Napkin Launcher project, need help with electronics please.

Thread Starter


Joined Jun 16, 2019
Hi all,
I’m a first year engineering student and I’m just trying to wet my feet in electronics builds. I am trying to build a pneumatic napkin launcher for a bit of fun with some of my friends and I just have a few questions so that I can build it.

  1. The only solenoid valves I can find are 12v so how can I supply it with enough voltage from (preferably) a 9V smoke alarm battery?
  2. The Micro controller is to make sure that the solenoid only opens for a fixed amount of time, and the input dial is to experiment and set that variable. What components would you recommend purchasing for this?
  3. Given the low energies involved, are these components even required. (is there anyway of running everything through the micro controller to bypass the relay)
  4. If there’s anything else I need to consider please let me know.


Joined Jun 19, 2012
The biggest problem is the battery- you will not get enough out of a standard 9V battery to fire that solenoid.

The battery voltage is starting out too low for reliable operation, then when you add the internal resistance of the battery, the situation becomes hopeless.

Depending on how frequently and for how long the solenoid needs to be fired, you might be able to use a voltage boosting circuit that accumulates a charge in a capacitor (higher voltage) to periodically dump into the coil and make it momentarily pulse.


Joined Apr 11, 2010
  • The relay likely requires more current than the microcontroller can supply. You’ll likely need a transistor (BJT) or MOSFET to control the relay.
  • Since you’ll need something to drive the relay, you may as well control the solenoid directly.
  • Both the relay and solenoid coil will generate a large back EMF spike when they shut off. That will destroy the microprocessor. At a minimum, you need a diode wired in reverse across any coil to prevent this from occurring.
  • The solenoid is not only dependent on the voltage. You’ll need to know the current it will take to operate. Others have noted that a 9V battery will not have enough power to operate the solenoid.
  • There are circuits or modules to boost the voltage of a 9 volt battery. But, Ohms Law and the law of conservation of power, shows that if you increase the voltage, the current decreases. (Power in = power out. Eg., 5V @ 1 A in = 10V @ 0.5A out)


Joined Sep 7, 2010
Not clear how much air flow you need to launch a napkin , if a lot a valve like this (12V) ....

A smaller and much cheaper one ....

you need an air pressure tank ... a plastic drinking water bottle .... and a way to get the air pressurized in the bottle.

this pump will only get a few PSI , to double PSI get two and feed outlet of one into inlet of the other...

No need for any electronics , you throw a switch which opens the valve , and release when napkin flies ...

You have to get a small rechargeable lithium battery 11.2 V ... everything's on eBay