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Printrbot Talk Forum • View topic - Opto End Stop

Opto End Stop

Talk about modifications to the printer

Opto End Stop

Postby jafenske » 2013-Oct-Sat-14-Oct

I was inspired by RetireeJay and his opto z stop. You can see it here, . I found this schematic on reprap wiki (http://reprap.org/wiki/Gen7_Endstop_1.3.1) and I got out my breadboard and wired it up, refer to the picture below. You can't really see much in the picture, but that doesn't matter. The circuit behaves the way I would expect it to. When I interrupt the opto switch the LED lights up. Here is my question, I want to ensure the opto switch behaves like the NC mechanical endstop because I don't want to make any changes in firmware. My track record with firmware changes is not very good. I measured the voltage across the positive terminals of the opto switch and it was ~5.0V. When I interrupt the opto switch the voltage falls to ~3.8V. Is that the correct behavior? I am verifying the operation of the opto switch correctly. Thanks for the input.
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Re: Opto End Stop

Postby RetireeJay » 2013-Oct-Sat-15-Oct

When the optical path is not interrupted, your "signal" voltage should be 0.4V or below. The receiving phototransistor is "shorting" the signal to ground (pulling 5mA through the 1K resistor R2).

When the optical path is interrupted, your LED should light up and the "signal" voltage should go to 4.0V or above. R2 (1K) is connected from +5V to Signal, and R3 (2.2K) is connected from Signal to the LED; the other end of the LED is grounded. If there were no LED connection, then the output voltage would be 5V, but the current to the LED through R3 draws it down some, to the ballpark of 4V.

So it sounds like you don't have it wired up correctly. The logic of the Gen7 endstop is correct, so if you manage to duplicate their wiring, it should work for you without software modification.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
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Re: Opto End Stop

Postby RetireeJay » 2013-Oct-Mon-13-Oct

Are you making progress?
I decided to sketch up the schematic for you in case that might help.
Gen7Schematic004.jpg
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
User avatar
RetireeJay
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Posts: 5014
Joined: 2013-Jan-Wed-13-Jan
Location: Greenville, SC
Reputation: 498

Re: Opto End Stop

Postby jafenske » 2013-Oct-Mon-23-Oct

Just as you said I wired it up wrong. Yesterday, I tried it again and this time, just as you stated, I got 4V between the signal and the ground. Thank you for the help and the diagram. Next, I think I am going to order the 3 pin connectors and hook the bread board to the printrboard just to try it. Also, I need to decide how I am going to move the circuit off the bread board. I have been looking for some PCB files so I can order a circuit board. Again, thanks for the help. Thats what happens when you send a ME to do a EE's job.
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Re: Opto End Stop

Postby RetireeJay » 2013-Oct-Tue-09-Oct

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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
User avatar
RetireeJay
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Joined: 2013-Jan-Wed-13-Jan
Location: Greenville, SC
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Re: Opto End Stop

Postby jafenske » 2013-Oct-Tue-19-Oct

Thanks for the info. I saw that web page and I was a little nervous about ordering something from 5000 miles away. But the worst thing that could happen is that I'm out $14. I had another thought but it will take longer. I bought one of these about 6 months ago, . I haven't had a chance to put it together yet but I could use it mill a pcb. What do you think?
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Re: Opto End Stop

Postby RetireeJay » 2013-Oct-Tue-19-Oct

If you want an excuse to build and learn to use your mill, then this is a small project but probably a moderately challenging one due to the required tolerances. Should be fun!

Otherwise, it's a lot easier to just buy. You won't come out ahead on cost by the time you source your circuit board blank (much bigger than the tiny piece you will use) and all the other electronic parts. I bought from Germany and had no problems.
  • 0

Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
User avatar
RetireeJay
My next printer is...
 
Posts: 5014
Joined: 2013-Jan-Wed-13-Jan
Location: Greenville, SC
Reputation: 498


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