- Wed Mar 16, 2016 3:14 pm
#43329
Regular opto-isolators have a NPN transistor on the output side. Since NPN transistors have a voltage drop similar to a diode, your multi-meter's resistance measurement won't be accurate (use the diode setting to check if the transistor is switched on).
Also NPNs work only on one direction, so you have to know the polarity of the pins you want to "short". Usually one pin will be GND and the other one a input pin with pull-up, so you can use an opto-isolator to pull the on input to GND.
If you want something, that behaves more like a relay, you could use a solid-state relay like this one (as an example, there are more to choose from):
http://eu.mouser.com/ProductDetail/Pana ... 4t%2fndbDV
It uses 2 MosFETs on the output, in a configuration that can switch AC signals and therefore will have a constant resistance in its "on" state.
Trent wrote:All of the options I have on the table as of now use more than 20ma. I tested my ILD74 with a 150ohm resistor on 3.3v and it still had over 100 ohms resistance on the collector/emitter. I don't recall current draw but should be 22ma.
Regular opto-isolators have a NPN transistor on the output side. Since NPN transistors have a voltage drop similar to a diode, your multi-meter's resistance measurement won't be accurate (use the diode setting to check if the transistor is switched on).
Also NPNs work only on one direction, so you have to know the polarity of the pins you want to "short". Usually one pin will be GND and the other one a input pin with pull-up, so you can use an opto-isolator to pull the on input to GND.
If you want something, that behaves more like a relay, you could use a solid-state relay like this one (as an example, there are more to choose from):
http://eu.mouser.com/ProductDetail/Pana ... 4t%2fndbDV
It uses 2 MosFETs on the output, in a configuration that can switch AC signals and therefore will have a constant resistance in its "on" state.
