# Circuit for polarity detection

Discussion in 'The Projects Forum' started by kautilya, Dec 5, 2010.

1. ### kautilya Thread Starter Active Member

Apr 26, 2007
39
0
Hi there

Can anyone suggest to me a simple circuit constructed using digital gates for polarity detection? The circuit should be able to detect positive, negative as well as zero polarity.

I need to check the polarity of a dc motor which is controlled by a bidirectional converter. The bidirectional converter has to be controlled in current mode. If any one has ideas regarding the same, i will be grateful.

Thanks and regards

Apr 5, 2008
15,649
2,348
Hello,

Can you post a schematic of what you have upto now?
That way we can see how to connect the polarity circuit.

Bertus

3. ### kautilya Thread Starter Active Member

Apr 26, 2007
39
0
Hi there

Thanks for offering your help, bertus. i have attached the schematic of the circuit in MS word. hope its fine.

thanks and regards

File size:
38.5 KB
Views:
64
4. ### iONic AAC Fanatic!

Nov 16, 2007
1,420
68
It appears that the output voltage is logic level(5V) thus a series resistor of 100 to 150 ohms for a 3V, 20mA LED would do just fine. Wire as Alberto suggsted for both "A" and "B" detection lines.

5. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
Note: Please post schematics as .PNG files or .PDF

If the signal is 5V, a "bi-color" LED would work great for this. A resistor in series as stated above would be needed, I'd suggest 220 Ohms or so.

Then the outputs, assuming the two inputs can source/sink 15mA, would be:
off = no polarity difference
green=polarity one
red = polarity two
yellow = AC or switching polarity changes

6. ### iONic AAC Fanatic!

Nov 16, 2007
1,420
68
220 Ohms at 3V would limit the current to 10mA, which may be all that is necessary for the indicator LED according to Linear.com's calculator...
LED series/parallel array wizard

The bi-color LED would be nice.

7. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
The Red LED in one I checked only had a 2.3V drop, these were Radio Shack ones, so unsure how close to spec they are.

8. ### kautilya Thread Starter Active Member

Apr 26, 2007
39
0
Hi there,

Thanks for the replies. But I am not implementing it in real time. I am trying to simulate the logic in MATLAB/Simulink. Can you suggest how I can do the same in Simulink using logic gates? or any other digital gates? The truth table is given along with the schematic for reference as to the expected binary output.

I have attached the schematic in pdf.

Thanks and regards

File size:
19.4 KB
Views:
34