Path: utzoo!utgpu!watmath!clyde!att!rutgers!rochester!pt.cs.cmu.edu!cadre!pitt!darth!liber From: liber@darth.UUCP (Eric Liber) Newsgroups: sci.electronics Subject: Re: A Challenging PWM Design Problem Message-ID: <412@darth.UUCP> Date: 7 Dec 88 19:17:20 GMT References: <1663@maccs.McMaster.CA> Distribution: rec.ham-radio, sci.electronics Organization: Darth Software, Allison Park, Pa. Lines: 67 > > I have an interesting Pulse Width Modulation design problem; > > Given the following PWM waveforms: > > Minimum pulse width: > > <----------------- 18 mS -------------------> > .--. .--. > ____| |________________________________________| |_____ > > --> <-- > 1.0mS > > > Maximum pulse width: > <----------------- 18 mS -------------------> > .----. .----. > ____| |______________________________________| |___ > > --> <-- > 1.9mS This looks just like a "standard" Model Radio Control signal. By standard I mean from the type of equipment that Futaba, Kraft and others make not what you find at Radio Shack (toys mostly). Anyway there are several "chips" that will do what you want with varying degrees of simplicity. Natioal Semi makes a chip - NE554 that is a servo amplifier chip for model radio control servos. I suspect that with only minor component changes from the "normal" values (and maby the addition of and OP amp for output buffering) it would do very nicely. These are available from digikey and specifications are in the National Linear Data book. If you can't get the data give me a call and i will xerox and send to you. (412- 367 7308 after 7:00 pm). Other possibilities are the receiver chips from National and TI that are complete Radio control Receivers. These would probably be more difficult to use since they have much more circuitry than you need. I don't remember the numbers off hand but the linear data books should have them. Exar used to make a chip similar to the National chip (2264 i think) but i don't know if it is still in production. Last, several radio control equipment companies make digital proportional to motor driver converters. These units allow for input such as you specify and output a varying dc signal to drive high current motors in boats and cars (and electric airplanes!). The units for airplanes are uni-polarity (don't need back up for an airplane :-) ) and are usually bi-polarity for cars and boats. The major disadvantage of these units is that they are typically designed for high current loads (10-200 amps!) and are not especially cheap. One more thought .. I have seen modelers take the electronics from a radio control servo (for an airplane let's say) and modify it to drive a small motor in very small boat models (less than 12" long). These servos are available from various mail order sources in the $9 - $15 range. Get a copy of Radio Control Modeler Magazine to get an idea of sources. Be aware that name brand "quality" servos can run from $30 - $45 and more so if you go this route you want "no name" cheapies. Note that the circuit boards for the electronics in these beasties are small usually less than 1" square (something) like a postage stamp so you are not going to be burdened with lots of real estate. good luck .. if i can help some more please ask. Eric (the red) Liber