot copper into a cup filled with water. Slowly rub the paper with your hands to clean. 

After cleaning, put your copper board into Hydrochloric acid and perhydrol mixture. The copper will melt and the following situation will occur:

Clean your circuit with asetone and drill the holes.

Using the first red image with wire. Solder your components.

Good luck...