Using the RepRapFirmware Configuration Tool
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Looking at those schematics, the positive feed to the endstops is meant to be through a current limiting resistor that is on the main board. These resistors are R52, R56 and R60, but no value for them is provided in the BOM.
The endstop itself has a visible LED in series with the IR LED inside the opto switch, but no current limiting resistor.
Here are two ways of making those endstops work reliably with a Duet:
1. Instead of connecting the positive feeds to the endstops to the +3.3v (centre) pins on the endstop connector, connect each one through a series resistor to either +5V or VIN.
2. Remove the visible LED from the endstop board and replace it by a resistor. A value of 180 ohms in a 0805 package should be about right.
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Ok, the first looks easier for my limited abilities. What value should the in series resistor be?
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If you feed them from 5V then I suggest a resistor of around 180 ohms.
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OK, but R52, R56 and R60 were doing the job previously, maybe I could take a chance with those even though we don't know their value?
Could I possibly replace the LED on the sensor with one of R52 etc? I've never tried anything like this, so I don't know how take a component out of a board and solder back into place somewhere else. Is it hard?
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If the voltage fed to the endstops through the resistors is +15V as implied by the schematic, then the values of R52/56/60 will be too high. OTOH there are several 330 ohm resistors listed in the BOM for that board. Those may well work in place of the LED on the sensor, and if they don't you can solder a second one on top of the first to use two of them in parallel giving 165 ohms.
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OK, basic tutorial on the process. Heat up soldering iron, place on one side of resistor until it melts and pull off with a pair of tweezers? Never done anything this small before!
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SMT can be de-soldered one end at a time, With patience and a fine tipped soldering iron.
Using a TINY screwdriver to move it up, wedge it up, just the smallest amount as each end is heated in turn. It won't even look like it is moving because the "other" end is still soldered. Eventually, it will pop loose.
Re-soldering a new one is relatively easy. One end at a time.
And… if you happen to own a "Temperature Controlled" soldering iron (station) already, it may be worth it to you to invest in "Solder Tweezers" that plug into your existing station. Depending on what station you already have, they can be fairly inexpensive. Examples: http://www.ebay.com/bhp/desoldering-tweezers
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Ok, brilliant. I'll have a go. There are several resistors of that type on the old board, so I've got a few chances! Many thanks.
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My god, my soldering wouldn't win any prizes but the bugger works! Huzzaah! Had to use an old fly tying vice and a gas powered soldering iron on something about a millimetre square was not pretty.
That was before soldering. Too embarrassed to show you it all afterwards!!Many many thanks for all your help.
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Ok, despite working if I plug it in to a board that's already switched on, when I turn it on from cold the duet now fails to boot.
I can disconnect it and it boots fine, connect it and it works fine. Just can't leave it plugged in if I want to boot…
I do hope the answer to this isn't soldering another 330ohm resistor on top of that one. :-0
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Check that you used the correct resistor, and that you don't have a solder bridge across the resistor.
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Yes, right resistor (R37). You see the 330 ohm value in the photo. Not sure about the solder bridge.
But one other thing, if I boot from just a 5V input (usb), it boots up fine. All the endstops trigger and show hit in the machine properties.
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10 mins later...Mmm, after more testing I'm not quite sure what to think. Could be a weak wifi possibly. I just rebooted with the usb and 15v connected and it's fine and dandy. Repeated it with the usb disconnected and again fails to boot. Plugged it in again and bingo!
TBH, if that's all it takes I'll live with that. It's just an OctoPi I use for the camera, so it'll stay on the printer anyway. Be nice to have an explanation though...!
