Sunday, February 5, 2017

Some electronics fun...

Some electronics fun...  The photo at right (taken with my iPhone peering through a 2x magnifier) shows the current state of one of my projects (I have lots of projects!).  This is the beginning of a touch-activated switch that will go onto the new cabinetry being built for our new mud room.  The cabinetry will hide a three-way light switch for the mud room lights.  This project will let one of the cabinet's knobs take the place of that switch, by toggling the state of a relay each time the knob is briefly touched while the cabinet door is closed.

The stuff you see there is the regulated 5V power supply for the electronics, plus the touch sensor.  The little wire visible coming out from under the top of the vector board will connect to the knob.  The blue 20-turn potentiometer adjusts the sensitivity of the circuit.  The funny thing with a white cap below the potentiometer is a switch, for resetting the touch sensor chip if it gets stuck.  The chip is the tiny little black rectangle with six leads just above that blue potentiometer.  It's the smallest component of all – smaller than the quarter-watt resistors and absolutely dwarfed by the 0.47 microfarad capacitor (the green monster on the right side).

It's kind of mind-boggling for this old fart just how small this stuff has gotten.  I can still remember (not very fondly, actually) when I did all my electronic construction using lug strips and point-to-point wiring, most resistors I used were huge 5 or 10 watt things, and the active components were vacuum tubes with sockets an inch or more in diameter.  Things sure have gotten much smaller!

Much to my amazement, when I finished wiring all this stuff and fired it up, (a) there was no smoke in the air, and (b) it worked on the first try!


  1. When it's all finished and working, I will do that! :)

  2. I looked at this post again and was struck by your reminiscing about lug strip construction. Interestingly, that technique is not dead - hams use "dead bug" construction to avoid the need for a custom PCB. DIP ICs are glued upside down to a copper-clad board and components and wires are soldered to the legs and to each other in the air. More sophisticated dead bug boards will use "islands" as tie points, fabricated by cutting moats in the copper ground plane or by gluing a scrap of plated PCB to the substrate. It can be ugly indeed, for a quick and dirty build, or a real work of art. (e. g.

  3. Here's clickable link to what Richard posted above. That's ... incredible. If you scroll down toward the bottom of that (long) article, you'll see some impressive photos. Electrically that's very much like the lug strip construction I did, except that the lug strips have a bit more freedom in the third dimension (something I made a lot of use of :). But from an aesthetic perspective, that piece of dead bug construction has anything I've ever done beat all to hell!