Solenoid circuit sanity-check

[sgpope]

I've created a working prototype of a circuit to open and close a solenoid based on microcontroller output, and now I'm trying to scale it up to run 6 solenoids instead of 1 (only 1 solenoid will be running at a time). The original circuit and my new one are attached. Can somebody take a look at the scaled-up version and make sure it won't burn down my house? Only 3 solenoids are pictured, but you can guess how I'm going to expand it from there. Also, if there's a more efficient way to build the schematic, I'd love to hear it.

Thanks!
Steve

 

[ericgibbs]

hi,
Whats the current rating of the solenoid coils.???

Look at the ULN2803 IC.

 

[sgpope]

They're 12v 450mA solenoids.

Edit: Just checked out the darlington array you suggested. That looks pretty awesome (and would simplify my design a lot). I'll update my schematic and post again (for paranoia).

Another (slightly related) question. What's the simplest way to make this into a permanent device? Right now I'm working on a breadboard, but I think I'd rather build it properly than mount it to my machine on a breadboard.

 

[ericgibbs]

They're 12v 450mA solenoids.

Edit: Just checked out the darlington array you suggested. That looks pretty awesome (and would simplify my design a lot). I'll update my schematic and post again (for paranoia).

Another (slightly related) question. What's the simplest way to make this into a permanent device? Right now I'm working on a breadboard, but I think I'd rather build it properly than mount it to my machine on a breadboard.

hi,
The 450mA for 6 solenoids will exceed the power rating of the ULN.!!

 

[crutschow]

hi,
The 450mA for 6 solenoids will exceed the power rating of the ULN.!!

Eric, you missed his statement that only one solenoid is on at a time.

 

[ericgibbs]

Eric, you missed his statement that only one solenoid is on at a time.

I thought I better mention it, in case he later on decided to switch on more solenoids, but if limits it to just a couple at any time, it should just be OK.

 

[sgpope]

Thanks for the heads-up!

I'm not sure how to wire the ULN. What parts of my circuit does it replace? I don't understand where in the schematic it would go.

 

[ericgibbs]

Thanks for the heads-up!

I'm not sure how to wire the ULN. What parts of my circuit does it replace? I don't understand where in the schematic it would go.

hi,
Look at this image

 

[sgpope]

The ULN replaces EVERYTHING?? If I'm reading that right, I'm just going to wire the output from the arduino to 1, gnd to 9, and the solenoid and 12v to 18 and 10? The ULN has the resistors and all embedded in it?

 

[ericgibbs]

The ULN replaces EVERYTHING?? If I'm reading that right, I'm just going to wire the output from the arduino to 1, gnd to 9, and the solenoid and 12v to 18 and 10? The ULN has the resistors and all embedded in it?

The resistors are internal to the ULN.

Pins 18,17,16,15,14,13, goto the bottom of the solenoid coils, and +12V to the top of the solenoids.
pins 1,2,3,4,5,6 goto the MCU
pin 10 goes to +12V supply
pin 9 to 0V of the 12V supply and the 0V of the MCU.

 

[sgpope]

That's AWESOME. Thanks!!