Gadget Freak Case 110: A Fridge That's Alert for Midnight Snacks
By Design News Staff -- Design News, October 21, 2007
When you've popped in your fridge alarm, getting peckish in the middle of the night and forgetting to close the door — along with escalating electricity bills — will be a thing of the past. Italian inventor Flavio Dellepiane has designed a 3V battery-powered fridge alarm that beeps if you leave the door open for more than 20 seconds. When the fridge lamp illuminates, the alarm's photo resistor lowers its resistance, the IC starts counting down and, after a preset delay, the piezoelectric buzzer beeps for 20 seconds.
Build Instructions | View Parts List | Post a Comment
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| Amt | Part Description | |
| 2 | PCB Mount holders for 1xN cell | 839-3078 |
| 1 | 10k 0.33W Carbon Film Resistor | 296-6300 |
| 1 | Photo Resistor (ldr) | 699-0002 |
| 1 | 100k 0.33W Carbon Film Resistor | 296-4743 |
| 1 | 10 nF 100V Polyester Capacitor | 995-0018 |
| 1 | 100 uF 10V Electrolytic Capacitor | 859-0122 |
| 1 | 1N4148 75V 150 mA Diodes | 935-0242 |
| 1 | 74HC4060 14-bit Binary Counter & Oscillator IC | 236-1836 |
| 1 | BC337 45V 800 mA NPN Transistor | 431-0466 |
| 1 | Piezoelectric buzzer, 13.7 mm | 623-1957 |
| 1 | 1.5V N Alkaline battery | 884-5175 |
| 1 | Black ABS potting box with lid, 64 x 43 x 25 mm | 806-6955 |
| Get Build Instructions | ||
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So, what''''s new here? When I was 12 years old, some 65 years ago, I did essentially the same thing using a Model T Ford ignition coil. These things used a mechanical breaker system employing contacts (points)in series with the ignition coil and car battery. The magnetic field of the spark coil would cause the points to open and then reclose when the current went to zero. The process repeated at a few hundred Hertz to alternately break and make the coil current. The high voltage generated was due to the rapid collapse of the coils magnetic field and electrical resonance between the coil''''s inductance and the commutating capacitor across the points when the current collapsed. The secondary of the coil had about 100 turns of wire for every primary turn to produce a very high voltage continuous spark. Of course it generated much EMI so my folks said don''''t run it while were listening to the radio. The spark avalanch produced in the low pressure gas of a bare tungsten light bulb, though not very high tech, was spectacular!
- 2007-19-11 08:28:22 EST -
The opening paragraph has a typo. It should read: "plasma globe", NOT: plaza globe.
- 2007-5-11 04:34:04 EST -
Could a more powerful device of this design possibly be used to detonate road side Improvised Explosive Devices(IED)prior to a military vehicle reaching the point of explosion? A long boom or a drone helicopter type aircraft traveling ahead of each convoy could trigger the IED?
- 2007-5-11 04:08:03 EST -
Has anyone but me noticed that there is no indication in the gadget freak "case #110 Fridge Alert" as to which is what? While there is a resistor r2, what is it''s value? Besides the photoresistor, there are 2 other resistors, but there seems to be no designation as to what value they are. Ditto the 2 capacitors
- 2007-26-10 02:08:24 EDT -
Well, for those of you who ever wondered if the fridge light goes out when the door closes (we all know it does) however, a while ago the light switch on my fridge door got stuck in the "on" position and the fridge would not cool with the heat generated from the 40W bulb. I went nuts trying to figure out the problem and never even give the light switch a thought. All the other "external" triggering methods you have mentioned would not alert you to this problem. If I would have had the "Light Switch" alarm I may have heard the signal and would have saved a $70.00 service call! Just something to consider.
- 2007-23-10 05:31:17 EDT
