[jimskeet]

Hmm and what purpose does the buffer serve? Does it have something to do with noise filtering or something like that?

[sparkness]

it can provide additional output and clean up the signal , it is a simple amplifier . it cannot isolate like an opto

[john-100]

this is part of the circuit diagram of your BOB

note - this shows only one of the five identical input circuits
also note the missing +5V supply to pin 14
Attachment 386722

the 74HC14 used is a Hex inverting Schmitt trigger

when the input is at +5v the output is at 0V and vise versa

having the schmitt trigger input it also sharpens up slowly changing signals so they have sharp edges

so they are seen as a logic 0(0v) or logic 1 (+5v) not some vague level between 2V & 3V


the 74HC14 has 6 inverting Schmitt trigger circuits inside
Attachment 386724

john

[jimskeet]

Got it. Thanks for the explanation

[sparkness]

not all of the bobs are created equal, one Chinese mfg copies another and gets it wrong and they all look alike. but we buy em cause they look good and are cheap.Then you need to be able to reverse engineer it to fix. I know , I'm guilty.

[coherent]

If this is already standard knowledge then my apologies... Standard proximity switch wiring is brown V+, blue V- & black signal It depends on your sensor voltage ratings but for example if you have a NPN NO sensor that operates on 10 to 30 volts and are using 12v to the brown V+ and have connected the blue to V-/ground... the black signal wire will output 12v (or whatever 10v-30v voltage is supplied to the V+ brown wire) when no signal is detected. When the sensor detects metal the signal wire voltage drops to zero (or close to zero). Most breakout boards are opto isolated from the parallel port which is their typical purpose and have built in pull up/pull down resistors for the input pin signals but, if your breakout board cannot accept a signal voltage greater than 5v at it's input pins, you need to use resistors and make a simple voltage divider to drop the signal wire voltage to 5 volts. Some breakout boards can accept 12v or 24v at the input pins which make things easier. The reason the sensors don't all use lower voltages is the higher voltages are less susceptible to noise causing signal issues. If your sensors have a resistor built in them, then you need to measure the built in resistors resistance and then add the appropriate size resistors so that combined the total drops the voltage to the appropriate voltage that your BoB can accept at the input pins.

[jimskeet]

If this is already standard knowledge then my apologies... Standard proximity switch wiring is brown V+, blue V- & black signal It depends on your sensor voltage ratings but for example if you have a NPN NO sensor that operates on 10 to 30 volts and are using 12v to the brown V+ and have connected the blue to V-/ground... the black signal wire will output 12v (or whatever 10v-30v voltage is supplied to the V+ brown wire) when no signal is detected. When the sensor detects metal the signal wire voltage drops to zero (or close to zero). Most breakout boards are opto isolated from the parallel port which is their typical purpose and have built in pull up/pull down resistors for the input pin signals but, if your breakout board cannot accept a signal voltage greater than 5v at it's input pins, you need to use resistors and make a simple voltage divider to drop the signal wire voltage to 5 volts. Some breakout boards can accept 12v or 24v at the input pins which make things easier. The reason the sensors don't all use lower voltages is the higher voltages are less susceptible to noise causing signal issues. If your sensors have a resistor built in them, then you need to measure the built in resistors resistance and then add the appropriate size resistors so that combined the total drops the voltage to the appropriate voltage that your BoB can accept at the input pins.

Is this necessary? My proximity sensors have been working fine for a year now like this.

[sparkness]

I just made a test setup using an npn sensor and 24v it can only pass 2.3ma so its resistance is about 10k . crap, just blew the fuse again in my meter, seems like I do this all the time, forget to move the test leads out of the current setting.some how I found my spare fuses!

[sparkness]

its fine the input circuit will tolerate this as the sensor will sink current but not source current. Jim I assume that your sensor Black wire is connected to the bob input pin (12) is this the way you have it connected?

[jimskeet]

Cool. One more question. I plan to do some modifications on the machine later this year.
I plan to get a different bob,possibly 12v with an analog 0-10v output for spindle speed control. I will open a thread for bob suggestions when I come to this point. What I want to ask is if I can wire npn proximity sensors in series. At the moment I have 3 different home inputs, a probe input and an estop input. I have no limit switches and rely on soft limits for safety. But I want to add limit switches for the peace of mind. What I am thinking is X, Y and Z home in the same input, Slave A in an individual input for squaring the gantry on ref home, All the limit proximity sensors on one input and the rest 2 inputs, Estop and probe. Is that possiblen

[john-100]

are your sensors normally closed and switch off when they detect the end stop ???

if the sensors are normally open you can wire them in parallel


you can wire normally closed sensors with PNP open collector outputs in series
the output of the first sensor being connected to the positive supply of the second etc

john

[sparkness]

connect n/o switches in parallel. Yes you are correct you just tell mach3 that you have limits using the same pins as the home switches, and A home switch on its own pin so you can square

[jimskeet]

So NpN NC in series is not possible?I would prefer all my switches to be normal closed.

[coherent]

Is this necessary? My proximity sensors have been working fine for a year now like this.

If they have been working fine, then you shouldn't have to change anything or use resistors. It sounds like possibly a ground issue? Remember that DC Neg is not the same as a ground in the way we think of ground. While a DC power supply DC- may be "grounded" to the metal chassis of the unit, some may not be. Grounding your BoB and the DC power supply negative to a common ground may be ok, or may not. It sounds like your parallel port DB25 is "grounded" at it's metal chassis and it carrying the Sensors DC neg or its shorting somewhere and causing issues. You can try a new cable, gender changer etc and see if it helps. In making grounds common there are two trains of thought out there and also it depends on the nature of the separate systems themselves. One example of confusion that is often done in the hobby CNC world is where a PC port is used to control a mains fed spindle controller, the mistaken idea is that using an opto isolator or other means of turning the spindle on isolates the PC from the spindle, where in fact the PC power supply is connected to earth ground and so is the spindle via the grounded neutral, hence no galvanic isolation, just voltage transition. For the most part there are reasons to tie the grounds together.. and reasons not to for "noise immunity",etc that can effect things like sensors. Tying them together is common for simplicity, but if you want to ensure there are no ground issues, isolate DC negatives and run the sensor negative (blue wire) directly to DC neg or BoB ground not a common ground. If there are no bad cables, other hardware, or bad connections and you changed or added hardware, it's possible you introduced a noise issue or did something else which changed the route of the sensors DC neg path causing the problem.

As far as breakout boards the C11 has the analog speed control to replace a poteniometer but it's also a 5v input board. If you have a Huanyang VFD and spindle it may be much simpler to just use the Mach or UCCNC plugin and a $5 USB to RS485 converter and two wires to control the spindle on/off/rpm. When I was dealing with this same issue for proximity sensors I went with a Ethernet motion controller like the UC300 or 400 that has at least 2 ports. It eliminates the parallel and USB issues. Both are more prone to noise or conflict problems. Since you then have another port its pretty simple to then connect another BoB (I used the C80 open collector BoB) that accepts 12-24 volts at the inputs. Last time I talked to the CNC4PC folks they are supposed to be coming out with a new BoB that is 12v, but I have no specifics on it or when.

[sparkness]

I mistakenly used the word ground . I meant the 12vdc negative and is called GND on bob.

[jimskeet]

My sensors are connected to plugs on the control box. at 5e other side the plugs don't have the same colors as the switch. One cable goes to +12v one to input pin and one to ground on the bob. I guess the colors are the ones you mentioned. Would a different wiring keep the sensors working normally?

[sparkness]

I would test with a meter to verify as that seems to be your original concern. I think on your bob both 12v neg and 5v neg are tied together. On boards that I use I keep them isolated

[jimskeet]

What should the meter measure across the wires?

[john-100]

if you must connect multiple normally closed NPN sensors to one BOB input this is one possible solution



John

[sparkness]

you should see 12.xx on the meter with red meter probe connected to brown and black meter probe connected to blue wires of the sensor . when the axis is off the home position and led lit you should measure less than 1 volt across(Blue) GND and (Black) PIN 12 terminal on the BOB this should measure the same for all sensors and there associated input pin