Wiring 24v NPN Proximity Switch to 5v BOB - Why does'nt it work

**Clive S** · 13-10-2016

Originally Posted by MikeyC38

The switch does have 300ma printed on it. But I think this is too much current for the BOB input.

What that means is that the switch can source 300mA try putting a mA meter in circuit and see what you get.

**m_c** · 14-10-2016

Originally Posted by Clive S

What that means is that the switch can supply 300mA try putting a mA meter in circuit and see what you get.

Not quite, it means the sensors can switch 300mA. It's not supplying anything.
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Most of these sensors have overload protection built in, so if you were to try and switch a load that exceeds 300mA, it would appear to do nothing. However, a BOB opto will not need anywhere near that much current.

**cropwell** · 14-10-2016

Originally Posted by Clive S

What that means is that the switch can supply 300mA try putting a mA meter in circuit and see what you get.

The 300mA is the current the switch can sink. Inside the sensor is a 10K resistor between the supply and output. AT 24v supply it means that it will source 2.4mA at that voltage. For all practical purposes you can regard the output of these sensors as though it is the NO contact of a relay, with the common of the relay being connected to GND.

If you see this page IGNORE IT ! it is wrong, misleading,confusing and confused. http://www.marchantdice.com/worldofc...tch_wiring.pdf

It sounds as though you have a faulty sensor if the power supply buzzes, possibly due to miswiring in the past.

This has all been discussed before.

**Robin Hewitt** · 14-10-2016

Originally Posted by cropwell

Inside the sensor is a 10K resistor between the supply and output. AT 24v supply it means that it will source 2.4mA at that voltage.

Sort of, if you short out a 24 Volt PSU with a 10k resistor it will flow 2.4mA

If you stick anything between the resistor and ground you are unlikely to get 2.4mA

Ohms' Law gives you the Voltage drop across the resistance.