Optical speed encoders or opto endstops?

Hello everyone, sorry to bother you with a simple question, but I was wondering if I could just use simple Opto Endstops along with slotted discs from this robot chassis kit or if I should rather use these modules that have a LM393 on it; I know the difference is not enormous, but as I need at least 14 of those, I don't want to buy the wrong thing and neither spend more then neccessary. It does not have to be very accurate. Would the opto endstops work for this? Thank you :-)

//Edit: corrected the optical endstop link

The "opto endstops" in your first link have nothing "OPTO" about them. They're just microswitches.

Sorry I don't know anything about that robot chasis so I can't help, but I'm just saying.

Point #1: You have not posted a design so none of the items you have linked have any relevance until you post a design. Point#2: (the microswitches have no relevance to opto or speed) Point#3: (the optical discs only fit the motor gearboxes sold with the motor kit and you didn't state you plan to buy the whole kit) Point#4: (the opto interrupter works if mounted similar to the one for the robot kit but doesn't come with the opto sensor)

Hello raschemmel , hello KenF! Thank you for the replies.

KenF, I am sorry, I have posted the wrong link. Of course it should be the optical endstop, not the mechanical one :-)


1: do you mean the ciruit design, sketch or the actual endstop circuit board design?

Either way, I have not designed the circuit yet as I do not have any of the sensors yet. I would connect it to an input pin and measure the droven distance according to the slot number and wheel circumference / actual distance per turn.

2: Wrong link, see above, sorry. I ment an actual optical endstop.

3 Yes, I am ordering the complete kit mentioned above, including those geared motors and encoder discs. I am aware that the sensor is not included, thus the question if a simple endstop would be enough, or if it has to be the "speed counter module" sold with the IC.

Thank you for all your time, I really appreciate it. I should have double checked the link... I will edit my previous post, too.

Good grief. That is phenomenally expensive. It looks like one of these but just mounted on a pcb with very little else.

At 80 pence each I’d have said, just suck it and see, but with the prices you’re paying…

Hello KenF, thank s again for your quick reply :-) I think I don't understand, what do you mean? The price of the optical endstop is for 30 pieces (£0.55/$0.89each including shipping), so the board+cable is actually cheaper then the single module from your link. It is not the shop I plan on ordering at, but even in less quantity they only cost 90 cent. As I plan on building a robot with kids, it would benefit to be pre-soldered on a PCB with the right resistors, diodes and the like. The only thing I am not sure about is whether or not the other modules with the IC would have significant benefits (digital output or more obvious feedback, less noise, ecetera).

Unfortunately I do not have any optical endstops at home, just mechanical ones.

Ah that makes more sense. I was reading "30SETS" as their part number. :) But sorry, still don't have any idea of the kit you're attaching it to.


oh okey :slight_smile:
The kit does not really matter, I just hoped for some pointers on what module would be a better choice with a slotted disc and an Arduino, and if the end-stop would suffice.

I have also seen a specific kit for these kind of robots, but they just consist of a similar sensor module and cables, sometimes with black discs, http://www.aliexpress.com/item/Free-Shipping-Robot-smart-car-chassis-speed-detection-module-with-Encoder-disk-2pcs-pack/1359424639.html
Seems like a better fit, but costs more then the chassis kit :smiley:

The is no such thing as a mechanical endstop for a rotating motor gor obvious reasons. Also the optical sensor is your only option with those motors. #1 : by Design I meant Design criteria or Project Objective.

Checking on the price (and watching out for that tricky "10 pieces" in the fine print) There doesn't seem to be a lot in it, price wise. I'd be inclined to go with the LM393 on board. It's more likely to do exactly what you want, straight out of the tin.

Hello Raschemmel, again, I never wrote that I intended to use a mechanical end-stop, I just accidentally copied the wrong search result link. The question is what the difference of the modules output is. Will the opto endstop just output an analog value such as an LDR, while the speed counter module will return a digital output? Before knowing this I can not give you more detail then that I intend on counting the gaps of the encoder wheel...

Hello KenF, yes, some of the offers at Aliexpress have confusing or mismatching quantity specified. I just chose that random link as the images where better :-)

Yes, the difference is just 7-10 dollars or so depending on sensor type and quantity, but I wanted to chose the module that's better suited, plus I am already way over my budget for the kids' project :-) A set of displays here, a bunch of additional modules there... And everything times 6-7... :-)

As no one seems to know how either would perform I guess I have to buy one of each before buying the set, I was hoping to avoid further delay. The opto-endstop was just a random idea as I have used them with the universities 3D printer, and I thought that might be another option.

Yes, the signal out of the lm393 is more likely to be useable without further PCB manufacturing. As far as the mechanical side goes, it's generally quite easy to fabricate something kind of flag that will just hit the sweet spot at just the right time. A piece of card and some precision engineering with gaffer tape will usually do the job. :)

Will the opto endstop just output an analog value such as an LDR, while the speed counter module will return a digital output?

The "endstop" is a end limit sensor. It is either high or low. The other one is speed tachometer used with an optical disk.