HACK A WEEK

Ahh yet another transistor project!! Well, this will be the last one for a while I promise. 🙂

This is an amplifier of sorts. In fact a viewer of the video posted below with the screen name MonkeyFCoconut summed it up very nicely with the following comment:
“Pretty cool? man. I whipped up your circuit in LTSpiceIV and it seems to have a gain of 95 Million with still enough current to light the LED. This is basically a SUPER-Darlington Transistor 😉 The front end copper strip forms one side of a capacitor, and then when you bring it near a voltage potential a super tiny current flows between air dielectric of the “cap”. This is mega amplified with the high gain BC547’s and viola, the LED lights up. Might be able to detect pre-lightning strikes??”

This is a fun project to build and test out on different objects. It’s surprising what the thing will, “detect”

Keep on hackin!

Parts List:

1 – 1 Megohm resistor
1 – 100K ohm resistor resistor
1 – 22 ohm resistor
3 – BC547 NPN transistors

Schematic:

I’ve been on a transistor theme here lately and there’s one more I’d like to cover, the JFET. JFET stands for Junction Field Effect Transistor. These transistors are well suited for high impedance inputs and since a Piezo electric device measures in the multi-megohm range it’s a perfect match.

I found the schematic for this circuit on this webpage: Design Guidelines for JFET Audio Preamplifier Circuits By Mike Martell Thanks Mike! Great write up.

After some bread boarding and testing I decided this would be a great preamp for a Piezo pickup mounted inside my acoustic guitar. I salvaged a Piezo element from a Roomba vacuum I had in the scrap pile. They use them as a dirt sensor mounted above the rotating brushes as you’ll see in the video.

I glued the Piezo element inside the guitar on the sound board near the sound hole and connected it to a 1/4″ audio jack that I mounted on the lower body side. It sounds great but there is a bit of 60 cycle hum getting in the signal. I’m assuming that this is coming from the circuit being on a bread board. I plan on mounting the components to a PCB and finding a suitable metal enclosure to put it all inside of. I think the metal will help shield outside noise.

This is a pretty easy project to put together. You can get JFETs from most electronics suppliers. I got mine from Tayda Electronics for $.25 each.

Keep on hackin!

Parts List:

1 – 10 ohm resistor
1 – 470 ohm resistor
1 – 1.2K ohm resistor
1 – 1 Meg ohm resistor
1 – .1 uF polarized capacitor
1 – 2 – 4.7 uF polarized capacitors
1 – 100 uF polarized capacitor
1 – J201 Transistor

Schematic:

This is basically a high gain amplifier with feedback that causes the LED to light and flash at a rate determined by the 10u and 330k resistor.
Remove one of the transistors and insert the unknown transistor. When the transistors are inserted with the pins in the correct position as shown in the photo, the LED will flash. To turn the unit off, remove one of the transistors.

Parts list:

1 – 10 uF polarized capacitor
1 – 1K ohm resistor
1 – 330K ohm resistor
1 – 22 ohm resistor

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
Keys
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!

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 talkingelectronics.com website:

LATCHING A PUSH BUTTON – also called: PUSH-ON PUSH-OFF
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: