Wiring 3 wire proximity switches in series

[mikem]

Can someone help me on Wiring 3 wire proximity switches in series. If I run the wires back to my BOB the lights on the switches stay lit and still trigger. I know there is something wrong because the light should be out till it's triggered.

I'm using this switch SN04-N 3 Wire NPN NC DC Inductive Proximity Sensor Switch 4mm Detective Distance with a 24v PS

Link to switch.http://www.ebay.com/itm/SN04-N-3-Wire-NPN-NC-DC-Inductive-Proximity-Sensor-Switch-4mm-Detective-Distance-/272209174995?_trksid=p2047675.l2557&ssPageName=STRK%3AMEBIDX%3AIT&nma=true&si=qi6JMQ6UWvziTgplo1AYFaadbiU%253D&orig_cvip=true&rt=nc

Link to BOB http://www.ebay.com/itm/5-Axis-Cnc-Breakout-Board-Interface-Adapter-For-Stepper-Motor-Driver-Db25-Cable-/381543067417?hash=item58d5bd2f19:g:pPAAAOSwaZdXHuv 8

http://i.ebayimg.com/images/g/pPAAAOSwaZdXHuv8/s-l500.jpg



Any help will be appreciated.

Mike

[lucan07]

I'm no expert but to me your sensors look like they are a Normally Closed circuit and your Bob appears to require a Normally open circuit type of sensor.

circuit would be a ladder

[mikem]

I guess I should have asked it this way.I want to run 1 wire to the switches, instead of connecting all blue wires together e all black together and all brown together is there way to go from blue to black like daisy chain them together?

[lucan07]

if the NC works with your BOB no problem but if your BOB requires NO then ladder is the way

[Clive S]

I guess I should have asked it this way.I want to run 1 wire to the switches, instead of connecting all blue wires together e all black together and all brown together is there way to go from blue to black like daisy chain them together?You have not said what voltage you are using to power them as they will not work correctly with 5V. With that simple BOB you have I would just use standard micro switches wired in series for the limits.

[Neale]

I'm afraid it gets a bit technical to explain why, but you can't just wire these switches in series without knowing exactly which type of switch you have and the kind of BOB input you are using. The switches have three wires, obviously. Two are ground and power in, and the third is one end of a transistor which acts as a switch driven by the clever sensor bit at the blunt end. There are two kinds of transistor - NPN and PNP. NPN (your kind) have this switch between the output wire and ground. That means the load is connected between the switch wire and the positive supply. A PNP sensor has the transistor connected between supply and output wire and load goes between output wire and ground. One of your problems is that the usual simple BOBs need a PNP type sensor because they need a switch between supply and the BOB opto-isolated input. I am skipping any mention of pull-up resistors because these don't work so well with opto inputs.

Then comes the fact that you don't just wire these things in series. In effect, you have to wire each sensor to switch power to the next sensor (if you are using NC sensors). Possible, but you need to know how they work.

Conclusion - with the usual simple BOB, PNP sensors are needed. If you want to wire several together, so any one will trigger the BOB, NO sensors can be wired in parallel very easily, but you lose the fail-safe benefit of NC. I'm about to fit proximity sensors to my own machine; I'm using NPN NC sensors but with opto-isolated inputs designed to work with this kind of sensor and with appropriate wiring, which is not immediately obvious. Or take Clive's advice and use microswitches, which are perfectly fine for limit switches and very easy to wire as many as you want in series!

[Clive S]

Neale. Very well put. :applause: Also some bob's have permanent pull up's so generally just don't work with proxy sensors.