Hello...

I've uploaded a sketch of what I would like to successfully connect: 1) an Arduino controller, 2) a LM7805 regulator circuit, and 3) a MOSFET circuit to switch a 12 soleniod.

When the 24V input is received, the LM7805 outputs a 5v signal to the Arduino. The Arduino responds by sending an output signal which is fed into the MOSFET, which turns on the MOSFET, ultimately switching the 12V solenoid. If I connect the Arduino ground to the 12V supply ground and test just the MOSFET circuit, the solenoid switches as expected. However, if I intend to use the 5V LM7805 signal, I can no longer connect the Arduino to the 12V ground, correct? I must connect the Arduino ground to the 24V ground if I want the 5V signal, correct?

Is there a way to use the two power supplies together with the Arduino? I tried to omit the 12V supply by utilizing only the 24v supply. I tried this by using a LM317 circuit to get from 24v down to 12V. However, when I connected what I had measured (no load) to be 12V up to the MOSFET circuit, the voltage dropped from 12V down to 4V and would no longer fire the solenoid.

Any suggestions? I'm stuck using the 24v supply.

 

all the grounds should be tied together..
and what do you even need the 5V supply for.. Arduino has a little one already built it..

 

Could then use a buck regulator for 24V to 12V for solenoid, but will need a logic level FET or a secondary FET driver.

 

It "could" all just be done with the 12V supply.. Arduino can accept 12V.. solenoid needs 12V.. arduinos regulator will give 5V if needed..

 

so I can safely tie together the ground of the 24v supply and the 12v supply?

I don't think Arduino can read a 24V signal, which is why I need to bring it down to 5V.

Thanks for the help.

 

It "could" all just be done with the 12V supply.. Arduino can accept 12V.. solenoid needs 12V.. arduinos regulator will give 5V if needed..

The 24V is my input signal. It is the trigger for everything else. Arduino is responding to that signal.

 

so I can safely tie together the ground of the 24v supply and the 12v supply?

I don't think Arduino can read a 24V signal, which is why I need to bring it down to 5V.

Thanks for the help.

?? what do you mean "read".. what are you trying to do with that 24V supply..
you can typically use a voltage divider to measure higher voltages..

 

?? what do you mean "read".. what are you trying to do with that 24V supply..
you can typically use a voltage divider to measure higher voltages..

I'm not trying to do anything with the 24V supply. The 24V feeds a heater. When that heater turns on, I want my Arduino to perform a function. the Arduino needs an incoming signal as a trigger to perform the function. I'm not sure, but I don't think I can use a 24v input signal on Arduino, which is why I'm bringing it down to 5v.

 

yeah you don't need a regulator for that..
a simple voltage divider, or an optocoupler for isolation,or a relay, or etc... could be used.

A relay or optocoupler would allow you isolation if you didn't want the 24V ground connected to the rest of the circuit.. It would be 100% electrically isolated then.
stuff here
http://www.w9xt.com/page_microdesign_pt11_opto_inputs.html
and here
http://cq.cx/interface.pl

 

Thanks for the help.