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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.

Thaikits – Electronic Kits for Learning

A group of test engineers in Thailand who worked in an Electronic factory more than 12 years have started a small business to sell electronic projects and electronic kits worldwide in 2007.

CH012 Transistor Curve Tracer adapter XY Oscilloscopes 2 ranges Bias

Thaikits - Electronic Kits for Learning

Some interesting kits are HHO High Frequency PWM DC Motor Speed Controller 30A, CH018 Cycling Timer 1.5 -180 minutes ON-OFF 12VDC/30A Heavy Duty 110V/240VAC, CH024 ICL8038 Function Generator Sine Triagle Square wave 0.5Hz-100kHz.

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