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ADJ. INTERVAL TIMER KIT

CAT # MK-111 (8 Reviews) Write a Review

$9.95 each
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Product Description
Velleman # MK111. For intermittent operation of circuits and equipment. Use for blinking light control, slide projector control etc. Pulse time adjustable between 0.5 and 5 seconds. Pause time adjustable between 2.5 and 60 seconds. 3 Amp output relay. Power supply 12-15 Vdc @ 100 mA (not included).

Note: Kits cannot be returned or exchanged once assembly has begun.
WARNING: May cause cancer or reproductive harm.
California Prop. 65
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Customer Reviews (8 Reviews)

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NOT FOR HOUR INTERVALS

Reviewer: from Chicago, IL USA

I've built similar kits to this one. Sahniana asks how to increase the interval from seconds to hours. I *don't* recommend that. The original interval varies from 2.5 to 50 seconds. Sahniana's desired delay is 6 to 12 hours.

Hypothetically, one could multiply the "pause" RC time constant (TC) by a formula. The formula for 6 hours is (6 hrs * (6/5 * 60TC))= 432TC. Double that for 12 hours. Any combination of resistance RV1 and capacitance C2 that produces this product is usable.

Unfortunately, the pots and capacitors would be gigantic (if you could find appropriate parts). Also, you'd have an extremely high-impedance circuit. The leakage in the capacitors and semiconductors would cause unreliable performance. Transistors impose shunt resistances that affect timing. Temperature and humidity would upset operation. Add parts tolerances into the bargain. A 10-percent tolerance means a 1.2-hour error in every 12 hours. Add 10 percent for each 10-percent part! The timer (if it worked) simply *wouldn't* offer a predictable delay. You could get six hours or four.

A CMOS 555 oscillator, a regulated power source and precision capacitors would add back some reliability. You could also build in a C-multiplier. Yet the only sure way would be to use a digital timer.

A MORE PRACTICAL SYSTEM might operate *optically.* For example, you could use a CdS cell (LDR) to switch a relay after sunset. Alternately, you could amplify a phototransistor with one transistor and use that transistor to drive a relay. Wire a capacitor across the transistor base to prevent false triggering by passing clouds. You could probably find appropriate CdS cells, transistors, phototransistors, and relays here at All Electronics.

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A Great Kit

Reviewer: from Jersey Shore PA

Good circuit, but I replaced both pots with 250K units, and replaced both 100mfd caps with 220mfd ones. This give it a nice 2-60 second timing cycles, and with both 250K pots it can be adjusted for any ratio of duty-cycle.

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Excellent Timer Kit

Reviewer: from Brunswick, GA

It's a well done kit that takes only minutes to assemble. A 9vdc-15vdc 'wall-wart' will run it, well. It can be readily modified with a different value timing cap and pulse/pause pots to achieve about any pulse rate and duty cycle within the limits of a 555 IC. Replace the relay with a 1K resistor and it can directly drive a solid-state relay for higher voltage/current loads. No frills ... it just works.

4 of 4 people found this review helpful. Do you? Yes No  Certified buyer

ol faithful

Reviewer: from the Pacific

We ran a few timers during the christmas season 15 hours a day for six weeks. Very affordable and reliable. Easy to change RC constant to vary interval window.

1 of 3 people found this review helpful. Do you? Yes No

Good circuit and easy to assemble.

Reviewer: from Canby, OR

Circuit worked exactly as advertised and the assembly instructions were easy to understand. Kit went together extremely well.

2 of 2 people found this review helpful. Do you? Yes No
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