autobed leveling using a fsr (force sensing resistor)

this is a litle circuit that i found on ebay. china
it normaly has a light dark sensor
that conviniantly has the same resistance as a fsr (force sensing resistor)
and still is controlable with the potentiameter
that means you just putt the sensor between the carriage for your extruder end the extruder itself
and then you dial in the force so at the smallest amount off pressure the fsr will trigger
at the normal setup the circuit is nc normaly closed butt it has a contact for both

Edited 2 time(s). Last edit at 11/13/2014 09:55AM by brunoschoofs.

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I do not see the picture. Care to provide links?

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Modicum V1 sold on e-bay user jaguarking11

While another option and options are always good, it just seems like a more complicated (and expensive) solution to a problem already solved by other methods.

ETA: Here is an auction that has the part (or one just like it). You'll still need to get a sensor on your own.

Edited 1 time(s). Last edit at 11/13/2014 10:11AM by cdru.

Worth the try, are you already using it? If so, give us some feedback, I might try it.

Hey Bruno; Glad to meet another Bruno.

Would you mind providing the model number for that circuit? I should be able to find it on e-bay or other sources....

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Modicum V1 sold on e-bay user jaguarking11

Wow, that's awesome. force sensing resistor. This could be the change in the future 3D printer model.

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botfeeder
force sensing resistor. This could be the change in the future 3D printer model.

For limit switches, I'm not so sure. A typical mechanical limit switch is a snap-action switch. It's designed so that once a threshold of force is encountered, the contacts snap closed (or open) definitively in a accurate and repeatable manner. Non-mechanical solutions such as a hall effect sensor use a schmidtt trigger (or functional equivalent) to mimic that snap-action functionality. The whole point of a force sensing resistor is that you can measure just so how much force is being applied. For determining if a limit has been reached, knowing that doesn't get you anything more than just knowing if the switch is open or closed....it's by definition an analog device for a digital purpose.

Also for positional accuracy, I don't know if the force sensing resistor would cut it. According to here (which appears to be the same) they are "fairly low cost, and easy to use but they're rarely accurate." Not exactly a good characteristic for something where accuracy is important. I'm sure there's more accurate models out there, but for a higher cost.

Quote
botfeeder
Wow, that's awesome. force sensing resistor. This could be the change in the future 3D printer model.

Anyone see some sarcasm?

If this is to actuate on the bed, it wouldn't work since you don't want anything to be at a lower point than the nozzle

I'm sure we can work something out here.

Imagine a printer can calibrate the print bed and nozzle distance from the bed.
Self calibration:
Allow the nozzle to tap the print bed in 5 different areas ( center & 4 conrners)
From there we'll have 5 force reading.
If the reading is off, the printer can automatically adjust itself. And we can have a balanced print bed.
This will require software to support it.

As for nozzle distance, once we have the accurate reading from the force sensor, we know how much we need to move up the nozzle.
Some time I found the switch sensor is not accurate enough. Especially after thousands of prints.

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To me this solution is more interesting if put on the hot end itself. (The cool side of the hot end) I would love to have one of these sensors with a 2mm or larger hole in it. The circuitry being tunable allows for fine tuning and low force and high accuracy tuning....

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Modicum V1 sold on e-bay user jaguarking11

Hate to burst your bubble guys but this has all been done!
[lmgtfy.com]

Cheers,
Robin.

Quote
Zedsquared
Hate to burst your bubble guys but this has all been done!
[lmgtfy.com]

Cheers,
Robin.

Thank you for your vote of confidence. However most FSR setups have been done with custom circuits, as well as trinkets, etc etc. He is showing us a very cheap circuit that allows us to skip etching pcb's or buying expensive parts. His solution is nearly plug and play... Two pins to solder there, and it allows a trim pot to adjust the sensitivity of the FSR. We have all seen different solutions, he is plainly showing a easy to setup parts......

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Modicum V1 sold on e-bay user jaguarking11

Sorry, didn't meant to come across as too snarky but the discussion *is* going over old ground.

Here's a setup for hot end mounted FSR's for instance:

[www.thingiverse.com]

The proposed circuit is nice and cheap but may have problems that the more FSR oriented "custom" boards don't ... for instance there's apparantly no auto tuning of the threshold, like the code in the trinkets has, so if set too finely you may find false positives a problem or get variations in threshold with temperature.
Also don't probe too fast as that relay has a minimum response time of 4ms possibly up to 12ms depending on how it is driven so you may not get the z probe signal to the board in time before a few more motor steps have been made. On the plus side the relay will probably provide positive audible feedback that the Zprobe is being triggered.

Certainly worth a punt at that price I suppose. Just be aware that there's a wealth of info out there and consult it when debugging.

Cheers,
Robin.

I saw the FSR hot end a while back. I do not like the solution as it is using two FSR's. For me the proper solution may be finding a FSR with a hole in it so the hot end filament can go through it.

In either case, the cost of the circuit is very low compared to other solutions. This makes it a good candidate for testing. It may mean that the solution is inadequate, it could also mean the probe functions with no additional complexity. Having a simple pot to tune the sensitivity may be just what the doctor ordered.

Honestly as of now, none of the FSR solutions entice me. Having a solution that is segregated from the bed is better in my eyes. I am contemplating doing a hall and magnet setup for my printer next and giving auto leveling a shot. Although I have not really needed to level my bed unless I changed the hot end or moved the actual bed.

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Modicum V1 sold on e-bay user jaguarking11

Given the construction of FSRs you might get away with simply punching a hole in the middle, it's not going to break the circuit of the remaining interleaved conductive fingers on the top layer, it might interfere with the way the top layer is held away from the conductive base however. I suppose filament might also drag on the hole edges and have the same effect as pressure on the FSR.
Also watch out for any conductive bits bridging to the base if the hole edge isn't a clean cut... Hmmm ... maybe just punching a hole isn't such a good idea after all

Cheers,
Robin.

[www.a-tech.ca]

This looks cool to me 0-5lb sensitivity.

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Modicum V1 sold on e-bay user jaguarking11

Looks cool, requires an amplifier to feed into a spare a/d on the electronics perhaps (it has a voltage output rather than variable resistance of an FSR) much like thermocouple vs thermistor for heat sensing. Or if just used for an on/off sense then a mod of the light sensor board might work but it's unlikely to just bolt onto the cheap board mentioned above.

Looks expensive too

Cheers,
Robin.

Quote
Zedsquared
Looks cool, requires an amplifier to feed into a spare a/d on the electronics perhaps (it has a voltage output rather than variable resistance of an FSR) much like thermocouple vs thermistor for heat sensing. Or if just used for an on/off sense then a mod of the light sensor board might work but it's unlikely to just bolt onto the cheap board mentioned above.

Looks expensive too

Cheers,
Robin.

I am sure it is expensive. Your right its not an FSR, its a load cell. Meaning it has a voltage input and a variable voltage output. A comparator circuit can be built to switch on a solid state relay at set voltage via a trim pot, at that point all you need is 4 wires for it. Also gives the user a way to preset the trip tension via a voltmeter. That particular load cell looks very expensive. Its advertised as being accurate between 100g - 1kg in most places, or in this case from 0 -5lb..... But no price is available. I have seen some cheaper load cells sell for about 5usd. That particular one may be in the hundreds of dollars, and probably weigh in at a few hundred grams. Making it heavy.

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Modicum V1 sold on e-bay user jaguarking11

From my experience, FSR create a crazy output signal that needs extensive conditioning to get anything that resembles a steady state output. Hopefully, the circuit shown will provide a little signal conditioning.
Good for rough estimates, but not precision measurement.
I think the best way to detect a bed leveling is with a conductor probe touching a conducting surface to complete a circuit. The probe would need to be moved away when printing, but it is very simple and accurate.

Edited 4 time(s). Last edit at 11/14/2014 12:51PM by Easy.