Monday, April 10, 2017

Homemade Power Supply Update

I decided to add a power switch to my homemade power supply when I  found a really interesting light switch at the Habitat for Humanity store in Round Rock. The switch has two buttons, on and off, unlike the single lever of most light switches.

 I also upgraded the FULL BRIDGE RECTIFIER from 800V 8A TO 50V 25A, added more voltage rails, and more smoothing capacitors on the unregulated rail.


Wednesday, January 18, 2017

Shaky Stick with Pig Tail (Unbalanced Motor with MOSFET)

This project is basically a stick that shakes with a fake pig tail. I recently took apart my old talking stuffed animal toy called Piggy Says. It was an interactive game based on Simon Says. I wanted to reuse parts of it, such as the switch in its tail and the vibration motor that made it seem like it was laughing. The 3 AA battery compartment was from another toy I took apart, because the one from Piggy Says was corroded. The switch was designed to signal an integrated circuit which means it can't handle much current. That's why I added a MOSFET which can handle a higher current. I put a capacitor across the motor to protect the MOSFET from inductive spikes. I added a pull down resistor on the MOSFET to prevent it from turning half on which would cause it to get hot. 

The motor with unbalanced weight.


MOSFET with heat sink (which wasn't really necessary)

Friday, December 23, 2016

Christmas Ornaments 2016

Griffin made these wooden Christmas ornaments from scrap wood he got from Lowes and Home Depot. He used a pattern for a simple tree, and then cut it out with his scroll saw. He drilled a small hole with the drill press so he could hang them. He added patterns with woodburning. Then he put a small nail through the hole and dipped them in clear coat and then let them dry, except for the green one which Mom brushed with clear coat tinted green with oil paint.

Thursday, December 22, 2016

Power Tool Battery Charging Station

I built this power tool battery charging station so I could keep my Craftsman 12 volt drill battery and Worx 20 volt weedeater and switchdriver batteries charged. Mom likes this because it keeps these chargers out of the kitchen. The charging station consists of a short extension cord mounted to the underside of the workbench, a power strip, and a shelf for the Worx 20 volt battery. I used 2 pieces of scrap wood from pallet dividers, screwed to the underside of the main supports of the workbench. The shelf keep the battery off the workbench. The craftsman charger doesn't need a shelf because the charger is mounted to a post.
The Worx battery is 27 watt hours and charges at 14 watts. The Craftsman battery is a much smaller capacity but charges at 45 watts. Since the Worx battery is larger, I think it would work better if it charged with a higher power. It takes four times longer to charge. The only good thing about charging at the lower power is that it might make the battery last longer. Judging by the shape of the Craftsman battery, it appears to contain 3 lithium cells in series. The Worx battery appears to contain ten cells, with five sets in series of two parallel cells.
I like lithium ion cordless drills for driving screws because they are lightweight and have a higher pwm frequency compared to corded ones. NiCad drills have heavy batteries but they seem extremely wimpy.

Monday, December 19, 2016

Homemade Bench Power Supply

This is a benchtop power supply I made from a landscape lighting transformer. It has a bridge rectifier, a large heat sink, and 2 linear voltage regulators. One is for the 9-volt output and one is for the 5-volt output. It has 2 incandescent light bulbs wired in series to reduce current draw. It has a max total DC output of 3.5 Amps. It has max output of 1 amp per regulated rail. All the power consumed by the voltage regulators goes through the heat sink so that I only have to run 2 wires to each. 

This is useful for testing circuits, such as 5-5-5 timer circuits. The 5-volt rail is good for testing circuits that normally use a 9-volt battery so that the components aren't damaged by excessive current. I can charge 9-volt batteries through the 9-volt rail. I use another incandescent light bulb when charging the 9 volt battery to limit the current and indicate when the battery is full. 

9 volt regulator

5 volt regulator
bridge rectifier

Doorknob-based Switch

This circuit that turns a motor on and off is based on an old doorknob from our house. If the doorknob is not turned, the motor doesn't run. Turning the doorknob in one direction or the other completes the circuit and determines which direction the motor spins. This type of switch is a momentary single-pole double throw switch with center off.

Sunday, October 23, 2016

Homemade single battery flashlight

I built this flashlight based on a solar garden light for the boost circuitry and LED. The switch is an American light switch. It uses a single AA battery. The battery door is a 2 1/2 inch hinge. The battery spring is loose in the battery compartment, not attached to the hinge. The positive end of the battery is pressed up against a piece of 14 gauge wire that connects to the switch. I started with a block of wood that's 10 3/4 inches x 2 3/4 x 1 1/2. It's heavy and not very bright, but I plan to use it as a night light. In order to replace the battery, you have to first remove the screw, then open the battery door without losing the spring. Then use the screwdriver to push the old battery out from the other end and then push in a new battery, positive end first. Then put the spring back in, close the battery door, and screw it back on. 

Wednesday, June 29, 2016

Marble Maze-part 4- Vertical Wall

Here is a view of the next part of my marble maze. Marbles travel through the maze on the table top, and then go over the edge to a vertical marble maze wall.
The yellow funnels and some of the other parts are from a previous version of the marble maze that I had at the 2013 Austin Mini Maker Faire. The previous version had two of these vertical walls made of thin plywood, back to back like an easel, set on top of a table. The orange striped tubing is part of a toy from the dollar store that whistles when you swing it around. The blue tube is from a water squirter toy. The grey tubing was originally part of Grandpa's CPAP machine. The yellow brackets are part of my erector set toy. The light blue tubing and the clear channels are from an actual marble maze toy.
Marbles can go down through two different paths, and then join back up at the clear channel right before the chime. When any marble hits the chime, the LEDs on the left light up. Then the marbles continue down through the lower yellow funnel, and hit the bell.

Monday, June 27, 2016

Marble Maze- part 3- Ball Bearing Detector

My marble maze has two parts that detect when marbles go by. One detector works when any type of marble hits it. The other detector only works with metal marbles (ball bearings). It works because the ball bearings are made of steel which is conductive. It consists of 2 pieces of foil tape in series with an LED string. The balls themselves complete the circuit. It was the first system on my marble maze to be powered off 2 D batteries. The ball bearing detector only works on one of the four paths through the marble maze.

Frog visits the sump pump

Today, I looked inside the air conditioner condensate tub and saw a small frog hiding in one of the holes in the brick that supports the float switch. I decided to rescue it because the holes get filled with water and then the pump runs. I moved the frog to my pond in a glass jar. Then it can decide to be in or out of the water more easily, and if it lays eggs, they won't get disturbed by the pump.