Can't get home!

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07 Jan 2012 23:40 #16423 by andypugh
Replied by andypugh on topic Re:Can't get home!
fgauder wrote:

The servo drives have a built in feature that inhibits travel in the direction of the tripped limit.


Aha! Why didn't we think of that?

Definitely one to add to the "weird causes to remember" list.

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09 Jan 2012 03:03 - 09 Jan 2012 03:08 #16460 by alexr
Replied by alexr on topic Re:Can't get home!
I dont know if this is any help but it might be some inspiration.

My B.O.B. comes with a 1k pull up circuit for inputs such as limit switchs and e stop.

Im no electronics engineer so i am not sure why they need to increase resistance/impedance, but it was significant in getting my homing NC circuits operational.

I guess what i am asking is 'could it be hardware specific?'

alex


had a quick search and this could be the problem, i hope it helps

www.seattlerobotics.org/encoder/mar97/basics.html
Last edit: 09 Jan 2012 03:08 by alexr. Reason: found something useful.

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09 Jan 2012 10:36 #16468 by andypugh
Replied by andypugh on topic Re:Can't get home!
alexr wrote:

My B.O.B. comes with a 1k pull up circuit for inputs such as limit switchs and e stop.
Im no electronics engineer so i am not sure why they need to increase resistance/impedance


Just for clarification, a pull-up doesn't increase the input impedence, if anything it reduces it.

The computer senses the voltage of the pin, but your external circuit typically works by changing the flow of current rather than applying a voltage.

The pull-up goes between the +5V and the pin, and then the limit switch goes between the pin and 0V / ground / earth.

Think of the resulting circuit as a potential divider. With the switch open there is 1k to 5V and infinity to 0V, so the pin sits at a nice, solid, 5V.
With the switch closed there is still 1k on the 5V side, but 0 ohms on the 0V side, so the pin is pulled hard down to 0V. (and there will be a steady 5mA running from the +v to 0v through the switch.

Without the pull-up and with the switch open the input pin is not connected to anything at all except the wire to the switch. This will tend to act like an antenna, and the PC will detect all sorts of random voltages on it.

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15 Jan 2012 19:28 #16792 by helpmeout
Replied by helpmeout on topic Re:Can't get home!
correct me but i think you need to change the yes to a 1 on home ignore limit. check that...

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