machine stops when homing

[routercnc]

I am using screenset 2010 as well. Next time I'm in the workshop I'll have a look at the config settings.

[routercnc]

Although the homing is working now I decided to have another look at getting the proximity probes to work with my BOB. It is a basic DB25 so won't take the 10-30V direct output from the prox sensor:



Last time I looked at this I tried all sorts of things including resistors arranged as voltage dividers, current limiters, opto isolator boards etc. but nothing worked. I've had one of these relay boards for a while so thought I'd try that:



24V prox connected on one side, and green&white relay contact output cables connect to pins 11 and GND on the BOB.



It worked fine but I know relays are not recommended for homing (or probes) as there is a switching delay of a few milliseconds. But then I wondered if this was a constant delay, and if so, it could still be used?

So I did lots of trials using a DTI and prox set up on the X axis (aimed at a big 12mm bolt head) and it homed back to the same point on the DTI every time without fail.



I jogged away, tried it, repeatedly homed without jogging, jogged to random places then home. Same spot every time. I did 10 minutes of various combinations but each time right back on zero on the DTI. This sounds like even though there is a delay with the relay it is always the same and therefore could be used for homing?

I even tried jogging 0.01mm manually around the switch point and it always tripped on and off at the same point on the DTI. It also showed just how small the hysteris region is on these sensors, and how repeatable they are compared to microswitches.

Perhaps over time the relay switch time could drift, but again unless you have a jig reference point on the board (which I don't), or you are cutting the same part over many weeks/months with lots of homing then that doesn't matter does it?

Thoughts? . . .

[Clive S]

I used to use proximity sensors on 24V straight into the pin on the cheapo BOBs There is a 10K R inside a lot of them so it should only put about 2.4mA into the BOB you can check this by putting your meter on mA range and connecting between the black wire sensor and ground. and see what current it draws. (at your own risk of course)

[routercnc]

Ok cheers Clive. I'm away from the machine for a while now so will have a go at that next time.

[cropwell]

I used to use proximity sensors on 24V straight into the pin on the cheapo BOBs There is a 10K R inside a lot of them so it should only put about 2.4mA into the BOB you can check this by putting your meter on mA range and connecting between the black wire sensor and ground. and see what current it draws. (at your own risk of course)

If you use an external 10k connected to the sensor output, and measure from the other end of the resistor you won't blow the sensor up and you can take that into account in your calculations. I use them straight into the BoB with a 12v supply to the sensor with no problems.
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I have just set up a lj12a3-4-z/bx on the breadboard.
Using a 30v supply the output shows 30v and drops to zero when triggered. BUT the current through a 10k load is 6mA, and without the 10k it is still 6mA. So there must be current limitation.

Then I tried it at 15v and it is the same but 3mA current.