LED Head

18Nov2007: Once of the electronics wall art / ornaments I have built from Electronics Now July 1994. Its very cool. It has segments for eyes(left-right), ebrows(up-down), and mouth(smile-frown) moving randomly. The video/pictures are below.
The one thing I never liked is that it spends too much time frowning. About 75%. I'd prefer it smiling most of the time. The timer is set for the frown, the smile being the reset. So it can't be changed. So, I figured out that I could change the circuit a bit so the timer is on the smile, with the frown the reset. I have updated the schematic and the pcb to reflect my changes. Reversing 4 LEDs and swapping some ground and +5 volt lines.
It now makes for a much better display.

This is the mouth section of the original schematic. I have labeled the LEDs I am working with LED1-LED4. Unfortunately, this does not match the printed PCB. Probably due to magazine editing.
So I have modified the schematic to fit the actual PCB published in the magazine(resistor placement, LED direction, power). For the Mouth area only.
I then made changes so that the upper LEDs(1 and 2) stay on longest, the lower LEDs(3 and 4) stay on less. Interestingly, this change more closely follows the original schematic.
To see the full size schematic, click the picture.

Here are the steps to modifying the old pcb. Images are looking at the foil side. LED1 is on the top right.

I used a black marker to put a dot on the outside of each LED so I know how to place and rotate them when I put them back.
Use gray wire so it won't show up so bad.
Now the black dots go towards the inside.

The final New PCB with traces changed for the smile. The LEDs are still mounted in reverse. Mount the parts on the non foil side. The LEDs can be mounted on either side.
For the actual Full size version, click the pic. When printing for pcb, print on paper, test IC socket pads for fit, adjust as needed. The print for PCB.

And thats it. Rick D.
If you find this useful, email me.