To: File

From: Jon Hagen

Date: 7-21-99

Subject: Biombo Warning Beacon

Attached is the schematic of the biombo. An oscillator with a period of .16 sec drives a 3-bit counter. A decoder identifies the states 1,3,5, and 7. Each of the four decoder outputs enables a 12V spotlight. The four lights therefore blink in succession. Each light has a duty factor of 1/8, being turned on for 0.16 seconds every 1.28 seconds (1.28 = 8 x 0.16).

The counter and decoder are programmed into a PAL 16V8. The oscillator uses a separate 74HC04. (Invertors are available on the PAL chip but they have input protection diodes, preventing them from being driven below ground as is necessary in this oscillator circuit).

The lamps are driven with IRL3303 mosfets which are rated at 38A and 30v with an on resistance of .026 Ohms. The lamps draw about two amperes (nd have a 1/8 duty factor so no heat sinks are needed on the transistors.