The IC's basic function is to output a high/low signal at a predetermined rate of speed. Two resistors and a capacitor that are connected to the IC configure the rate of speed. Figure 3 Single timer circuit schematic. cuit that was used as an auxiliary switching device. A switch that was operated by the performer controlled this relay. The auxiliary relay contacts controlled the power into the timer relays. The control system was set up so that there was a master control switch that switched power on to the power supply for the solenoids and to the control circuit. Additionally, each of the timer circuits were fitted with an on/off switch and each of the outputs of the timer ICs had LEDs connected to them. This enabled each of the timers to be configured individually without running the other timers or relays. A rough setting could be established by adjusting the pots and watching the LEDs. Also, the LEDs served as indicators that the timers were running without having the solenoids firing. Although, the overall control circuit and enclosure was fairly tedious to assemble, the end result is that we now have a control circuit that can be used for a variety of applications. A common use for this could be a fire flicker effect. Since the timer relays have 10-amp contacts they could be used to switch relatively heavy loads. CONCLUSION In conclusion the project was very successful and there are only a few choices that we would make differently in the future. * The 20-cubic-foot gas cylinder proved to be too small and needed to be replaced often, we would purchase 125-cubicfoot cylinders if the application allowed the larger size tank. * During the process we changed to argon gas because our local supplier could not provide a quick turnaround on the nitrogen tank refills. Argon is an inert gas like nitrogen and the initial tank pressure is similar (2000 psi). * We would consider using longer stroke cylinders on one or more of the legs to provide more variety. * We would use a larger project box to make fabrication of the control circuit box easier. The planning for this effect made the execution for the show smooth and reliable and has given us a useful piece of equipment that can be used in future productions. Of special note, we ordered all but the cylinders, nitrogen, battery charger, and battery on the Internet. SOURCES / REFERENCE American Cylinder americancylinder.com 708-258-3935 McMaster-Carr mcmaster.com 630-833-0300 (Chicago office) Northern Hydraulic northerntool.com 800-221-0516 W.W. Grainger grainger.com 877-423-7087 Radio Shack radioshack.com 800-321-6475 Digi-Key Corporation digikey.com 800-344-4539 National Semiconductor national.com 800-272-9959 TD & T S U M M E R 2 0 0 1 41http://www.americancylinder.com http://www.mcmaster.com http://www.northerntool.com http://www.grainger.com http://www.radioshack.com http://www.digikey.com http://www.national.com