How many designs today use discreet components rather than LSI and/or SMD?
I just had a 6-years old domestic carbon monoxide detector reach its expiry date, so thought I'd have a look inside. It was made entirely of discreet components - no LSI, and not a single SMD. Photo here:
One other odd thing was that the device used red, yellow, and green leds for display (removed before I took the photo - they were at the top of the board), and weren't soldered in. They had been pushed into soldered-in sockets. These devices are produced in their millions, so I would have thought it worthwhile saving a few fractions of a cent or penny here and there by using the cheapest component count and construction method available.
I couldn't find an online circuit for a CO detector using a PIC16F676 and Sixth Sense ECO-Sure (2e) CO sensor. The nearest was a Zilog Z8 also using a smoke detector: leading to:
One other thing. It was powered by three Duracell alkaline AA cells. Duracell really are crap; two of the batteries were leaking - see connector at top of photo.