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Problems with Sensor

Posted by Naesstrom 
Problems with Sensor
October 07, 2015 07:32AM
Hi everyone

I'm having some problems getting my capacitive sensor working with my Melzi 2.0 and I was hoping to get some feedback from you.

I bought a LJC18A3-B-Z/BY PNP NO Capacitive sensor from Ebay and since it's a PNP it switches over the negative side:

So I found a nice guide over at reddit that explained that I should connect it as follows:
brown: +12v
blue: z-stop pin closer to bed temp
black: z-stop pin closer to y-stop

Looking at the schematic of the Melzi it looks correct since the pin closest to bed temp is grounded and the other one is the signal one.

The problem is that when I position it in the right place and the sensor closes my chip (the big one) on the melzi gets super hot... I've just changed cards since my old Melzi died on me and I'm afraid this is the reason! When the sensor isn't closed (ie. far away from the glass) the chip is cold as it should be!

So... anyone have some ideas?
Re: Problems with Sensor
October 07, 2015 05:06PM
Please read

"If it was a PNP sensor, the sensor would be sending whatever voltage it was operating at TO the microcontroller, so you'd have the possibility of sending more than 5V to the microcontroller, likely frying the pin if not more in the process. With a PNP sensor, you must use a voltage divider to lower the voltage if the sensor operates at greater than 12V"

so you need that voltage divider cct

And yes, you put 12v onto a 5v pin, this would kill that pin if not the entire processor.


Edited 1 time(s). Last edit at 10/07/2015 05:08PM by Dust.
Re: Problems with Sensor
October 08, 2015 04:17PM
Oh really... I must have missunderstond the difference between NPN and PNP! I have a NPN sensor to but I never tried to use it since I thought that I had ordered the wrong type grinning smiley
I'll try and connect that one tomorrow then!
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