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I've been considering various ways to control more than three output devices with only the three ports and came up with the following idea. I don't have the electrical design knowledge to implement, so if this idea sounds good, I'd like to (...) (26 years ago, 25-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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What about a real time circuit that routed the output power to one of eight output ports depending on the PWM. That way it only takes one output port on the RCX and up to three (out of 24) motors could be running at the same time. (...) like (...) (...) (26 years ago, 25-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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(...) And where are you getting motor drive power from? I assume you want the selected motor to run at full power, not at 1/8, 1/4, etc. I'm afraid you're still stuck consuming the extra output for power unless you use a separate power source. (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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(...) With a seperate battery box (from 8735 for instance) you could power the output full time. In this case you'd probably want to map it to something like this: off - off 1 - output 1 fwd 2 - output 1 rev 3 - output 2 fwd 4 - output 2 rev 5 - (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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(...) There are 8 levels of PWM, so fwd/rev for 4 devices is possible. I originally wanted a separate power input to allow a full 8 levels for each device. This would allow the controller to operate ANY device designed for the RCX ports and not (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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There is no need to waste PWM levels on reverse. You can set the RCX motor output to reverse speeds as well, giving you 7 outputs (fwd and rvs) instead of 3 1/2. You need a bridge rectifier anyway; you might as well exploit it to indicate direction. (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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In my example the RCX output was just used to tell this mythical board which output to drive. Power for the output came from a battery box, always set to on. The RCX can't set direction on the battery box (at least not trivially). alex (...) -- Did (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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(...) Are you sure? I wasn't, so I went looking. The NQC docs seem to imply 7 powers levels plus off. Which, technically, is 8 levels of PWM, but if you use all of them, a motor is running at all times. That is fine if you use another motor output (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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Right. That is why you cannot use all 8 power levels. The polarity reversal that I am talking about is on the controlling (and only) output. I am already assuming, at this point, that drive power is stuck on as with your external battery box. (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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(...) I don't know how NQC drives the ports, but both rcxcc and the RIS software have separate controls for on/off and power level. I just tested setting all 8 power settings - motors operates for all 8. -Wes (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: multi-device output controller
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Thanks for checking this out. This is important to know. I assume, then, that the duty cycles are 1/8 through 8/8 as well as off, which would be 0/8. Can anybody verify this (with a scope or something)? I have long wondered whether the duty cycles (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Why do it? Was: multi-device output controller
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(...) I have checked this out, and if you use the standard RCX firmware (or other firmware that uses the RCX ROM, then you get the waveforms you are talking about at 125Hz 1/(1ms x 8). You also get polarity information - oh no, I've said too much. (...) (26 years ago, 26-Mar-99, to lugnet.robotics, lugnet.robotics.rcx.pbforth)
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| | Re: Why do it? Was: multi-device output controller
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Ralph, Thanks for reigning in the rabbit chase! As the originator of this thread I'd like to respond to the 'why'... I keep running out of ports on my creations. I see 5 or 6 as a practical limit. My criteria for a solution: 1. Entirely compliant (...) (26 years ago, 26-Mar-99, to lugnet.robotics, lugnet.robotics.rcx.pbforth)
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| | Re: Why do it? Was: multi-device output controller
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I think that the solution should also be flexible enough to allow the power to be plugged into either an RCX output port or a battery pack. That way if you didn't want to lug around another battery pack, or if you didn't want to use up another (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | Re: Why do it? Was: multi-device output controller
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My original message described the controller with two inputs, one for device selection and one for device power. This could easily be connected to whatever power source the user desires. (...) (26 years ago, 26-Mar-99, to lugnet.robotics)
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| | RE: Why do it? Was: multi-device output controller
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(...) Measuring PWM is not difficult, but it would involve a micro (PIC12C508 anyone?) dedicated to the task and then you would have to get it to drive the RCX, which means motor drivers, etc. If you are willing to spend $50 and LOTS of time, then (...) (26 years ago, 27-Mar-99, to lugnet.robotics, lugnet.robotics.rcx.pbforth)
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