Valentines Day Project for my girlfriend

[Thermal Runaway]

Hi everyone,

Just a quick project I did for my girlfriend this Valentines Day, 2010.  It's just a real simple Multivibrator circuit, with the Q and !Q lines fed to some output FETs.  The reason for such large output FETs was that I also intended to make an incandescent version which would have required much larger current switching capability.

Check it out here:

Brian

[Zero999]

Good work.

Did you use a separate IC/transistors for the multivibrator?

You can make a simple astable with a couple of MOSFETS - no other active components required.

You can also buy pink LEDS to make it a bit more romantic.

A 555 timer is also another simple option.

[Thermal Runaway]

Yeah I just used the standard multivibrator template circuit - two transistors and an RC circuit to alternately switch each transistor on/off.  Then some output FETs to power the LEDs.

I took a look at the pink LEDs but, unfortunately, I didn't have the time to perfect my PCB design to allow for current limiting resistors (I was trying to fit this between work and Uni).  So I just used some LEDs with built in current limiting components, which simplified the PCB design.  I couldn't find any pink LEDs in that form.

She likes it anyway

Brian

[Thermal Runaway]

Next year I think I'll plan something a lot more ambitious

[migsantiago]

Hi, nice project.

How did you arrange the LEDs into a heart form? What software did you use for the PCB?

Thanks!

[Thermal Runaway]

Actually I puzzled over how to arrange the LEDs for quite some time.  In the end I used Microsoft Visio to design the shape I wanted, then extracted the x-y coordinates and used them to place the components in the PCB Design program.  The first design I did sucked because the gaps between the LEDs was not completely uniform, so I did another design using a set length line with end points on it.  The use of a set length line ensured that the gaps between points would always be the same.  I then just copied and pasted the same line each time, placing them end to end and changing the angle of the line to suit the outline of the shape.  Afterwards it was just a case of extracting the X-Y positions of the end points.  There may very well be an easier way though!

For the PCB Design I used Eagle.

Brian

[Zero999]

Yeah I just used the standard multivibrator template circuit - two transistors and an RC circuit to alternately switch each transistor on/off.  Then some output FETs to power the LEDs.

You could've saved a couple of transistors, the MOSFETs could've doubled as the oscillator.

[Thermal Runaway]

Yeah do you know what, I toyed with that very idea but for some reason couldn't get it to work that way in prototype form and... with very little time to spare... I just had to go with what worked.  Thanks for that though

Brian

[Zero999]

I think I know where you went wrong.

You probably just connected the circuit up the same as the BJTs but replaced them with MOSFETs?

The circuit needs to be subtly modified to work with MOSFETS: note the position of R2 and R3.

[migsantiago]

Actually I puzzled over how to arrange the LEDs for quite some time.  In the end I used Microsoft Visio to design the shape I wanted, then extracted the x-y coordinates and used them to place the components in the PCB Design program.  The first design I did sucked because the gaps between the LEDs was not completely uniform, so I did another design using a set length line with end points on it.  The use of a set length line ensured that the gaps between points would always be the same.  I then just copied and pasted the same line each time, placing them end to end and changing the angle of the line to suit the outline of the shape.  Afterwards it was just a case of extracting the X-Y positions of the end points.  There may very well be an easier way though!

For the PCB Design I used Eagle.

Brian

Well, it seems that there is no software for item arrangement on PCB's. Good job!

[Simon]

nice work