On Thu, 7 May 1998 09:00:45 +1000 "Paul B. Webster VK2BZC" writes: >Andres j Ogayar wrote: > >> The idea is having 'something' (read a 555) reading a potentiometer >> position and generating 1 to 2 ms pulses depending on its position >> -1,5 ms will be on the center-. > > Can I suggest you forget the 555s and simplify the thing completely? > Use one measuring circuit (such as a 555 or gate-logic RC timer) and multiplex all the potentiometers into it with an analog switch IC or two. If you use the pulses generated directly over the air, the digital logic is extremely simple. But you probably want to store the potentiometer positions in RAM and do some calculations on them before sending to the radio. During the frame sync pulse, which is much longer than a servo pulse, the transmitter software can measure all the controls since it doesn't have to do anything with the output. Using a PIC with a capture timer should allow a 1 ms pulse to be timed to 12-bit precision. This type of ADC isn't good for general instrumentation use, but for this project it doesn't matter if the end points drift around some. You just want lots of steps for smooth control and the possibility to scale, "mix" and non-linearize the readings later. After measuring is complete, the timer would then operate in the compare mode to generate the output pulses. I'd use a commercial hobby-type RC radio since it is much more powerful than the LM1890-type stuff. The National chips are intended for short-range toy applications. Using real RC radios it is generally possible to control the model from as far away as you can see it. Also it is difficult to build radio equipment (that works well) from the ground up. But you can build your own encoder and/or decoder sections to get the custom features you want, removing the radio section from a bottom of the line 2-channel RC set. Many 2-channel RC transmitters contain the Signetic chip (NE5040??) which is actually a 7-channel encoder. You just need to connect additional pots to the unused pins. Such a modified transmitter would still be "dumb," so including a PIC for digital processing makes a lot of sense. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]