Like Eggs? I do. I like them scrambled, poached, fried or hard boiled. In Taiwan hard boiled eggs are almost a staple food supplied in 7-11's, Family Mart, Ok Mart and a variety of other chain convenience stores throughout the country. They are usually called "Tea Eggs" because they are boiled slowly in a Tea Mixture that stains the shell brown and penetrates in inner goodness giving them a coffee colored look and slightly sweet flavor.
So I decided to create a simple breadboard based Kitchen Egg Timer for those who like a perfect hard boiled Egg or if they prefer soft or somewhere in the middle. Most egg timers use a rotational variable resistor, which can be difficult to get the time you want unless you guesstimate it. So I opted for a 'hard wired' version using particular resistors and 555 timer programmable by a Dip Switch that allows you to select a timing period between 1 to 5 minutes.
This Egg timer is in our Breadboard Project Kit No3. called "Practical Devices" if you are unable to source the components, along with 5 other fun projects for everyday use.
Anyhow let's boil a timed egg. Enjoy!
- 1 x 0 ohm resistor 1/4 W (Yes, they do exist!)
- 4 x 1k resistors 1/4W
- 1 x 56k resistor 1/4W
- 1 x 110k resistor 1/4W
- 1 x 220k resistor 1/4W
- 1 x 330k resistor 1/4W
- 1 x 430k resistor 1/4W
- 1 x 470k resistor 1/4W
- 1 x 470uF 16V electrolytic capacitor
- 1 x tactile push button
- 1 Dip Switch 5
- 1 x 555 Timer IC
- 1 x 5mm Red LED
- 1 x 5mm Green LED
- 1 x 10mm Piezo Button Speaker / Buzzer
- 2 x 0.1" jumper wires (No insulation)
- 3 x 0.2" jumper wires (Red)
- 3 x 0.3" jumper wires (Orange)
- 2 x 0.4" jumper wires (Yellow)
- 3 x 0.5" jumper wires (Green)
- 2 x 0.9" jumper wires (White)
- 1 x 2.0" jumper wire (Red - Long)
- 1 x 3.0" jumper wire (Orange - Long)
- 1 x 400 point Breadboard
- 1 x 9 Volt Battery Clip
- 1 x 9 volt battery
Step 1: Insert the 555 Timer
Insert the 555 timer into breadboard slots: F15 – F18 / E15 – E18.
Step 2: Power and Component Wiring
Connect the Bus Lines using 1 x 2.0” red wire from Y31 to W31 and 1 x 3.0” Orange Wire from Z31 to X31. Then add the following component wiring:
(A) 2 x 0.1” non-insulated wires at: i1,2 and G16,17.
(B) 3 x 0.2” red wires at: H1, 3 / B17, 19 / A16,18.
(C) 3 x 0.3 orange wires at: Y16, J15 / Y21, J20 and A15, X16.
(D) 2 x 0.4” yellow wires at: Z25, J22 and C12, 16.
(E) 3 x 0.5” green wires at: H11,16 / B10,15 and C17, 22.
(F) 2 x 0.9” white wires at: i19, 28 and A19,28.
Step 3: Add the Resistors
Insert the resistors into the follow slots.
(A) 1 x 0 ohm resistor to: J2,11.
(B) 1 x 56k ohm resistor to: i4, 5.
(C) 4 x 1k ohm resistors to: G3, 4 / G15, D18 / F19, E19 / F22, E22.
(D) 1 x 110k ohm to: A1,W3. 1 x 220k ohm to: A2, W4. 1 x 330k ohm to: A3, W5. 1 x 430k ohm A4, W4. 1 x 470k ohm to: A5, W7.
Step 4: Dip Switch and Tactile Push Button
Add the Dip Switch to F1-5 / E1-5 and the tactile push button to F10,12 / E10, 12.
Step 5: Insert LED's and Capacitor
Place the 2 LED’s. The RED LED goes into slots: H19,H20. H20 (+) is the longer leg. The GREEN LED goes into slots H22,H23. H22 (+) is the longer leg.
Then insert the 470 uF electrolytic capacitor into J17, Z17. J17 is the longer leg.
Step 6: Piezo Speaker
Add the Piezo button speaker. The positive (+) pin goes into F28 and the negative pin goes into E28.
Step 7: Power It Up!
Finally connect the 9 Volt Battery wires to Bus lines: Z3 (-) and Y3 (+). The Piezo speaker will sound out a high signal. To activate the timer select the DIP SWITCH number for the corresponding minute. 1 = 1 min Etc. Then press the button. The Red LED will turn off and the GREEN LED will come on as the countdown begins.
Once the timing ends the Red LED will come on again along with the Piezo Alarm. Please note that the accuracy of the timer in milliseconds can be over or under depending upon the quality of each resistor in the circuit. Generally the timer operates in standard seconds. For the purposes of timing a soft boiled or hard boiled egg, it is fine.
You can experiment with the times by swapping out the various resistors with higher or lower resistance.
Step 8: Circuit Diagram
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