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Email with document sent Bernt.

_____
Rob
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Pressing the button pulls the converter's control pin high and charges a capacitor.  Output from the converter powers MASTER and the RC keeps it powered long enough for Setup () to pull the pin connected to the converter's control pin HIGH.  If you look at the circuit, you'll see a diode or two, needed to OR some things and protect from screwed-up wiring, and a transistor to invert button HIGH to interrupt pin LOW for waking from sleep.
...still don't get it. How do you wake up the other nodes without the extra wire ?

   Bernt
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AUX and DISPLAY go into sleep, but never actually power down.  Their DC-DC converters stay on with an unavoidable 5 mA quiescent current wasted for each.  When MASTER turns ON or awakens, it starts sending messages.  The sleeping 2551 sees them, its RxD pin changes state and interrupts sleep on the connected CAN board, which then resets the 2151.  Is that clearer?
Ciao,
Lenny
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AUX and DISPLAY go into sleep, but never actually power down.  Their DC-DC converters stay on with an unavoidable 5 mA quiescent current wasted for each.  When MASTER turns ON or awakens, it starts sending messages.  The sleeping 2551 sees them, its RxD pin changes state and interrupts sleep on the connected CAN board, which then resets the 2151.  Is that clearer?
Ok. So you power down only the one node close to the button. I thought it necessary to power down all the bus.

With one extra wire (or a special power button cable), you could remote control power leaving the battery, including that for the power electronics. If this is necessary depends probably on your application. Some 10 or 20 mA overnight, in a every day used wheel chair having a big 24V/80Ah battery, is probably not a problem. But if that is right, why doing so complicated things just for the 5 mA spent in the master node?

   Bernt
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Email with document sent Bernt.
Thank you very much for sharing your work containing years of experience.
Tomorrow we have a 4 person meeting about the protocol. I hope to grasp the important ideas just in time.

Bernt

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Just remember that a lot of that is not appropriate to a CAN network, but you can see the sort of detail I think needs to be defined.

EDIT: and that document would probably be twice the size by the time I've finished.

______
Rob
« Last Edit: June 13, 2013, 11:39:29 am by Graynomad » Logged

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Bernt,

Not quite.  AUX actually turns off power to the Roboteq MCU via a reed relay.  The quiescent current on the Roboteq is > 100 mA.  The reason to turn off MASTER is not to save the 5 mA, but does two things: (1) it makes turning the chair on a slower process, and it actually takes a deliberate push rather than just a tap, so it's less likely to happen inadvertently or with the curious fingers of some toddler, and (2) it forces a reset and startup safety checks of the two critical nodes; MASTER and Roboteq.  My accelerometer shock sensor (an older addition to the current chair) also uses start up after power down to know that it's a good moment to recalibrate.  Waking from inactivity-sleep is not a good trigger for this as the chair would do that, for example, if Rachi were outside working on her tan in our very rough garden, and the chair could wake up while one wheel was on a large pine tree root.

Ciao,
Lenny
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Good morning Lenny,
Not quite.  AUX actually turns off power to the Roboteq MCU via a reed relay.  The quiescent current on the Roboteq is > 100 mA.  The reason to turn off MASTER is not to save the 5 mA, but does two things: (1) it makes turning the chair on a slower process, and it actually takes a deliberate push rather than just a tap, so it's less likely to happen inadvertently or with the curious fingers of some toddler, and (2) it forces a reset and startup safety checks of the two critical nodes; MASTER and Roboteq.  My accelerometer shock sensor (an older addition to the current chair) also uses start up after power down to know that it's a good moment to recalibrate.  Waking from inactivity-sleep is not a good trigger for this as the chair would do that, for example, if Rachi were outside working on her tan in our very rough garden, and the chair could wake up while one wheel was on a large pine tree root.
  • This looks too complicated to me.
    Imagine that you start adding more nodes, complexity will increase further.
  • The wheelchair user can not do a complete system power-cycle.
    I repaired once a "Supertrans" wheelchair with a faulty steering direction feedback potentiometer : when steering hard to one side, the potentiometer gave bad values, the system detected and reported the fault to the user. A power-cycle was necessary, before moving again.
  • Resets and reinitialisation can better be initiated by software.
    If done this way, there is full freedom to do it on every node needed, exactly at the momed needed, for example at power-up, wake-up or after longer stops. And if it's badly implemented you can change mind and recompile without changing the circuit.

By the way, doesn't look the reed controlled full power-down of the Robotec MCU exactly as what is done in Raymarine course computers? Isn't there a simple way to implement it the same way for all bus nodes?

How is it done in commercial wheel chairs? Are there extra connections in the bus cable of your daughter’s wheel chair? (How many contacts has the connector, and do you perhaps have a labelled pin-out for the connector? 

   Bernt



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Hi  Bernt,

I'll respond taking your comments from the bottom up.  You've raised some very important issues that I have to think about, so some of what I'll write here is just "off the top of my head".
Quote
How is it done in commercial wheel chairs? Are there extra connections in the bus cable of your daughter’s wheel chair? (How many contacts has the connector, and do you perhaps have a labelled pin-out for the connector? 
I've attached the manual for the DX-PMB2 power module on Rachi's chair.  All of Dynamic's manuals are available at http://www.dynamiccontrols.com/downloads, but you need to register in some "professional" category to get full access.  I briefly looked for a drawing of the bus connector, but didn't find one, perhaps because it's the one connector that the chair maker doesn't wire; Dynamic offers pre-made cables in various lengths.  I'll try to describe that cable and connector in words.  No, I can do better - I've attached a photo of a piece of old connector.

The cable contains only four wires, and there are no other wires going between modules.  Two are 24V wires that look, by eye, to be about 18-20 AWG that Dynamic rates for up to 12A.  The other two are a foil-shielded twisted pair for CAN-H and CAN-L.  Plug and receptacle are OEM with Positronic machined pins.

Rachi's chair has the following DX modules:
DX-PMB2 - 90A/channel power module
DX-CLAM - combined lighting and actuator module
DX-4SW - takes 4 switch inputs (on a DB9) and translates to CAN messages
DX-ACU - attendant joystick: inductive joystick, user/attendant toggle
DX-SCR - Specialty Controls Remote; the equivalent of my MASTER.  This is an obsolete item; current production is different but functionally more-or-less equivalent.

Dynamic puts the master MCU in the remote (either a full user Joystick or the Specialty remote), while P & G puts it in the power module, but the systems are otherwise pretty similar - ONLY 4 WIRES connect everything.  On Rachi's the bus cables are in a star centered on a "hub" of two DX-4WAY multi-receptacle blocks.

Wiring on Rachi's chair, of course, involves more than just the CAN bus.  There are 2 head-operated and 3 foot-operated switches connected to my 4049/4066 multiplexer, wiring from the multiplexer to the DX-4SW and to a switch-to-USB adapter for her computer, power for an audio amp and the computer, wiring from CLAM to lights and seat tilt and lift actuators, wiring from actuator limit switches to the CLAM and I don't recall what else.  Obviously, I want to avoid adding any more, and indeed would like to reduce the number of connections if possible. Keeping all of this from being pinched somewhere has been quite a task: as delivered the chair was a disaster waiting to happen.  Despite it's CE label, cables went every which way (and were constantly damaged), un-safetied bolts and nuts were falling off, cold solder joints and wires were stripped several cm beyond the connectors, motor wires were lighter gauge than that specified by Dynamic and below the minimum specified by Tyco for crimping, Anderson connectors for the battery cables were improperly crimped and one actually fell out, etc. etc. 
Quote
By the way, doesn't look the reed controlled full power-down of the Robotec MCU exactly as what is done in Raymarine course computers?
I have no knowledge of anything marine, but the Roboteq user's manual (and a lot more) is available at http://roboteq.com/tech-support/manuals-and-software
Quote
Isn't there a simple way to implement it the same way for all bus nodes?
If there were a 5th wire, yes, but I'm trying to avoid that.  I'll add some thoughts about this further down.
Quote
    Resets and reinitialisation can better be initiated by software.
    If done this way, there is full freedom to do it on every node needed, exactly at the momed needed, for example at power-up, wake-up or after longer stops. And if it's badly implemented you can change mind and recompile without changing the circuit.
Yes, but if the only communication between nodes is by the CAN bus, a situation calling for reset may be one in which the CAN bus is down -- there has to be a way to force a complete cold shutdown and re-start as well.
Quote
The wheelchair user can not do a complete system power-cycle.
I repaired once a "Supertrans" wheelchair with a faulty steering direction feedback potentiometer : when steering hard to one side, the potentiometer gave bad values, the system detected and reported the fault to the user. A power-cycle was necessary, before moving again.
That is a common practice for critical faults in WC controllers and in the Roboteq as well, and here you've highlighted a real flaw in what I've done that I must find a way around.  My scheme let's the user cold start the Roboteq and the Master, but not AUX nor DISPLAY.  I don't really care much about DISPLAY, but as AUX turns the Roboteq ON/OFF if AUX goes down the user can't shut things off (someone would have to pull a battery cable).  That's NOT good.  So how can I do this without adding an extra wire even if the entire CAN bus is out of commission?  Dynamic manages to do it, but I don't know how they do it.  My thinking is not fully baked yet, but here's what I'm thinking.  The 2551 CANH pin is 50K impedance when there's no power, and between 2.5V and 5V (more-or-less) when powered.  The Recom DC-DC converter will power on with 1.6 to 5V on its (very high impedance) control pin.  Suppose that an AUX digital pin that is pulled HIGH during setup is connected to the Recom (as on Master) and that CANH is also OR connected there.  Then, during MASTER's power-down routine it could tell AUX to pull that pin low turning off Vcc, and once MASTER was re-started it would put >= 2.5 onto CANH turning the Recom on and re-starting AUX.  All the circuitry needed is already on the DC-DC board, and no more than a few lines of code would be needed to get a full, user-operated, system shut down and re-start.  (NB: the Recom control pin is very high impedance and the pull down on my board is 1M, so this shouldn't interfere with CANH on the 2551).  Just need to connect the Recom control pin (on everything except MASTER) to CANH instead of to the push-button, voltage-divider, RC delay used on MASTER.  Well, seems to be getting better baked with every passing moment.  Thank you for pushing me on this.
Quote
This looks too complicated to me.
Imagine that you start adding more nodes, complexity will increase further.
A few discrete components on the DC board seems a lot LESS complicated to me than running more wires (with more connectors to fail).  Adding another node basically means adding one line
Code:
  NewNode_SLEEPWAKE (State);
in
Code:
void nonMASTER (boolean State)
except that I will probably change State from boolean to byte so that the 3 states can be Wake, Sleep, and ShutOff to implement what I described in the last paragraph.

E' ora di pranzo e devo aiutare Rachi (it's time for lunch and I have to go help Rachi), so bye-bye for now.
Ciao,
Lenny


* DX-BUS cable.JPG (151 KB, 640x480 - viewed 22 times.)
* DX.Power Module B installation manual.pdf (664.69 KB - downloaded 13 times.)
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Hi Lenny,

...found the pin-out of the DX connector on the web (scrolling about half-way down): http://proyectosidesim.blogspot.fr/

So there is really nothing but 2 power-wires and 2 CAN wires. You are right, switching on and off without normal CAN communication between micro-controllers is obviously possible. And it's a really nice solution.

Probably extreme impedances on CAN-L and CAN-H signal switch-on and switch-off. As you describe it or in a similar manner.

(As for the design of the circuit, why would you replicate the power switch in every node, when you could implement one central power-switch reacting to the special signalling.
What would happen for example, if you push the button in a way at the limit so that some nodes wake up, and others continue to sleep?)

Bernt
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(As for the design of the circuit, why would you replicate the power switch in every node, when you could implement one central power-switch reacting to the special signalling.
 
I'm not sure I understand your question as I assume that you are not suggesting that I run 24V up to the user's module (the one with the ON/OFF button) and then 5v from that to all the other nodes.  You may also have missed something from my first post.  I only attached the schematic of the DC-DC converter board that is used at MASTER and said in the description that for the others I'd use the same board with almost none of the components mounted.  To make that clear, I've attached a jpg of what that looked like (until I spent some time at the bench today testing out the "wake by CAN bus" idea - more below).  Those boards are basically just a stackable breakout for the Recom DC-DC converter.  I could even fit what's there on the CAN board if I removed the 4 LED's and resistors, but I've found them a help in trouble shooting (such as the desirability of dumping unread messages that arrive while the system is going to sleep, or the bad 27pf cap that I had on one crystal) without begging use of an oscilloscope or dumping 2151 registers.  I had actually figured on leaving them out later, but given how helpful they've been I've decided I'd rather keep them.

The Recom is a 500 mA 10-pin hybrid SMD with DIP spacing and requires no external components.  I have added a few however: (1) a 10uF input capacitor, recommended by Recom only in systems with large inrush currents which shouldn't be the case here, but better safe than sorry, (2) a reverse voltage diode on the input, to protect against Lenny doing something stupid, (3) an output blocking diode to protect the Recom if there's USB power at the MCU when the Recom is turned off, and (4) a trimming resistor to compensate for the voltage drop of the output diode.

Today I wired up a simple board on a DIP carrier to test out the "turn on with CAN" idea.  I did two things different from my first thoughts of yesterday.  (1) rather than connecting the control pin to CANH, the circuit is CANL--1k--control pin--1k--CANH.  In this way the voltage on the control pin is Vcc/2 whether the bus is recessive or dominant.  (2) I used only this Vcc/2 to turn on and hold on the Recom, and its absence pulled low by a 1M resistor to turn it off.  There are no connections to MCU digital pins at all.  Right now the 3-node net is sitting on the bench cycling ON/SLEEP/WAKE/OFF over and over.  The schematic is in "DC-DC, CAN=ON - Schematic.jpg",

Though this is working well, I will make 2 changes: (1) the CAN physical layer requires that the transceiver be protected from dead shorts between power and signal, and the 2551 actually guarantees survival from -42V to +42V.  The Recom is not, however, protected from overvoltage on the control pin and I will add a 5V or so Zener (far enough from Vcc/2 that the knee is a long way from normal operating voltage). (2) Measured Vcc with the cheap through hole components used was 4.90V and control pin voltage was 2.43V.  That's at the lower margin of acceptable for turning on the Recom and I will adjust the trim to move Vcc to 5.2V (and of course use 1% resistors on the real boards).

So, only MASTER has the ON/OFF/WAKE button, and the other nodes are put to sleep via CAN messaging, or turned off when the power is removed from the MASTER's 2551.  These non-Master nodes turn back on when MASTER's transceiver is again powered up.  I wasn't sure that just powering-down one transceiver would zero the voltage on the CAN wires, but it does.

Quote
What would happen for example, if you push the button in a way at the limit so that some nodes wake up, and others continue to sleep?)
I think that there's good protection from any asynchrony in the sleep/wake/or power-down procedures.  Before sleep or power down, the Roboteq is put in a safe, no output state.  Even if that failed, the Roboteq's watchdog will do the same in the absence of "go" messages.  The wake up routine goes the other way.  To start with, wake up does not rely on the RC delay in any way; its just triggered by LOW on int 0, so I don't know what pushing "the button in a way at the limit" could be.  The Roboteq is not taken out of a safe state until all nodes are awake and the joystick and switches have been checked for neutral.  If a key module should somehow stay asleep even though MASTER is awake, the first message and confirmation request to that node should wake it up - sleep requires an active message, wake up is triggered by anything on RxD, and waking up is completely autonomous to that module.  Even if this failed to get all nodes awake, however, the worst that would happen is that MASTER would have to be turned off and then back on, which, by powering down all the modules, would force them all to reset, including the Roboteq's MCU.

Lastly, I do want to emphasize again that there will be a "desperation" emergency stop that's independent of the CAN net.  A shorted plug in series with the high current contactor coil will be attached to my wrist, and the reed relay controlling power to the Roboteq MCU will be powered from the contactor's output.  If the shorted plug is pulled, all power to the output stages is removed, and the power input line to the Roboteq MCU goes to ground.

Ciao,
Lenny


* DC-DC - Schematic.jpg (39.81 KB, 492x187 - viewed 30 times.)
* Recom R-78AAxx-0.5_SMD.pdf (103.92 KB - downloaded 10 times.)

* DC-DC, CAN=ON - Schematic.jpg (42.06 KB, 492x188 - viewed 28 times.)
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Hi Lenny
There are lots of interesting ideas in your text.
I like the idea of putting a CAN presence detection using two resistors between CANL and CANH. (I would suggest using higher values than 2x1k, because when connecting 20 nodes you get cumulated 100 Ohms, which is too small compared to the cabling impedance and termination resistors.)

For the moment, I do not fully understand the new circuit you are testing. Do you have the two 1k CAN detection resistors on every node ? Where do you connect the power button ? Are you able to power-down the DC converter of every node from a button placed on another node ? How is it possible to power up distant nodes with this detection circuit, when on only not powered CAN transceiver ties the CAN lines to ground, and so impedes the DC converter to switch on ?

Quote
What would happen for example, if you push the button in a way at the limit so that some nodes wake up, and others continue to sleep?)
I'm not sure I understand your question as I assume that you are not suggesting that I run 24V up to the user's module (the one with the ON/OFF button) and then 5v from that to all the other nodes.
Sorry, I was always with my idea of shutting 24V switching power on and off from near the battery, by using buttons connected to any node ("wake-up" in my text meaning power-up with cold reset). When power is switched on, 24V reaches every node and a normal power-up is achieved.

This would be my favourite solution, and with your ideas, it is probably possible to do this without extra wires in the bus. And I feel that processor sleep modes, as well as local DC-converter power-down complicate things unnecessarily : when implementing the possibility to have On/Off buttons on any node, then controlling DC/DC converters locally on each node could lead to some nodes switching on and others not.

Bernt
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I like the idea of putting a CAN presence detection using two resistors between CANL and CANH. (I would suggest using higher values than 2x1k, because when connecting 20 nodes you get cumulated 100 Ohms, which is too small compared to the cabling impedance and termination resistors.)
While I can't imagine a wheelchair with 20 nodes, those resistors could be much more than 2k: the control pin itself is extremely high impedance, and the pull-down resistor I've used is 1M so most all the (CANL+CANH)/2 would be there even with resistors of 10k or even much larger.
Quote
Do you have the two 1k CAN detection resistors on every node ? Where do you connect the power button ?
The CAN lines are NOT monitored on the On/Off board that serves MASTER, but are on all the other nodes.  The momentary contact ON/OFF/WAKE-FROM-SLEEP button is on the On/Off board of MASTER.
Quote
Are you able to power-down the DC converter of every node from a button placed on another node ?
Yes.  Every other node is turned off or on depending on whether MASTER's transceiver is off or on.  One can even see the sequence with which this happens as sending power to MASTER starts its program and then power to the secondary nodes starts up a moment later.
Quote
How is it possible to power up distant nodes with this detection circuit, when on only not powered CAN transceiver ties the CAN lines to ground, and so impedes the DC converter to switch on ?
The CANH and CANL pins on an unpowered 2551 are not pulled to ground -- they are high impedance, see Table 1-2 and paragraph 1.6 of the 2551 data sheet.
Quote
And I feel that processor sleep modes, as well as local DC-converter power-down complicate things unnecessarily : when implementing the possibility to have On/Off buttons on any node, then controlling DC/DC converters locally on each node could lead to some nodes switching on and others not.
Some wheelchair users do not like to have "sleep on protracted inactivity" and prefer to ALWAYS remember to turn off their chair.  Our experience is that this leads to things like a bus driver leaving the chair on and someone hitting the joystick, or the user him/herself leaving the chair on and having some little tyke start playing with the stick.  Those are very dangerous situations.  Even people who'd prefer not to have the chair go to sleep, often chose to leave it on because a re-start takes several seconds.  Then they themselves forget that it's on and catch the joystick with a jacket sleeve.  I've seen too many reports of damaged chairs, broken limbs or even a couple chairs that have ended up at the bottom of a swimming pool.  Now it might be workable to just put MASTER to sleep, but as the Atmega, the 2151 and 2551 all have easily programmed sleep modes, I just say nighty-night to them all.
Quote
Sorry, I was always with my idea of shutting 24V switching power on and off from near the battery, by using buttons connected to any node ("wake-up" in my text meaning power-up with cold reset). When power is switched on, 24V reaches every node and a normal power-up is achieved.
To turn on the CAN lines, MASTER would necessarily have to be receiving power.  If the 24V to all nodes were disconnected down near the batteries, MASTER itself could not be turned on unless it had a separate source of power, i.e. a separate pair of wires.

Now, another small change.  I realized last night while trying to get to sleep that the inrush current into Ctant1 on the On/Off board might compromise the life of the push-button switch, so I've added a 3.6k resistor between ground and the low side of the RC circuit.

Right now I have to try to figure out why our washing machine won't spin, but sometime today I'll change those 1k to 10k to make sure that my inference that the turn on will still work is correct, add that zener, and change the trim resistor to see if I can get an output voltage with a good margin of safety for the MCU yet (CANL+CANH)/2 that's sure to turn on the Recom.

Ciao,
Lenny
« Last Edit: June 16, 2013, 08:37:20 am by LROBBINS » Logged

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Hi Lenny,

It's nearly a week now since your last post, and since  then I was trying to find a solution for the 4 wire system, one with power-up and kill-switches on every node, one that would use your nice CAN-H/CAN-L ground detection, but without extra circuitry on every node. I tried to find a simple scheme to submit you, one with only a central power-switch close to the battery. (I did not find any for the moment.)

This morning, I started changing mind. When reading a very interesting paper about autonomous sail boats [1], I found a comment on energy efficiency and redundant sensors. These boats need extra sensors, but energy is a rare resource, so your local power-down becomes very interesting. And it still does not impede a central node to shut-down power near the battery for safety shut-down and power-cycling-global-reset. This central node would use your CAN-H/CAN-L ground detection.

So I think I will include some extra FET enabling local power of, node by node, something equivalent to your use of the Recom control line. (It would be nice to find a way to power-up individual nodes without doing a sytem-wide power-cycle, but I have no simple idea on how to achieve this for the moment.)

How did you put it? "Thank you for pushing me so far!"

Bernt

[1] :
@inproceedings{StelzerJafarmadar2012,
author = {Roland Stelzer and Karim Jafarmadar},
booktitle = {Proceedings of 22nd International HISWA Symposium},
title = {The Robotic Sailing Boat ASV Roboat as a Maritime Research Platform},
year = {2012},
}
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Hi  Bernt,

Isn't that what this forum is about?  By sharing and critiquing each others ideas all of us can hopefully come up with something better, and yes, you certainly could use an FET or two to do whatever it is that is in the Recom.  For me, it was just easier to use something already assembled and CE certified.
Ciao,
Lenny
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