Nuts and Volts - November 2011

QUESTIONS & ANSWERS

■ FIGURE 9.

components, so “old tech” is my only present option (iron soldering only).

Note: The pot for speed control can be a mini PCB mount because once it’s set, it won’t be accessible without opening the unit. The sequence should repeat until switched off manually.

— Geoff Mayberry

AAll Electronics does not recognize that part number, but Newark has four units in stock and similar devices are made by other manufacturers. However, I did not find any in stock. The LED is surface-mount but easily hand-solderable. The operating condition is 3.2V, 350 mA (1.12 watts).

The circuit in Figure 7 consists of a 555 oscillator driving a 4017 counter/1 of 10 decoder. Feedback to the reset pin limits the output of the 4017 to one of six. Since only one LED is on at any one time, only one current limiting resistor is needed. The ZVN4210A is rated 100 volts so it can be connected to 12 volt power and survive the load dump transient, but the CMOS ICs have to be protected by R4 and D7. Figure 8 is the Parts List.

I made a layout (Figure 9) to see if the parts will fit in a 2-1/4” circle. It does fit — just barely — and I have the Gerber files. The heatsinks for the three watt LEDs are all connected because it gives greater heat dissipation and the cool white LEDs are isolated; some others are not isolated and should be used with caution. NV

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