# Science project: Suggestions for timer and pull solenoids

Discussion in 'The Projects Forum' started by EvaM, Dec 11, 2010.

1. ### EvaM Thread Starter New Member

Dec 11, 2010
2
0
Hello,
my daughter (11) is working on a engineering project for her science class, and I need to get advice on where to purchase supplies for the project. I would like to buy them online, because I have not had much luck with local stores. Of course, any other input is also appreciated, because my background in all of this is limited. Below is a description of the project followed by specific questions we have.

The project: She wants to construct a sequential alarm clock, because she wants to solve the problem of getting out the door on time in the mornings. The goal is to have a buzzer go of at a certain time (let's say 6:40am - she get's up), then have another buzzer go off at 7am (she wakes me up ), and at 7:25am (we walk out the door). She figured out that she needed to construct two parallel circuits that are each powered by 9-V batteries. The first circuit will hold the timing mechanisms (see below) and one buzzer (I am calling this the timing circuit). The second circuit has 2 buzzers (buzzer circuit). The reason why she uses two circuits is, because the buzzers we found require a minimum of 3 V.

Set up of the circuits: The timing circuit consists of a timer, a buzzer, and two pull solenoids (in a serial set-up). A timer triggers the first buzzer. At the same time, each of the two pull solenoids open a trap door on a container, which starts to release sand. The sand will flow into a cup that is set on a lever that is counterweighted. Once enough sand is in the cup, the lever goes down and completes the buzzer circuit and the two buzzers go off. They go off sequentially, because the two containers with sand contain different amounts of sand and, as a result, the buzzers are triggered sequentially.

A general comment: The object of this project is for my daughter to learn about circuits, fulcrums etc. The reason why we decided on using this set-up is so her project has also an experimental component to it e.g., she needs to figure out how much sand to use to get the timing of the last two right.

Our questions:
1. Timer: I have no idea what we can use as an initial timer. Any suggestions would be appreciated. Please include where to purchase it too.
2. We need pull solenoids that can run off 3 V. Is it possible to get solenoids for this voltage? Where can I order them?

Again, we also appreciate any other input you may have for us.

2. ### tyblu Member

Nov 29, 2010
199
16
Normally, one would use a Real Time Clock (RTC), but they are a bit tricky if no experience with ICs; you may want to get an alarm clock kit like this one (note: requires soldering).
For parts, it depends on where you are from: where are you located? If North America, DigiKey, and Mouser are large distributors of electrical parts. Sparkfun (linked above), LadyAda, and a handful of others are "hobbyist" distributors. If Europe or Australia, Farnell/Element 14 can be added to the mix and I'm sure there are others, but I'm not local. Looking at DigiKey's website, click the "Products" tab, then scroll way down to "Motors, Solenoids, Driver Boards/Modules" and click "Solenoids". You'll see there are only 12V and 24V options; the same goes for Mouser. So, no, 9V won't cut it (without fancy circuitry), but it doesn't take much to find a 12V wall-wart (AC adapter).

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3. ### Otaku Active Member

Nov 19, 2008
128
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4. ### Kermit2 AAC Fanatic!

Feb 5, 2010
4,165
1,120
www.jameco.com

I've used them and believe them to be reputable. They offer kits of various types; books of all kinds, and "grab bags" of all sorts. Those are my favorite and I order them about once a year. Never know what you'll get.

5. ### Kermit2 AAC Fanatic!

Feb 5, 2010
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1,120
I would also urge you to use a higher voltage power source. The 'wall wart' mentioned would be good. Solenoids use LOTS of current. The other option is to get a single small 12volt lead acid(3-10Ah), and use transitor or mosfet switches to activate the solenoid. The lead acid battery is only connected to the solenoids. This would let the rest of the circuit be operated on small battery pack and AA's in it, would last longer than the battery powering the solenoids.(If they are used often)
OR
Get an abandoned computer power supply and use it. Would be much less portable

(You can add a resistor to the buzzer and use it at the higher voltage.)

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6. ### EvaM Thread Starter New Member

Dec 11, 2010
2
0
Thanks to all of you who responded to my inquiry. I will look into your suggestions and might be back with some more qs.