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Circuit Exchange International

There are ten categories of schematics, a unified circuit analysis, design and theory page, and also a practical electronic section. The simulation section features the “TINA” and “Circuit Maker” programs. (this is a first generation website )

Circuit Exchange International

Some interesting sections are Alarms & Security Circuits, Control & Interfacing, Radio Circuits, Power Supplies & Circuits, Timing Circuits.

Circuit Exchange International


First created back in March 1999 and intended for electronics hobbyists, engineers and enthusiasts everywhere. Currently there are 310 schematics divided into 11 categories. Also included are tutorials, design and simulation sections.  – Andy Collinson

G-switch timer – Vern Knowles

The timer is built using four small inexpensive CMOS integrated circuits. This allows it to run on just 3V from two small AAA batteries. U1 is a 74HC688 8-bit equality comparator. It compares the switch settings to the counter output and will set pin U1-19 low when they match. The actual counter is U2. It is a 74HC4060 14-stage binary ripple counter with built-in oscillator.

The G-switch itself uses a cantilevered metal bar that pivots down as the rocket accelerates upward. The metal bar actuates a small micro-switch that triggers a digital counter to begin the timing sequence. The timer is designed so that it will not start unless the micro-switch has been activated for a duration of at least 0.5 seconds.

G-switch timer - Vern Knowles

G-switch timer – Vern Knowles – The timer was built using a small prototyping circuit board and point-to-point wiring.

U3 is a 74HC74 D-type flip-flop that is used as part of the triggering logic. U3-12 will be low when the counter matches the switch settings. Consequently, on the next oscillator clock edge from U2-9 the flip-flop output at U3-9 will go low. This is the event that activates the 2N4403 transistor that fires the flash bulb.