Need Help!- Optical home switch wiring to G540

[mhackney]

Hello all, I could use a little help in wiring up optical home switches to my X2 mini mill interfaced to a Gecko G540. Here are the details:

Ok, I got my optical home switches (NTE3100). I need to interface these to the G540 and power supply and want to sanity check and ask a question. I am using a Keling KL-350-48 48V/7.3A PSU.

So, the NTE3100 are normally closed from reading the data sheet. That means I can connect the 3 home switches in series, say to pin INPUT 1 on the G540 right?

Now for wiring the NTE3100s. There are 4 terminals on the bottom. On the LED side, there is a + and an E (emitter) and on the phototransistor side there is a D (detector) and a +.

Here is my proposed wiring diagram:



thanks,
Michael

[aystarik]

No, this way you can only burn them...
On the detector side you daisy-chain detectors from input1 (it is 2k resistor pull-up to +12V) to ground. '+' should be closer to 'input1'.
On the emitter side, you must make a current source of 30-60(max) mA. So, you need a resistor in series with each emitter, calculated as R = (Vps - 1.7)/0.03. You might use only one resistor if you power supply is greater than 1.7*3 volts (R = (Vps-1.7*3)/0.03), in this case all emitters are connected in series with this single resistor.
Now bad news... 1.9mA (at 30mA of emitter) of your phototransistor is not enough to pull input of G540 down. 2k * 1.9ma = 3.8V, so input will be at 12v-3.8v=8.2v.
To use these devices you will need amplifier of some sort -- either comparator (with open collector output) or schmitt trigger like 74*14 and open collector/drain transistor after...

[mhackney]

Thank for the reply. After I posted this, I dug through my old electronics books and realized it was not so simple. I know how to calculate the resistance (v=ir) but what is the 1.7 v that you are subtracting from Vps? My power supply is 4V. Also, I think I need a separate (12v?) power supply to run these? Otherwise I would need some big power resistors?

thanks,
Michael

[mhackney]

Ah, I got it 1.7v is the forward voltage. The V needs to be greater than this forward voltage.