Thread: Electronics - Mixing 24v and 5v

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I'm toying with my first pneumatic triggered prop and I'm working through some technical details of the trigger and the prop.

My controller is a 5v device; the solenoids are 24v.

I don't want to deal with two wall warts.

Is voltage regulation as simple as it seems? To I just hook up an LM4040 or MC33269 with the 24v and I just get 5v out of the Vout?

Both the LM4040 and MC33269 have similar packaging. Is there a significant difference between the two?

Kurt

Kurt, you might want to pm Otaku, he is REAL GOOD with all the electronic stuff. If he sees this I'm sure he'll reply.

My advice would be to use two wall warts.

The two devices you mentioned will not work. The LM4040 is used for voltage reference only and the input voltage for the MC33269 is 20V.

Typically you would use a LM7805 to regulate 5V. It has a maximum input voltage of 35V. It also has a maximum output current of 1A (if you use a heatsink). I don't know what the current requirements are for your controller are, but I would assume it's less than 1A.

I still would recommend using two wall warts, however. You should keep your "control" and "switching" power seperate. You'll save yourself some headaches if you do.

I second the LM7805.

Going from 24V to 5V is a huge drop, which creates a lot of heat on the LM7805 so you MUST heat sink it. The whole package will be very hot to the touch so mind where you put it.

7805: http://search.digikey.com/scripts/dk...e=LM7805ACT-ND

Look at the typical application picture on page 22 of the data sheet. You want to put a .33µF cap on the input and .1 on the output.

.33 cap: http://search.digikey.com/scripts/dk...l&name=P928-ND
.1 cap: http://search.digikey.com/scripts/Dk...l&name=P984-ND
clip on heatsink: http://search.digikey.com/scripts/Dk...&name=HS121-ND

choose USPS First class mail for your shipping option for the cheapest.

What controller are you using? Is it possible that the controller has its own built in 5 volt regulator? I know the EFX-TEK Prop1 runs at 5 volts, but it has a built in 5 volt regulator and you can power it with the 24 volt supply that you'd be using for the solenoids.

Concur with gmacted. In my experience, in the long run, you have less problems separating your relays/motors from your controller. I had a wiper motor controller wreak havoc with my prop-1 before I separated their power supplies. Good luck!

Thanks for the replies. I hate the idea of two warts on each prop, but it sounds like the time saved avoiding the single power source offsets the monetary cost.

@gmacted: Thanks for the warning on the power max. I got my minor in EE nearly 20 years ago. I haven't looked at more than a couple of datasheets since then. It didn't occur to me to check the max input V.

@The Pod: I have two arduino dec controllers. The include a MC33269 that is used to drop the 9V (battery or walwart).

I agree with gmacted. I've tried using common grounds on different voltage/function devices with mixed results, especially where a DC motor was involved. Using separate warts solved the problems. In your application, you may find that the controller gets a transient from the solenoid coil and re-triggers unexpectedly. BTW, 5VDC cell phone chargers are plentiful at the thrift stores and usually run around 0.8A.

I have a ton of 5v, just no 24v.

Fwiw, the devices being controlled by the prop is a 24v 5 port with closed center SMC solenoid.

What would you recommend for isolating the 5v and 24v circuit? A relay seems like a safe choice, but I'm a little concerned about the potential kickback as the coil is deengerized. Would an opto-isolator be sufficient?

Kurt

I Use both a diode and a opticoupler to protect the controller board when the coil collapses. And I know it was said before but I agree,it is best to use two warts = two transformers. The only time I would use Ic's is to drop the voltage from 9 to 5 volts max (lm7805). Remember that energy has to go somewhare so it is converted to heat.