can 2 different voltages use the same switched ground?

[strokedmaro]

Please take a look at the attachment Ive drawn up and tell me if its possible. I could use voltage regulators but this would be easier. I also know there would need to be more inputs to the segment driver....just want to know if this would be safe or even possible. THANKS!!!

 

[strokedmaro]

nobody? Maybe you need more info Normal operation: solenoid has 12vdc on it constantly and is controlled by a switched ground supplied by a computer. I basically want to tap into that circuit using a lesser voltage (compatible with the hardware I currently have) to display a digit based on the combination of several solenoids. I know the 4511 is able to operate up to 18vdc but the logic used to make the correct inputs to the 4511 (again, what I have here and by the way not shown in the drawing) is 5.5vdc max. Any help appreciated!

 

[ecerfoglio]

Please take a look at the attachment Ive drawn up and tell me if its possible. I could use voltage regulators but this would be easier. I also know there would need to be more inputs to the segment driver....just want to know if this would be safe or even possible. THANKS!!!

It is possible, and it can be made safe...

But your circuit is not safe (for the 4511 ) because it has no protection against the inductive spikes that the solenoid generates.

You must add protection to the IC from voltages that go outside of the [ground --- +V] range.

One possibility is to add a series resistor (may be 10Khm: as the 4511's inputs are high impedance) and a couple of diodes (1N4148) to +V and Gnd.

 

[strokedmaro]

Thanks!! I will give it a shot and see what happens!

 

[strokedmaro]

Update

After getting this circuit up and running on the breadboard I feel I really over complicated it for this application. Ive decided to just use a few LED's instead of the digit (although it was fun to get it to working ) Just a few questions. Ive attached a new diagram with the proposed LED setup and was wondering if diode "d1" would work or if its even necessary with an LED. Would I also have to protect it against the inductance of the solenoid turning off? Thanks for any help!!!

 

[blueroomelectronics]

What is D1 supposed to do?

 

[chemelec]

What is D1 supposed to do?

In my opinion, Nothing.

 

[strokedmaro]

Well, my brain wasn't in it for a second there...It was originally there when I was going to use a lower voltage (5vdc) as shown in the first diagram that started the thread. D1 was supposed to prevent the 12vdc from reaching the logic (5vdc) that would drive the 4511. I wasn't thinking when I modified it with the led which now uses 12 volts anyway. Is there any need to protect the LED from the inductance mentioned by ecerfoglio in the post above or will it operate fine as is? THANKS