Proximity Sensors / Mach3 not showing

**m_c** · 14-06-2013

mycncuksucks

**irving2008** · 14-06-2013

Originally Posted by m_c

Looking at that, the inputs require 7mA at 5V, which somewhat complicates things if using a NPN sensor, as the inputs obvisouly have resistors installed to drive the Optos.

I've got to head to work now, but if nobody has replied by later, I'll figure out some values to use the sensors you have.

assuming 1.2v forward voltage on the opto means that the existing series resistor is (5 - 1.2)/.007 =542, so probably 560R. the suggested series resistors of 1,5k for 12v and 3k for 24v give currents of 6.9mA and 6.4mA respectively.

dropping the 'on' current to 5mA will need a pull up resistor of 220R and the 'off' current through the 220R would be (5-.4)/220=21mA and 0.1W dissipation, needing a 0.25W resistor. I guess 5mA through the opto will be ok and not have noise immunity issues.

It would be better to use a higher supply rail, e.g. 12 or 24v and use the suggested 1k5 or 3k resistors 'off' current/power being 7.7mA/0.1W or 7.9mA/0.2W respectively.

**dudz** · 14-06-2013

Ok... I have a spare PC PSU. 12V (Model LC B200SFX)

If I use this to power the sensor, I connect the PSU -0V to the sensor and to the Gnd terminal on the BOB as shown "right ?" plus the +12V to the sensor input. Using the 1K5 to limit the input to the BOB.
Do I still need a pull up resistor ?..... Its getting a bit confusing for me.

**m_c** · 14-06-2013

6543210987

**dudz** · 15-06-2013

I feel a bit annoyed with myself. I had a diploma in Electronics servicing in 1986. I looked at my college folder from back then, And to be honest I don't understand much of it now. There was more work in Electrics rather than electronics back then, so didn't take it any further.