coupled, the diodes can be omitted. The LEDs can be just about any you may have handy or like the looks of. I mounted them directly onto the circuit board, then ...
58 Pocasset Ave. Worcester, MA 01606 This article describes a compact inexpensive magneto synchronizer I have constructed. The schematic shows a convenient layout for components; the completed circuit fits easily in a 4" x 2" x 1.75" BUD box. I made the entire unit from spare parts I had sitting around, but if you were to purchase everything new, the cost would be under $15. Power for the unit comes from the aircraft battery - one clip lead attaches to
the battery positive terminal. A 9-volt transistor battery can be substituted, requiring either an ON/OFF switch or removal of the battery when not in use. Three other external connections are required: a clip lead to each mag P-lead and a lead connecting the synchronizer ground to aircraft ground. The LM324 Integrated Circuit is a quad op amp, $1.29 at Radio Shack. Each op amp functions as a voltage comparator. A small current is passed through the magneto P-lead to ground: the voltage drop across the P-lead to ground is compared with the drop across the 1 ohm resistor (at the + and -
inputs of the op amp, respectively); resistance of a typical primary coil (in a Slick mag) is a bit more than 1 ohm. When the points are open, the mag coil drop exceeds that of the reference resistor, and the LED (light emitting diodes) is lit; closing the points turns the LED off. If your mag primary coil resistance is lower than 1 ohm, you may need to adjust the reference resistor value. Or you may have a partially shorted mag coil. You could also add buzzers, as do the commercial units; I found them unnecessary. All resistors are 1/8 Watt; they carry very little power. Any values near 1.2K can be substituted, provided they are reasonably well matched. If your aircraft has a 24-volt electrical system and you elect to run the device off the aircraft battery (as I did), change the 300 ohm resistors to 600 ohms (again approximate values) or the LEDs will fail quickly. The back-to-back diodes to ground in the P-lead circuit are protection for when you forget to spark out the impulse coupling and dump the mag pulse through the synchronizer. They will in most cases save the integrated circuit. If your mags are not impulse coupled, the diodes can be omitted. The LEDs can be just about any you may have handy or like the looks of. I mounted them directly onto the circuit board, then used standoffs to position the LEDs in holes in the chassis box. •
Readers are invited to submit entries to EAA, Hints For Homebuilders, Att: Golda Cox, EAA Aviation Center, P.O. Box 3086, Oshkosh, Wl 54903-3086. Entries will be reviewed by a panel of EAA judges. Readers whose hints are published in any EAA magazine will be awarded one of three monthly prizes by Snap-on Tools - a 3/8" Drive Socket Wrench Set, a 1/4" Drive Socket Wrench Set or a Nine-piece Long-Handle Combination Wrench Set. Members are also invited to submit hints of an electrical nature. Any hint used will
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being awarded the best entry for the year. A Grand Prize will also be awarded by the John Fluke Mfg. Co. These awards will be presented during the EAA Convention.
Our thanks go to Snap-on Tools and John Fluke Mfg. Co. for providing these awards. -.,
Most aircraft provide no warning when the engine is stopped and the mag switches are inadvertently left. ON. In this condition, any move- ment of the prop could ...
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After my friendly neighborhood mechanic stuck a jack through the wing of my newly purchased RV-4, I decided to redo the instrument panel while the plane was ...
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SI is left in this position after start up,. LI, or red light, will stay on. Warning horn, HI, is off. After start up (Figure 2), and oil pressure is above 35 psi, SI is placed.
