I said, > ... "Hardware design is REALLY the same as software design. You > steal someone else's idea, make a few mods and viola you are done." > I'm sorry that was a very poor choice of words. Copy, reuse and get inspiration from are all better and actually what I meant. The whole history of mankind has been built on improving on someone else's idea. I believe in things like open source and I think I have shared quite a bit of what I have learnt with the rest of group. I do not claim that anything I have done is original but the investigative work did take time and effort and hopefully is useful for other people. What started as a simple joke about hardware versus software design has backfired on me. Sincere apologies, Mike

I'm sure Mike added the tag line in jest, of course; the humor is in it's sardonic truth, but that does not lessen its universal wrongness. Tom Tom Becker --... ...-- GTBecker@GTBe... www.RighTime.com The RighTime Clock Company, Inc., Cape Coral, Florida USA +1239 540 5700

re: "Hardware design is REALLY the same as software design. You steal someone else's idea, make a few mods and viola you are done." Tom, I hope I don't 'touch a raw nerve' here but while I can't speak for Mike, I think the word; "inspired" should be substituded for "steal" ;-) I've learned so much from other folk's examples and have used them in many designs. But they were examples, not IP (Intellectual Property). I still had to adapt them to my environment using good engineering practices. Now, at age 55, I've been giving away a lot of my stuff which takes a lot of my time. My motivation is that my stuff is one, accurate, and two, may help others. If we all had to start from 'scratch', we would probably still be studying vacuum tubes and thermionic emission ;-) Yes, I did that and remember Tektronix curve tracers with both vacuum tubes and early transistors ;-) - Tom --- In basicx@basi..., "Tom Becker" <gtbecker@r...> wrote: > > ... "Hardware design is REALLY the same as software design. You steal > someone else's idea, make a few mods and viola you are done." > > Boo! > > What's this? A page from the Lauton State Penetentiary Pre-Release > Engineering Rehabilitation course? > > Learn from other's designs but don't steal them. Some have lost > original ideas to intellectual thieves and will not, again, find it > amusing. Grrrr. > Tom

I'm sure Mike added the tag line in jest, of course; the humor is in it's...

Mike, thanks. I have a much better idea of what you are doing. You can implement all the states with two pins/motor from the host including breaking. The chip already has the 'steering logic'. As far as current sensing, I see your point. Again while the BX-xx is great, I would 'farm-out' these functions where a slave chip sends one interrupt and the host asks the slave for the interrupt source which is what I'm doing in my latest robot. Given the motor specs, I would normally recommend the TI SN754410 which is a 'beefed up' version of the 'classic' L293D. But since you want ability to 'scale-up' your motors, it would probably not be a good choice. While I'm an old PIC guy, since you started down the AVR path, I would persue that before committing to your current design. You can do all that you desire with a simple H-Bridge controller chip and eliminate all that 'glue'... You would only need a simple serial interface which is why there are so many cheap motor control modules out there that use PICs and AVRs... - Tom --- In basicx@basi..., Mike Perks <basicx@a...> wrote: > Tom, > > Thank you for looking at this and providing some insights. [snip]

> ... "Hardware design is REALLY the same as software design. You steal someone else's idea, make a few mods and viola you are done." Boo! What's this? A page from the Lauton State Penetentiary Pre-Release Engineering Rehabilitation course? Learn from other's designs but don't steal them. Some have lost original ideas to intellectual thieves and will not, again, find it amusing. Grrrr. Tom Tom Becker --... ...-- GTBecker@GTBe... www.RighTime.com The RighTime Clock Company, Inc., Cape Coral, Florida USA +1239 540 5700

Tom, Thank you for looking at this and providing some insights. > > Mike, I've had more time to look at the L6205 data sheet. Before I go > any farther, have you looked at the following ST Micros' App note > AN1762? There is a wealth of info inlcuding schematics of their demo > boards. You can find it here: > > http://www.st.com/stonline/books/pdf/docs/9944.pdf Yes I have seen this and I think every other ST App note. Where you do think I copied my ideas from :) I would really like one of their eval boards. Application note AN240/1288 (http://eu.st.com/stonline/books/pdf/docs/1681.pdf ) gives a circuit for current sensing and short circuit protection (which I don't need with the L6205). It then uses diodes to pull down the input lines. I haven't done this but I think I will but to enable instead. They are easy to add and I would still get the initial pulse to the BX-24 interrupt pin. > > re: 1. > Combinational logic gates that convert the sign/magnitude and brake > signals to the appropriate inputs to the L6205N chip. > [snip] > > Why not let the host processor handle that? You have two pins and > four states for each bridge and it will still require four pins > total. You can easily implement Sign-Magnitude control in software. > Keep the Enables active and apply PWM to the appropriate input. This > is why I would not use a BX-xx for this... I would use a dedicated > controller or program a PIC (or AVR) for this... I also want Brake as well. With my new combinational logic I plan to keep enable high (perhaps using one BX output) and feed PWM either into IN1 or IN2 depending on Direction. I have now successfully built my own dual PWM generator (based on NE556 and LM324) so I will need some logic to combine that in. I have additional logic for the Brake so when it is high both inputs are high (or at least have PWM rather than 0. The logic is: InA = (PWM And Direction) or (PWM And Brake) InB = (PWM And Not Direction) or (PWM And Brake) > > re: 2. > Current sensing logic that compares the sense resistor voltage and > uses a comparator schmitt trigger to signal the BX-24. The idea is > that if the motors get stalled, I want to know about it and cut the > power to prevent burnout. > [snip] > > I see your point. I would take a look at the MAX471 (or similar > current sensing chips). The MAX471 has a built-in current sense > resistor that can handle up to 3A. The MAX472 uses an external sense > resistor for higher currents. Both provide a voltage output so you > will need two A/D channels. They come in 8-pin packages. There are > also many other similar chips from various vendors. Unless you are > really addicted to 'solder fumes' I vote for reduced parts count ;-) After the current sense amplifier I have a test point that I can feed into a A/D. However I like the idea of getting an interrupt rather than polling an A/D. Also the A/D provides an "instant in time" reading. The schmitt trigger, once triggered will stay low until the voltage (current) really drops down again past the hysterical point - I mean hysteresis. Again I like AppNote 240/1288 with its diodes and essentially binary signal. > > re: 3. > Opto-isolators that allow 2 different voltage supplies - one for the > BX-24 and one for the motor controller. I have heard that noise can > travel through ground as well so I wanted complete ground isolation. > [snip] > > Again, I just don't see why you need them here but I really don't > know your application in detail. This is something that needs to be > tested in a `real-world' environment. From what you have described > and looking at your schematic, your power supply design does a good > job of isolating the motor and logic supplies. One key point is > connecting all the grounds to a common power supply ground where the > regulators are connected to the external supply. I think I have the grounds straight in my physical layout. As you say getting that right is key. I think I just wanted an extra safety margin and this might be over-engineered :) > > Finally, what motors are you using? What is the typical current? What > is the Stall current? There are a lot of H-Bridge controller chips > that are a lot easier to use than the L6205... > The motors are in the link I previously sent you (http://www.lynxmotion.com/Product.aspx?productID&CategoryID ). The stall current is 1.5A. I'm also thinking about the future when I move to bigger motors and eventually 4 motors. Obviously for 4 motors I will need my own PWM generators. I think if someone gave me the source code for an AVR one (say on a ATMega8) I would build it. I just haven't quite got to more complex AVR programming myself yet. I would use 4 outputs for PWM and 4 outputs for servo pulses. I built myself a programmer now so who knows I might do this next :) I looked at both the L298 and LMD18200. In the end the decision came down to bending pins or not :) Not to mention that two LMD18200's are really expensive. I wanted to breadboard and then transfer to stripboard and solder. The DIL packaging of the L6205 is just easier to handle. So I think I'm going to plow through this (I have it all working so actually I'm really done except for building it) and perhaps I will look at these other chips at another time. I don't think I am ever going to use a simple FET bridge because of all the added capabilities of these kinds of chips. Thanks again, Mike "Hardware design is REALLY the same as software design. You steal someone else's idea, make a few mods and viola you are done"

Mike, I've had more time to look at the L6205 data sheet. Before I go any farther, have you looked at the following ST Micros' App note AN1762? There is a wealth of info inlcuding schematics of their demo boards. You can find it here: http://www.st.com/stonline/books/pdf/docs/9944.pdf re: 1. Combinational logic gates that convert the sign/magnitude and brake signals to the appropriate inputs to the L6205N chip. [snip] Why not let the host processor handle that? You have two pins and four states for each bridge and it will still require four pins total. You can easily implement Sign-Magnitude control in software. Keep the Enables active and apply PWM to the appropriate input. This is why I would not use a BX-xx for this... I would use a dedicated controller or program a PIC (or AVR) for this... re: 2. Current sensing logic that compares the sense resistor voltage and uses a comparator schmitt trigger to signal the BX-24. The idea is that if the motors get stalled, I want to know about it and cut the power to prevent burnout. [snip] I see your point. I would take a look at the MAX471 (or similar current sensing chips). The MAX471 has a built-in current sense resistor that can handle up to 3A. The MAX472 uses an external sense resistor for higher currents. Both provide a voltage output so you will need two A/D channels. They come in 8-pin packages. There are also many other similar chips from various vendors. Unless you are really addicted to 'solder fumes' I vote for reduced parts count ;-) re: 3. Opto-isolators that allow 2 different voltage supplies - one for the BX-24 and one for the motor controller. I have heard that noise can travel through ground as well so I wanted complete ground isolation. [snip] Again, I just don't see why you need them here but I really don't know your application in detail. This is something that needs to be tested in a `real-world' environment. From what you have described and looking at your schematic, your power supply design does a good job of isolating the motor and logic supplies. One key point is connecting all the grounds to a common power supply ground where the regulators are connected to the external supply. Finally, what motors are you using? What is the typical current? What is the Stall current? There are a lot of H-Bridge controller chips that are a lot easier to use than the L6205... - Tom

tombhandley wrote: > My first question is why all the 'glue' logic? This seems to be way > too complicated for such a simple task even with monitoring motor > stall current. I have no experience with the L6205N but after > glancing over the data sheet, I will probably order some for my > projects. One thing that 'caught my eye' was it's thermal shutdown > mode and the ability to monitor it. I think you can eliminate a lot I experienced shutdown once while testing. I thought I had fried the L6205 (no heatsink on the breadboard). It took about a minute to recover. I want to avoid the shutdown situation (probably doesn't do the chip much good) by monitoring earlier. In my view this is the difference between a flaky circuit and a robust circuit. The same applies to writing software as well. > of analog 'glue' by monitoring the "EN" pin. As far as optoisolators, > I just can't see a need for them in this application if you use a > sepatate supply for the motors and good grounding practice. Again, > I've just had a 'glance' at your design but if you want wheel > feedback, I would use shaft encoders, not relying on measuring back- > EMF. > > The bottom line... I'm impressed with your effort (we hardware guys > normally don't trust software guys with a soldering iron ;-). But I > just can't understand why all the extra 'glue'... Thanks. As I joked with someone else, I miss the smell of soldering and need a fix soon. Mike

Tom, Good idea but as noted in my original append, I really need two independent PWMs (one for each wheel) otherwise turning gets a bit hard - not quite impossible but hard. > > ... a conflict with InputCapture... > > There's an eight-bit PWM available from Timer2 on pin 25, but not dual > PWM like Timer1 offers. I just moved a 112Hz DC motor PWM to Timer2 so > I could use Timer1 as a 16-bit internal timebase. Somehow it feels nice > to have three timers running. > Tom >

> ... a conflict with InputCapture... There's an eight-bit PWM available from Timer2 on pin 25, but not dual PWM like Timer1 offers. I just moved a 112Hz DC motor PWM to Timer2 so I could use Timer1 as a 16-bit internal timebase. Somehow it feels nice to have three timers running. Tom Tom Becker --... ...-- GTBecker@GTBe... www.RighTime.com The RighTime Clock Company, Inc., Cape Coral, Florida USA +1239 540 5700