Cigar Box

Hi, Raul. The easiest way to get a motor to open, then close a lid is to put a cam on the shaft of the motor, then make a lever and roller such that the rising of the cam causes the lid to open, and when the cam turns and its radius becopmes less, to close. That requires a geared DC motor that will take a couple of seconds per revolution. The big advantage of this is that you don't have to worry about reversing the motor. If you've got that kind of a motor, then you might be able to accomplish the following simple circuit, which will let you do what you want.

In addition to your two pushbuttons, you'll need a means to tell if the lid is fully open or fully closed, to stop the motor. This can be done by getting a couple of small press fit magnet switches. These are available as All Electronics P/N MS-11, for $2.25 USD per set. You'll need two sets. These normally closed switches will open when the matching magnet is in proximity. Place two of the switches facing opposite sides of the cam, and put one magnet on the cam itself such that, when the lid is fully open or fully closed, the magnet is in front of the appropriate switch.

What you do next will depend on the motor you've chosen, specifically its voltage and the current draw while it's on. Assuming you've got a

` PB1 ` T ` --- ` .--------o o-------------o----------o----------. ` | | | | ` | PB2 | | | ` | T | | | ` | --- | | | ` o--------o o-------------o | D1| ` | | / \\ - ` | | ( M ) ^ ` | | \\_/ | ` | SW1 SW2 | | | ` o-------o o----o o---' | | ` | \\--- \\--- | o----------' ` | .-. | ` | | | | ` | 47 ohms| | | ` +| '-' | ` --- | |/ ` 3V - o--------| Q1 ` | | |>

` . .-. | ` | 1K ohm | | | ` | | | | ` | '-' | ` | | | ` -------------------------o----------' (created by AACircuit v1.28.5 beta 02/06/05

Other components shown above are Q1, an NPN power transistor (All Electronics P/N TIP29C, $0.60 USD ea.), D1, a 1 amp rectifier diode (A-E P/N 1N4001) and a 47 and 1K ohm resistor (available in packs of

Here's how the above circuit works: At rest, the motor cam magnet is over one of the normally closed switches SW1 or SW2, so no current is flowing there (the switches are in series). Neither pushbutton PB1 or PB2 are being pressed, so no current is going to the base of the NPN transistor Q1 from any source. That keeps Q1 and the motor M off. But when you press either pushbutton, current will flow through that switch and the 47 ohm resistor to inject about 50mA into the base of Q1, which will turn Q1 ON, allowing current to flow through the motor and turn it on. As the cam and the magnet moves off the magnet switch, it will close. That will allow current to continue flowing into the base of the transistor through the two series magnet switches, keeping the motor on. It will stay on until the cam moves the magnet over to the other magnet switch. That will interrupt the base current, turning off Q1 and the motor until another pushbutton is pressed.

The 1K ohm resistor from the base of Q1 to GND helps ensure the transistor Q1 will really be off when there's no current through the 47 ohm resistor. It's optional, but recommended (as it reduces leakage current when the transistor is off, which will make your batteries last longer). The diode D1 is necessary to prevent the inductive kick of the motor from destroying the transistor when it tries to turn off.

The idiosyncracy of this setup is that either switch can make the lid open or close. Unless there's somebody lurking inside the cigar box, there shouldn't be a problem with that switch. So, if you can live with having the outside switch having the capability to open or close the lid, this will solve your problem. Look at it this way -- "It's not a bug -- it's a feature!" ;-)

The above example is for a small 3VDC gearmotor scrounged from a kid's toy. If you've got room in the cigar box, you should use C or D batteries for this. Half an amp is too big a load for two AA batteries, but if the motor is smaller and you're not planning on many cycles, you might be able to get away with AAs. But if your motor has another voltage or a higher current, you might want to post back with your specs. There are some limitations to the above circuit, and you'll probably at lest want to change resistor values. If your motor is more than 4.5V, it might be better to use a MOSFET for a higher current motor.

If you need battery holders or other components, you might want to go to the All Electronics website:

By the way, while you're there, sign up for their free catalog. They have a lot of good stuff for projects like this.

I hope this has been of use. If it doesn't work for you, please post again with more information and your requirements.

Good luck Chris

Thanks, if I get it to work I'll post some pics. Thanks again. Raul