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7805 for 12v to 5v (probe)

Posted by niekz 
7805 for 12v to 5v (probe)
March 07, 2020 11:22AM
First, let me just say I have no formal training with electronics and learn basically everything I know about it online, so please forgive my ignorance in advance.


Trying to add an inductive sensor to a small printer. Printer's mainboard, as I understand, accepts input voltages of 5v for endstop values (ramps based).
I have a 12v inductive probe, powered directly from a 12v external power supply (same as for heated bed). Since I had a couple of 7805's lying around,
and have used them in other projects to drop voltage to 5v, I assumed they would be fine to use in this instance.

The inductive sensor is a NPN sensor which is normally open.

Connecting directly to sensor's output gives me 12v via multimeter.

If I put the 7805 chip between the output signal of the probe and the multimeter, the output reading is 1.3v

I tested connecting the 7805 without the probe (directly from the 12v source) and it regulates to 5v.

Am I missing something here?
Re: 7805 for 12v to 5v (probe)
March 07, 2020 02:28PM
While what you are trying to do seems logical an I see no immediate problems.

It just seem you went in a little unorthodox way of accomplishing the task, as most only use a 30k ohm resister and a 5.1 volt zener diode.



I have been using both the SN04 and TL-W3MC2 proximity sensors while connected to only a 5 volt source for going on 3 years with no problems.

The specs for the SN04-N are
Supply Voltage Min 6 V DC
Supply Voltage Max 36 V DC

The Specs for the TL-W3MC2 are
Supply Voltage Min 10 V DC
Supply Voltage Max 30 V DC


Electronics Technician / Computer Programmer
Re: 7805 for 12v to 5v (probe)
March 09, 2020 03:36AM
Thank you for the suggestion of running it at 5V.

Tested the probe quickly yesterday with 5V and it detects the bed perfectly fine, so ended up just installing it and running off of 5V instead of 12V
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