Ask The Search Engineer

Control circuit . . . PAL devices . . . Torque for screws . . .

Dear Search Engineer: I need a control circuit in which closing it activates a device and closing it again de-activates the device. In other words, push the button and it's on, push the same button and it's off. Any ideas? —R.R. in CA

Dear R.R.: You may want to try using a relay where the push button is connected to an electronic toggle switch. The normally open terminals are between the device and supply voltage and the coil is connected to the controlling dc voltage via the toggle switch.

Dear Search Engineer: Is anyone making low-cost small-scale PAL type devices in the new lower voltage standard (i.e., 3.3V)? If not, then what is being used for simple glue logic in medium-volume designs? Have we moved back to discrete logic components? —H.L., GA

Dear H.L.: Look at the Altera MAX 3000 family of devices. They are inexpensive, operate at 3.3V, and come with as few as 32 macrocells. If you are in need of even fewer gates, take a small step back and look at the overall design and then look at the smallest PIC controllers from Microchip. You can also try TinyLogic and similar families. Otherwise, it seems the way to go would be FPGAs, ASICs, and custom programmed MCUs.

Dear Search Engineer: Any ideas where I can access or purchase a chart for recommended torque values for steel screws in aluminum? —B.F., IN

Dear B.F.: You should check out the torque calculator at the Futek website www.futek.com/boltcalc.asp.

Dear Search Enginer: We manufacture industrial shock absorbers and would like to use a non-metallic, moldable material for our bushings. Typically, we use hard chrome-plated rods with a 25-micron hard chrome layer and surface finish better than 0.5 Ra. The frequency of operation of our shock absorbers is between 20-35 strokes per minute. We need a material in which inside diameters could be reamed or super finished. —P.A., PA

Dear P.A.: Talk to igus (www.igus.com). They make a very wide range of plastic bearings for many different situations. You may even be able to forgo the reaming, as these plastic bushings can be made slightly undersized and wear in themselves.

Dear Search Engineer: I'm looking for some ESD-safe cushioning material about 1/8-1/4 inch thick that will not age or wear and subsequently give off small conductive particles. Right now we use 1/4-inch-thick sheets of black conductive ESD foam but the foam is giving off small black particles, which can then cause electrical shorting problems in the field. —J.S. , CA

Dear J.S.: Try giving Bradford Co. in Holland, MI a call at 616-399-3000. They manufacture ESD dunnage for the auto industry and may be able to help.