Hurricane Evacuation Kit

Hurricane Irene is heading up the coast towards North Carolina and may be making land fall fairly close to where I live, so I thought it would be a good idea to get an evacuation kit together. I also realized that this would be a good video for this week’s “hack” and so I’ve put together a how to of what you’ll need if you need to evacuate your home in the event of an impending natural disaster.

Here’s a list of some things you should think of putting together:

Water – at least 1 gallon daily per person for 3 to 7 days
Food – at least enough for 3 to 7 days
— non-perishable packaged or canned food / juices
— foods for infants or the elderly
— snack foods
— non-electric can opener
— cooking tools / fuel
— paper plates / plastic utensils
Blankets / Pillows, etc.
Clothing – seasonal / rain gear/ sturdy shoes
First Aid Kit / Medicines / Prescription Drugs
Special Items – for babies and the elderly
Toiletries / Hygiene items / Moisture wipes
Flashlight / Batteries
Radio – Battery operated and NOAA weather radio
Telephones – Fully charged cell phone with extra battery and a traditional (not cordless) telephone set
Cash (with some small bills) and Credit Cards – Banks and ATMs may not be available for extended periods
Toys, Books and Games
Important documents – in a waterproof container or watertight resealable plastic bag
— insurance, medical records, bank account numbers, Social Security card, etc.
Tools – keep a set with you during the storm
Vehicle fuel tanks filled
Pet care items
— proper identification / immunization records / medications
— ample supply of food and water
— a carrier or cage
— muzzle and leash

Here’s hoping all of us here in NC get through the weekend with minimal damage…

Keep on hackin!

The push on push off transistor switch

You’re probably familiar with single button on/off switches. Most of the ones you see now on devices are IC logic switches but there was a time when these types of switches used transistors only. I can remember when the first stereos of the 70s had “soft touch” controls. One button turned a device on or off without actually mechanically switching the circuit.
This project demonstrates a simple version of this type of circuit. It uses three transistors, two NPN and one PNP. There’s also a capacitor which gets charged and discharged, and this is what makes the button capable of performing two functions with the same contacts. The output of this circuit is negative.
Here’s a description of the circuit as it appears on the website:

When the circuit is turned on, capacitor C1 charges via the two 470k resistors. When the switch is pressed, the voltage on C1 is passed to Q3 to turn it on. This turns on Q1 and the voltage developed across R7 will keep Q1 turned on when the button is released.
Q2 is also turned on during this time and it discharges the capacitor. When the switch is pressed again, the capacitor is in a discharged state and this zero voltage will be passed to Q3 turn it off. This turns off Q1 and Q2 and the capacitor begins to charge again to repeat the cycle.

This is a useful circuit that can be put to use on many devices. Try building one and see what you can switch on and off with it.

Keep on hackin!

Parts List:
2 – BC547 NPN Transistors
1 – BC557 PNP Transistor
3 – 470K resistors
2 – 10K resistors
1 – 1K resistor
1 – 100K resistor
1 – 1M resistor
1 – 1uF polarized capacitor
1 – Momentary contact switch
1 – 9 volt battery and holder

The Schematic:

Class AB Audio Amplifier

This week we’ll take a look at another type of audio amplifier, the class AB amp. As we saw in Hack #19 the class A amp has a transistor that is biased with a voltage that makes it essentially stay turned on all the time. This single transistor handles the entire waveform both positive and negative.
The class B amplifier uses two transistors. One handles the positive side of the waveform and the other handles the negative side of the waveform. Each transistor is in an off state until the waveform crosses over the zero point and then it must turn on. This takes about 0.7 volts so there is a small amount of time that the transistor is not amplifying the signal. This lag time at the crossover point can cause distortion. There is a way around this however, the class AB amplifier.
In the class AB amp the transistors are biased in such a way so as to never fully turn off. They are kept on by two biasing diodes which allow a small amount of collector current to flow even when there is no signal present. This means then that the transistor will be “ON” for more than half a cycle of the waveform but much less than a full cycle giving a conduction angle of between 180 to 360o or 50 to 100% of the input signal depending upon the amount of additional biasing used. The amount of diode biasing voltage present at the base terminal of the transistor can be increased in multiples by adding additional diodes in series.
There’s a great tutorial on class AB amps on I encourage you to visit this site where you’ll find a wealth of educational information on electronics.

This project is fairly easy to build and all the parts are readily available. You can use just about any NPN and PNP transistors, just make sure they’re within similar specs to each other.

Keep on hackin!

Parts list:

2 – 2N3904 NPN transistors
1 – 2N3906 PNP transistor
1 – 47 uF electrolytic capacitor
1 – 470 uF electrolytic capacitor
1 – 100K ohm resistor
1 – 1K ohm resistor
2 – 1N4148 diodes


The Single NPN Transistor Audio Preamp

Here’s a great little project that goes well with the LM386 audio amp. It’s a good first time transistor project because it’s simple and demonstrates the common emitter class A amplifier circuit with only six components in the signal path.

Here’s an excerpt from a great tutorial I found on NPN transistors:
A “Class A Amplifier” operation is one where the transistors Base terminal is biased in such a way as to forward bias the Base-emitter junction. The result is that the transistor is always operating halfway between its cut-off and saturation regions, thereby allowing the transistor amplifier to accurately reproduce the positive and negative halves of any AC input signal superimposed upon this DC biasing voltage. Without this “Bias Voltage” only one half of the input waveform would be amplified. This common emitter amplifier configuration using an NPN transistor has many applications but is commonly used in audio circuits such as pre-amplifier and power amplifier stages.

I powered this circuit with a single 3V coin battery I salvaged from an old computer motherboard. It works just fine at this low voltage because it’s just a preamp. Go build one and keep on hackin!

Parts List:
1 – 2N3904 NPN transistor
2 – 10K resistors
1 – 100 K resistor
1 – 0.1 uF ceramic capacitor
1 – 1 uF ceramic capacitor
1 – 3V – 9V battery and holder