A simple LED upgrade

At the house warming party we got a bedside lamp with watch from Somi. Since then it was sitting there beside the bed without beeing plugged in. You might wonder why… Because it contains an old fashioned light bulb.

Now it was time to change that. But the project became a little bigger than I wanted…

The plan was replacing the light bulb by a 3W LED and powering it from the 24VDC I have everywhere. But with the removed power cable the light switch was also gone.

So I needed a new light switch. And while doing that I had the idea that I could connect more than one button, one next to the bed, one next to the door, etc…

So the schema grew to this here:


I didn’t have a 78L05 so I made my own version with a few LEDs and a transistor. Works fine for low currents. With three red LEDs I got around 5V.

R1/R2/C1 and U1A are debouncing the button and make a nice clock signal for the D type flipflop. An improvement could be Z-diode to protect the input of the schmitt trigger.

R3/C2/U1B/U1C create a reset pulse to initialize the flipflop to the “off” state after power up.

Connecting the inverting output of U2A to it’s D input makers it change the outputs with each rising clock edge. Exactly what we want. One clock switches on, the next one switches off.

All unused input are connected to some defined level. The schmitt triggers are just connected in a way which makes it easy to solder on protoboard.

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