Re: IR sensor readings.

Hello all,

Everything seems to work except the IR sensor and the thermistor on the hotbed. So ...

Regards the IR sensor, when I type 'G31' in the serial monitor I get a reading of 1022 which doesn't change if a reflective surface is near the sensor or if I turn the lights out. If I unplug the sensor entirely from the board and do the same I still get a reading of ~340. To my limited understanding this seems like a short circuit? Any suggestions?

Regards the thermistor - hopefully that shouldn't be too much bother but if anyone has a part number just in case I would appreciate it.

Thanks!

Check that you have the IR sensor connector the right way round on the sensor board, as shown in the photo, blue wire on the left, pink on the right.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

@dc42

OK, I double checked it and it looks OK. I shut everything down, restarted and the reading is still stuck at 1023. So I'm off to get a battery for my dusty old multimeter ... (we're a molecular biology lab ).

Sounds like a short on the sensor board between +3.3V (pink wire) and output (blue wire). Check the sensor board for solder bridges.

EDIT: or the ground connection (black wire) is open circuit.

Edited 2 time(s). Last edit at 01/20/2014 08:05AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

@dc42

OK - will get my battery and start prodding it with the multimeter (... and yes, the soldering was awful - tree stumps in puddles of solder - and there was a bridge, but it's not clear whether I fixed it or not.).

Edited 1 time(s). Last edit at 01/20/2014 08:13AM by nipper.

@dc42

One thing ... looking very closely at the sensor board through a magnifying glass the plating doesn't appear to completely line the through hole which links the ground to the side of the board with the bits and bobs on it - there's clearly a ring of virgin green board just below the lip of the hole on the back side. Shouldn't the plating go all the way through (otherwise the ground isn't connected to anything)?

A more obvious fault is that the blue sensor wire is not connected to the correct pin on the Duet, and possibly the connector is on the wrong way around on the Duet too. I just had a customer drive all the way here from Gloucester for me to point that out to him! He had a consistent 1000+ reading, too.

Ian
RepRapPro tech support

Edited 2 time(s). Last edit at 01/20/2014 11:34AM by droftarts.

Quote
nipper
@dc42

One thing ... looking very closely at the sensor board through a magnifying glass the plating doesn't appear to completely line the through hole which links the ground to the side of the board with the bits and bobs on it - there's clearly a ring of virgin green board just below the lip of the hole on the back side. Shouldn't the plating go all the way through (otherwise the ground isn't connected to anything)?

It sounds to me that you've found the problem.

@Ian, looks like he has at least the blue wire connected correctly, because he only gets the 1022/1023 reading when the sensor it connected to the Duet.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

@dc42, @droftarts.

Well, disaster. I got the thermistor and the heating bed working fine - feedback and temperatures all good on the heated bed and the hot end. The motors were (still) working fine. For the IR sensor I put some tinned wire in the through-hole on the IR PCB, snipped it off at the surfaces, squashed it into a rivet (to expel flux from the rim of the hole) and remelted and the ground lines were then all linked up fine. Typed 'G31' and got a lower (but not implausible) reading. But then ... to check the LED was doing something I tried measuring the voltage across the pins on the IR sensor and didn't get anything ... so I tried measuring the voltage at the female socket of the IR sensor at the board (where the female pins are exposed) ... and clumsily bridged with the ethernet and blew the board up. So game over. Since it was clearly my fault I'm going to have to buy another board - what's the turn around time Ian and can I order one from RS?

No, sorry, RS aren't stocking spare parts. Send an email to Sally Bowyer on info at reprappro dot com, she deals with sales, and doesn't have the backlog I do on support emails. If you still need a replacement IR sensor, we'll put one in under warranty. Copy me in too, so I remember!

Ian
RepRapPro tech support

@dc42

(Sigh) You seem to know your way around the Arduino Duet. There's a sadly blackened crater where 'L7' was - if you have a moment could you tell me what 'L7' actually was? Thanks.

L7 is an inductor. Strangely, the parts list doesn't give its inductance, it lists it as "100MHz". It's connected between the analog and digital grounds. It isn't vital, it's purpose appears to be to reduce noise when reading the thermistors. You could try replacing it with a wire link. But it is quite likely that whatever voltage you put across it has damaged the mcu too.

Edited 1 time(s). Last edit at 01/21/2014 11:22AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

@dc42

Many thanks - can you direct me to a schematic and parts list? While I'm waiting for a replacement board I may as well keep myself entertained. I found a source for the MCU online for ~10 euros but replacing that would seem to require some ingenuity.

It's at [github.com]. You need to download and install KiCad to read most of the files, except the schematic which is PDF.

btw I think the inductance of L7 is about 1uH. But as I said before, a wire link should work OK.

Edited 1 time(s). Last edit at 01/21/2014 12:53PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Just a thought about these IR sensors....
Ok it sort of works at one particular range.... So why don't we just mount it so that it's on a slider.
We then adjust it to it's best working range. Tighten it in place and surely it should be ok then.
Or are we saying that the problem is they only work on shiny stuff???? (in which case either sonic or microwaves would be the answer).
Kim

Actually... Here's a random thought....
You can buy dirt cheap low powered laser spotters. Shine it through a pin hole to make the beam smaller. Mount it on the extruder, then sensors on the table that were triggered by the laser that might be a better way to get the X/Y...... Set it at an angle and have a sensor further back on the extruder, then you'd get quiet an accurate Z homing signal to..... Maybe we'd have to print on Ally Plate instead of glass though because of the glass refracting the laser beam... Hmmmm better still if the laser was a CD/DVD laser, wouldn't that work?
Not sure if they might hurt your eyes thou... I don't know enough about them..

Please send the cheque to my home address....
Kim




Edited 1 time(s). Last edit at 01/21/2014 01:13PM by KimBrown.

Quote
KimBrown
Just a thought about these IR sensors....
Ok it sort of works at one particular range.... So why don't we just mount it so that it's on a slider.
We then adjust it to it's best working range. Tighten it in place and surely it should be ok then.
Kim

It's better to change the component values to reduce the sensitivity to ambient light as I did, then you can calibrate it at a lower nozzle height without it saturating. Something like 1mm nozzle height with the sensor face 1 to 1.5mm above the nozzle. Then there is no need for height adjustment of the sensor board.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Sounds good DC.... How do we do that then????

Quote
KimBrown
Sounds good DC.... How do we do that then????

See item Electrical 6a in [forums.reprap.org].

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

@dc42

Right, I'm ordering a new board but in the meantime and (in the name of learning) I'm going to do my best to finish the current one off for good . Never say never! I've ordered most of the bits and pieces that I need but do you have any tips for removing the MCU? I've seen various different strategies but I'm wondering whether they're normally glued down with epoxy?

No, they are not normally glued down with epoxy. You will need hot air kit to remove the mcu. Replacing it is best done with solder paste and hot air. But have you tried replacing L7 with a wire link, in case the mcu is OK?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I've not yet looked at the datasheet for that MCU, but as a thought, where is the download boot code located? If it is in an on-chip EEPROM, a new MCU will need "factory" programming via its JTAG port (or however it's done with that MCU - different processors tend to use different techniques).

Quote
dmould
I've not yet looked at the datasheet for that MCU, but as a thought, where is the download boot code located? If it is in an on-chip EEPROM, a new MCU will need "factory" programming via its JTAG port (or however it's done with that MCU - different processors tend to use different techniques).

I haven't used that mcu before, however from the datasheet, it looks like the mcu has the bootloader program hard coded in it. I think that's why it needs the erase button and the bossac program, rather than the bootloader program used by other Arduinos.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].