Telecomms
Manual exchanges
Circuit diagrams and operation of the C.B.S. 2 manual exchange system.
The first one-piece telephone
The Telephone No.332 was the first GPO telephone to include a bell. The anti-sidetone line-matching circuit is really quite ingenious.
The very first telephone
Philipp Reis made a working telephone in 1860 - long before Alexander Graham Bell - from a knitting needle and an old cigar box.
Cheap trunk calls in 1934
In 1934, the Postmaster General decided that evening trunk calls should cost a shilling. The result could have been predicted ...
Physics
Energy in capacitors ...NEW
If a capacitor can hold a joule of energy, how much energy does the same size battery hold?
Capacitance ...NEW
The electric field, flux, potential, what a capacitor is, what it looks like, and how you make one.
Electric charge
What it is, and how Millikan measured the charge on an electron using a stopwatch.
Engineering
Cavity magnetron
How it works, and how it was used with Britain's Chain Home wartime radar defence network against night bombing.
Schmitt trigger ...NEW
How to design a Schmitt trigger with specified threshold voltages, using two npn transistors.
Product design
The process of designing a product to meet the user's needs is not always straightforward.
Heatsinks and reliability
The hotter a transistor runs, the shorter its life. Reduce junction temperature to improve reliability. This is how to do the sums.
RC network design
Understand and design resistor capacitor networks that meet specifications, including how to make low pass and notch filters.
Time constant ...NEW
How capacitors charge, plus the meaning and use of the idea of 'time constant'.
Useful formulas
Useful expressions for sin, cos, tan, log, ln, e, binomial, RMS, stray C, energy storage, complex numbers, arith. & geom. progressions, etc.