I'm still working on my automation project for my observatory and it has come time to hook up my roof motor frequency converter. This device will control the 240v 3 phase motor.
It has a terminal strip for digital and analog input/output. The first problem is its 12v .. There are two options, High: +12..+30 and Low: 0..+12. So I have set it to low and I now have a common line (ground) and the control line (12v). When I short the two (bring it low) the motor turns on. When I open the circuit (bring it high) the motor shuts off. I used a simple button on the breadboard to test it. There is also others for changing the direction, enabling the local keypad, and other things. Plus analog lines (0..10v) for reading things line the RPM, Torque, current, etc.
All well and good. Question is, how do I hook it up to my Netduino? They are 0..+3v .. My first thought was an NPN transistor (2A2222). But it was odd. I started with the start/stop line and a simple 9v battery with an on/off switch so I did not fry my Netduino board. I hooked up the motors digital line to the emitter on the NPN and the motors common ground to the NPN base. I then hooked up the 9v+ to the collector. I would have thought that the 9v- would go with the other ground on the NPN base. But it had to be hooked up to the NPN emitter with the motors digital line. When I turned on the 9v battery, the motor started, and when I turned off the 9v, it stopped. Seems to work out.
My question is, is this all correct? Do I dare hook it up to my Netduino? Or have I done this all wrong and there is a better way that I should be doing this? And what happens when I hook the next I/O line up .. my Netduino ground is now "hot" with 12v. I have never hooked up a device that supplied its own power before .. I have only been hooking up IC's and LED's that the Netduino powers.
If anyone with a bit more experience with this stuff can help, it would be greatly appreciated.
Roy
Help with Digital Output
Started by Roy Salisbury, Jun 13 2012 08:31 PM
2 replies to this topic
#2
Thomas Rankin
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Posted 14 June 2012 - 03:06 AM
Roy, have you considered using an optoisolator / optocoupler to physically separate the electrical circuits? Not sure if you want to read the analog, but for basic switching it should make you feel safe that you aren't going to fry your netduino.
#3
Roy Salisbury
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Posted 14 June 2012 - 03:58 PM
Roy, have you considered using an optoisolator / optocoupler to physically separate the electrical circuits? Not sure if you want to read the analog, but for basic switching it should make you feel safe that you aren't going to fry your netduino.
I have not figured out how to deal with the analog lines yet, but for the digital output lines I am going to go with using some 3v relays. I have tested it with some 5v relays and it works just the way I expected it too, but since the N+ is using 3.3v I figured the 3v relays would be better.
But hopefully someone can suggest some options on reading the analong lines.
Roy
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